Hello again:

Sorry to poast twice in one day, but I have set up a survey
on the onelist website (you can access it in the member
center, then click on the Spectroscopy List link).  This
survey is completely voluntary and also completely
anonymous.  I have devised it (it is only one question this
week), to help me to identify the dynamics of the mailing
list community and the interests of the members.  I will
most likely set up a new question every week or two weeks to
address a question that will better help me identify the
specific interests of our community.

Remember, you do not have to answer the survey.  It is
COMPLETELY voluntary.

The question for this week is:

What is (are) your spectroscopic and/or analytical area(s)
of expertise?

There are ten choices, and you may choose as many as apply.
You may reply to this question at the website as I mentioned
above at www.onelist.com.  Simply login, click on member
center, and click on the Spectroscopy list link.  There will
be a link for the current survey.

Thanks again, and I apologize for two posts in a matter of
hours.

Your friendly list moderator,

Jesse Greever

University of Missouri - Columbia

Hello all Spectroscopy Subscribers:

Your friendly list moderator here.  Just wanted to welcome
our newest members and let everyone know that we currently
have 63 members from all over the world.  I have been
extremely pleased with the discussion that has been going
thus far, and I am also ecstatic about the recent influx of
new subscribers over the past few weeks.

One thing that I want to pass on from the administrators at
ONElist, (and normally I won't pass on these kinds of
mesages) is that ONElist has introduces its ONEReach
program, whereas the list that grows by the most amount
between April 19 and June 19, 1999 will be given $5000 to
donate to the charity of the list's choice.  Normally,
things like this don't interest me at all, but we have grown
from 14 members to 66 members since April 19 (which, if they
are counting by percentage, we have almost grown by 500%).
I don't know all of the specifics, but I just wanted to pass
this on for two main reasons:

1.  JUst to brag about our tremendous growth and interest
over the past few weeks, and

2.  To throw this out to see if we are interested in a
"membership drive", as it were.

Please, if you have the time, give me some feedback on this
idea.  If there is an overwhelming positive response, we can
come up with some options to boost the growth of the list
even more.  If there is an overwhelming negative response,
consider the notion null and void (as well as any notions
that may come up like this in the future). I would just like
to get everyone's feelings on this.

I personally think that this would be a great thing to be
able to contribute some free money to charity in the name of
spectroscopists everywhere, but this is a democratic list,
and I will bend to the will of the masses.

Thanks again for the great response and keep the discussions
coming.

Jesse Greever

University of Missouri - Columbia

Hi John,

If you email me a fax number, I can fax you a copy of a paper I wrote on
the design of UV photometers. There are actually two papers of interest
(perhaps), one about resolution effects (where linearity is the big
issue) and the other about geometry effects (the merits of single vs
dual beam, etc) WARNING - They are kind of commercial, as the foregone
conclusion is that the photometers built by the company I worked for
were obviously the best designed. Oh it is embarassing how low we have
to stoop sometimes.

But more seriously, I don't think that you can easily come up with a
relationship to gauge the sensitivity of n to changes in filter
bandwidth or to center of the band. The order of the approximation is
going to be really important. I suppose that the closer n starts out to
1, and the flatter the molar absorption spectrum in the region, the less
sensitive you are to band shifts or filter broadening. I don't know if
this helps or not, but I believe that it can be shown (if I did my
algebra right) that:

Given two absorbing wavelengths traversing the optical path, of
intensity I1 and I2 at wavelengths lmda1 and lmda2.

Given an absorber with molar absorptivity K1 and K2 at lmda1 and lmda2
respectively, and the K2 is K1+DK, then the absorbance is approximately

ABS(C) = (K1 + DK/2)*C +((DK*C)^2)/6 +((DK*C)^3)/24

So what this says is that

IF C is small or DK is small such that DK*C^2 is negligibly small, then
the absorbance is directly proportional to the concentration, with the
constant of proportionality being the average of the two molar
absorptivities

As C gets bigger, or if DK is sufficiently large, you have to include
quadratic and cubic terms (DUH AIN'T this a revelation ! It gets
non-linear)

The only point of this is that I am not sure that a direct C^N term in
the exponential term is what you want to do. Something like k*C + K*C^n
might be better. For small C, with n > 1 the effect of this term is
negligible and you get a linear response. If K is negative, the there
will less net absorbance as C is increased, and you get the sort of
curvature you want to see.

Just a thought or two

Regards,

Phil

John M. Jarvis wrote:
> Hi --
>
> I am developing a filter photometer and have found the equation
>
> I = Io*exp(-k*C^n) to work quite well.
>
> Where:
>
>  I is the transmitted intensity of the incident beam intensity, Io
> k the absortivity at a constant pathlength
> C is the concentration of the sample
> n is a constant (n approx = 1) that depends on the sample, pathlength,
> filter,
> etc.
>
> When n = 1 this equation is just Beer's law.  When filter bandwidths are
> larger than the absorption feature and/or stray light becomes important,  n
> <> 1.
>
> I am using this equation based on memory.  I would like to be able to guage
> the sensitivity of n to filter bandwidth or changes in the filter
> transmission wavelengths with temperature.  Can anyone point me to a text
> book that has a derivation that includes the exponent?
>
> Thanks in advance,
>
> John M. Jarvis

Hi John:
I am not sure but I think that Ingle and Crouch in "spectrochemical
analysis" (prentice hall) talks about deviations from beers law.
sincerely,
Mazdak

Hi --

I am developing a filter photometer and have found the equation

I = Io*exp(-k*C^n) to work quite well.

Where:

  I is the transmitted intensity of the incident beam intensity, Io
k the absortivity at a constant pathlength
C is the concentration of the sample
n is a constant (n approx = 1) that depends on the sample, pathlength,
filter,
etc.

When n = 1 this equation is just Beer's law.  When filter bandwidths are
larger than the absorption feature and/or stray light becomes important,  n
<> 1.

I am using this equation based on memory.  I would like to be able to guage
the sensitivity of n to filter bandwidth or changes in the filter
transmission wavelengths with temperature.  Can anyone point me to a text
book that has a derivation that includes the exponent?

Thanks in advance,

John M. Jarvis

Hello Ulrik,

no, I have never been involved with these
particular measurements. If you want you
can describe to me what exactly you have done
(as far as the NMR side, not the chemistry
involved) and I can then comment and maybe
even be able to come up with a suggestion.
I will be busy at work for the rest of the week
though, so my answer may take a while.

Rudi

Hello everyone:

Your friendly list moderator here.  Just wanted to send a
quick message saying that I have received a great response
lately (in the subscription department).  We are now 51
members strong!  Yeah!

Keep those messages coming.  I will be posting another
announcement to some newsgroups in the next few weeks or so.
I seem to be getting a pretty good response from that venue.
If any of you know people who might be interested in a list
like this, tell them about it.  The more the merrier, I say.

Till next time.

Jesse Greever

Hi to all:
My research area is about preferential solvation.
If anyone of you works on preferential solvation
especially its effects on solvents I'd be glad
if you respond especially if you know of any articles
which theoretically explore the effects of preferential
solvation on spectroscopic probes, or simply offer
a microscopic explanation on preferential solvation.

Thanks,
Mazdak

Hello Rudi,

Thank you for responding my question.  I will explain it a little more
in detail.

As I mentioned in the other mail, my product is a racemate and
achieving resolution is not quite simple.  The IUPAC name of the
molecule is 2-oxatetracyclo[5.4.0.0(1,8).0(5,11)]undec-9-ene.  So it
has only 1 heteroatom, an oxygen, which makes it a very apolar liquid.

In the NMR-experiment, I added several kinds of chiral lanthanide
shift reagents (Europium tris[3-
(heptafluoropropylhydroxymethylene)-(-and+)-camphorate] and the
the same ones with Ytterbium as lanthanide).  The problem with
this molecule is that it doesn't give a clear singlet signal, so other
signals shift into each other and you cannot see anything anymore.
What I don't know for sure is that I did those experiments the right
way.  I didn't have a procedure, so I just added the shift reagents
until 'something changed'.

Have you experience on using chiral shift reagents ?

Best regards,

Ulrik

Hi all,

I am a NMR spectroscopist in physics and
just lurking in here so far.

About Ulriks problem:
Ulrik, that substance that you are studying,
is it a liquid or a solid? When you said that
you tried NMR and got no resolution, what did
you exactly try? NMR has many 'tricks' that
could gain you 'extra' resolution.

You may need another working field or, if its
a solid you are studying, you may need to apply
MAS or multi.dim. NMR to improve resolution.

Rudi

Hello everyone...

Your friendly moderator here.

It has been brought to my attention that there
have been some problems with some of the messages
in the archives, and messages received by some
of the members of this list.  The problem stems
from the fact that ONElist is unable to autowrap
long lines in an email message.  I have a few
quick fixes for the list as of now.

1.  If you post messages directly from the ONElist
site, it may be necessary to use a hard return
at the end of each line.  In other words, before
the last word in the line reaches the margin, and
wraps to the next line, you may have to press
return.  This should ensure that we will not have
any long lines.

2.  If you post from a UNIX system, for example,
using PINE or ELM, I think that these emails
should use an autowrap, or will automatically use
a hard return-like mechanism.  If you have the
option of posting, using a UNIX mail system,
please use this.

3.  For mail systems like Outlook Express or
Hotmail, I don't know right now, except maybe
trying to find an autowrap option for long lines.

If anybody knows of any way to remedy this
situation, please let me know.  I am trying to
find out from ONElist if there is anyway to fix
this.

On the bright side, our membership has topped 40
members.  This is far beyond my initial expect-
ations.  Let's keep up the good work.

Till next time,

Jesse

Hi,

I'm currently working on an enantioselective separation by GC (HP 5890 sII),
but it isn't working very well so I think I'll have to give up this and focus
on an other technique.  I've already tried NMR with chiral lanthanide shift
reagents but this didn't give any resolution either.  So right now I am looking
for an new, very sensitive technique.

Does anyone know the profits of HPLC  to GC for enantiomer separations ? Are
there any other techniques that I can use (the only thing I know about my
product is its formula, but I don't have any info about specific rotation data
etc)?

Thank you for any suggestions

Ulrik

Hello all:

Your friendly list moderator here (on his birthday...just a stupid little plug
for me).

I want to announce that I posted a new announcement about the list on a number
of scientifically focused internet newsgroups yesterday...and I am pleased to
report that our numbers have nearly DOUBLED!  Yesterday we were 18 in number,
and currently we have 33 members.  We have an incredible cross section of the
world on this list already.  We have members who reside in Azerbaijan, Taiwan,
the US, Great Britain, Belgium, Sweden, and the Netherlands (just to name a
few).  It also appears that we have people in the commercial sector as well as
purely academic and application areas.  Let's keep up the good work.

I would like to give special welcome to our new members, and restate my one
rule:

There are to be no junk posts.  This includes, but is not exclusive to,
advertisements, "get-rich-quick schemes", and announcements about pornography
sites.  I reserve the right to ban anyone from this list who posts messages of
these types.  If any post is marginal in its content, I will warn the sender
ONCE, and delete the message immediately, so that no one on this list will be
bothered by it.  I want this list to be productive, and I WILL NOT tolerate
offensive language.  Thank you all for abiding by these rules thus far, and I
know that I do not anticipate having any problems with this in the future.

Thanks to all who have subscribed...let's keep the fruitful discussions coming!

Till next time,

Jesse Greever

University of Missouri - Columbia

Rob:

You are right to be suspicious of turnkey instruments...the one I work with was
also supposed to be turnkey (everything was completely manufactured), but I have
it opened up every day optimizing it.  The problem with turnkey lasers, is that
the parts you need to get to for tweaking, are generally difficult to access.

Also, in answer to your question...why build an Nd:YAG (or YLF, or YVO)?  Well,
our Ti:Sapphire system is made to be ultrafast, low rep-rate, which is great for
my experiments, but we have another area of our lab where we measure
fluorescence lifetimes and do time correlated photon counting experiments.  It
is this area that needs a new picosecond, high rep-rate (40 MHz) laser. 
Recently, our old Nd:YAG laser died on us (it was about 8 years old, probably
100 years old in YAG years), so with the arrival of new grant money we will be
building a diode pumped YAG system (our old one was arc lamp pumped -- pretty
low conversion of power from lamp to laser output).

Well, I am happy to report that we have six new members that subscribed
overnight (at least overnight for me), bringing our total to 25
subscribers...we're doing great...keep the discussion coming!

Till next time,

Jesse Greever

University of Missouri - Columbia

Hi again,

Jesse.. I may have been a little luckier then you were, because where buying a
turn key system, however I will be doing regular tweaking of the amplifier
section of the system and will be using an UV generating OPO, that will be
supplied with output of the amplifier. to generate approx 4 ps long UV pulses.
As I said it's virtually turn-key, but I'm usually a bit suspicious about that
kind of statements. At least thanks for your kind advice, some of it sounds
faintly familiar.

The Photon Echo experiments sound exciting and I would in general be
interested in your experiences in building a YLF-laser, although I'm wondering
why you actually would want to build one.

Well Monday next week our Ti:Sa is going to be delivered, so wish me luck
installing it,

Greetz

Rob

Hello to all spectroscopy members:

Your friendly moderator here again.

Rob...I don't think I responded to your message
about you doing work with Ti:Sa lasers.  I am
not exactly sure what would be a good reference
but let me give you a few tips that were given
to me by the manufacturer of the Ti:Sapphire laser
that we use in our lab.

1.  Ti:Sapphire rods are fairly robust, but can be tempermental.  It is always
wise to make sure that your rod faces are impeccably clean, but definitely see
the manual for proper cleaning instructions.

2.  If you are using a manufactured OPO (or OPA), be aware that they do require
some regular alignment.  It is wise to make sure that some apertures are in
place to aid in the alignment procedure.  I assume that you will be generating
continuum light with a Sapphire window, and it is important that the white light
that is generated is single filament mode (a striated pattern is not good).  The
white light also has a tendency to flicker, which may mean that you may have to
rotate the window slightly to optimize the output.

3.  I assume that you will also be using a "photon splitting" NLO crystal for
visible tunability.  Simply put, the angle of incidence of the white light
determines the color of the output.  Be aware that simply adjusting the timing
of the amplifying pulses will not completely optimize the output.  Some spatial
adjustment of the UV pump pulse may be necessary to get the desired amount of
pulse energy out.

4.  Also, be very careful about the pulse energy coming in the Ti:Sa REGEN
cavity (if that is relevant).  Pulses that are in the femtosecond regime can
damage optics pretty badly.  Therefore, it is wise to possibly stretch the
pulses out first, amplify, then recompress the pulses (usually a grating/prism
combination) with high damage threshhold optics.  This minimizes the number of
high damage optics needed (thus minimizing cost).

Of course, all of this may be done for you, if you buy a complete system.  But
if you are building one, these are the tips that I know of.

To anyone else who may be a "laser jockey", if you check out the latest issue
(APR 19, 99) of Applied Physics Letters, there is an article from a group who
has used a non-collinear optical parametric amplifier to produce ~4.7
femtosecond pulses that are tunable, and actually might be practical for some
ultra-ultrafast spectroscopic applications.  I don't have the exact reference on
me, but if you look in the latest issue, I'm sure you will find it.  On that
note, Clark-MXR (a laser company) has just announced the release of its NOPA,
based on the principles discussed in this article and many preceeding it, that
is capable of less than 30 fsec visible tunable pulses.  Just thought I would
pass these tidbits along.

Till next time,

Jesse Greever

University of Missouri - Columbia

I'm interested to recieve further reports of experiences.
In the futur I will have to work with lasers and discharges and it will be
very interesting for me to know as much as possible.

Right now I'm just new in this lab but I'm very interested in this matter.



Share the wealth!
http://www.ONElist.com
Tell a friend about ONElist's 115,000 free e-mail communities!

Hello all:

Paul...you have asked a very poignant question:  What kind
of information can be obtained for this Photon Echo
experiment?

Well, first of all, I have to say that I am poorly versed in
it as of yet.  I am currently reading Jeffrey Steinfeld's
Book "Molecules and Radiation", a must-read for those
interested in theory of all kinds of spectroscopy.  Right
now, I would estimate, that there are only a handful of four
pulse photon echo setups in the world, and quite honestly,
no one (as far as I know) has unlocked all of the potential
applications.  Presumably, it would tell us something about
the microenvironment around the solute molecule, but it
still a pretty new technique that has not been fully
developed.  I will keep you updated if I find out more.

To everyone, I learned something interesting today...one of
my duties over the next few months will be to construct a
diode pumped, high rep-rate, Nd:YAG (or YLF or YVO) laser.
This will be my first experience at actually building a
laser, so I am very excited, and I think it will be a very
instructive experience.  I propose that when I make some
progress, I might post reports of experiences.  I don't know
if this would be of interest to any of you, but I suspect it
might be.  Let me know if any of you would be interested in
getting periodic progress reports of this experience...if
there only marginal interest, I may setup an auxiliary list
for the few that might be interested, but if there is not
too many objections, then I will post to this list.

Let me say, I am pleased with the growth of this list, and
let's keep the discussions coming.  I have a great feeling
about the potential learning that will take place here.

Till next time,

Jesse Greever

University of Missouri - Columbia

Hi Jesse,

The Bloch equations are indeed the basis of the NMR experiment and many good
texts describe and analyze them. I think the "Bible" for this subject is the
book written by Abragam, "Principles of Nuclear Magnetism", 1961, Oxford
University Press, ISBN 0-19-852014-X.

I also have two good NMR references about these equations which are:
1) P.K. Madhu, A. Kumar, Bloch Equations Revisited: New analytical solutions
for the generalized Bloch equations. Concepts in Magnetic Resonance, 1997,
9(1), 1-12.
2) J.D. Roberts, The Bloch equations. How to have fun calculating what
happens in NMR experiments with a personal computer. Concepts in Magnetic
Resonance, 1991, 3, 27-45.

Of course, you can always go back to the origin of these equations by
looking at the original papers from Felix Bloch.
F. Bloch, Nuclear Induction. Phys. Rev., 1946, 70, 460-474
F. Bloch, W.W. Hansen and M. Packard, The nuclear induction experiment.
Phys. Rev., 1946, 70, 474-485.

Now, if you are interested in the spin echo experiment, the best text to
describe this pulse sequence is from Hahn who discovered the echo principle.
Here is the original paper:
E.L. Hahn. Phys. Rev. 1950, 77, 279.

I hope this will help you get some information to solve your problem. Can
you describe a little bit what you plan to do with the "Four Pulse Photon
Echo Spectroscopy"?

Paul.

Paul Cornillon
Assistant Professor
Purdue University
Whistler Center for Carbohydrate Research
Department of Food Science
1160 Food Science Building
West Lafayette, IN 47907-1160 (USA)
Tel: +1-765-494-1749 Fax: +1-765-494-7953
Email: cornillo@...
Web: http://www.foodsci.purdue.edu/personnel/cornillon.html
----------------------------------------------------------------------------
Hail Purdue!!!

Hi

As I will soon be starting to use a Ti:Sa-laser to excite my molecules, and I
will be doing a lot of the maintainance and tweaking with this thing, I'm
looking for a good book on Ti:Sa-lasers, amplifiers, OPO's and different
experimental techniques used in this field, does anyone now of such a book?

Thanks

Rob

Hello again:

Your friendly moderator here.

Paul...thanks for the post.  I think it is great to see interest from the
application end of spectroscopy as well as interest from the theoretical end. 
Since you are interested in magnetic resonance spectroscopy, I wish to petition
some advice from you.

My graduate work hinges mainly on developing techniques in ultrafast optical
spectroscopy, as well as obtaining dynamic data from molecules in solution.  At
some point, I wish to setup an experiment known as "Four Pulse Photon Echo
Spectroscopy".  This may mean nothing to you at this point, but it centers
around a fundamental equation that is used in a magnetic resonance experiment (I
think it is called Spin Echo or Pulse Echo NMR).  Anyway, the equation that
defines this NMR experiment is the Bloch Equation (I believe), and the great and
wonderful physicist, Richard Feynman, helped develop the Optical Bloch Equation.
I think for my understanding of this theory to begin, I would have to understand
the fundamental Bloch Equation.  Therefore, I was wondering if you might know of
any good texts or articles that might help me understand the intricacies of the
Bloch Equation (of course, I also welcome suggestions from other MR
spectroscopists).

Any help would be greatly appreciated.

Also, does anyone out there know much about Transient Grating Spectroscopy?  It
is more of a curiosity to me than anything else.

Again, thanks to all who have subscribed, and welcome new subscribers (we are
still growing by leaps and bounds).

Happy researching,

Jesse Greever

University of Missouri - Columbia

Hi to all,
I signed up to the list last week. I am interested in NMR spectroscopy and
MRI applied to food science and food engineering. Even though my area of
interest is not general spectroscopy techniques, I am interested in this
group because it will give me other knowledge and physical basis that could
be applied to foods later on.
I am eager to share any experience on my research with any of you and can't
wait to see more things posted on the list.
Great job Jesse for taking the lead of this enterprise.

Paul.

Paul Cornillon
Assistant Professor
Purdue University
Whistler Center for Carbohydrate Research
Department of Food Science
1160 Food Science Building
West Lafayette, IN 47907-1160 (USA)
Tel: +1-765-494-1749 Fax: +1-765-494-7953
Email: cornillo@...
Web: http://www.foodsci.purdue.edu/personnel/cornillon.html
----------------------------------------------------------------------------
Hail Purdue!!!

Hello:

In response to Rob's post, the references that would be helpful would be ones
are found in late 1989 issues of Journal of Physical Chemistry (A?)...

There is a three article series on the development of the technique by Kauffman,
Cote, and Smith (they all worked together, and each one wrote one of the
articles).  The last article came out in early 1990 actually.  The first article
is by Cote, and it goes through the theory and apparatus of the TRFD technique. 
The second is by Kauffman, and it goes through experiments on Fluorene, and the
third is by Smith, and it goes through experiments on p-cyclohexylaniline.  If
you are interseted in Time Resolved Fluorescence Depletion, check them out.  In
the first article, there is a nice theoretical treatment of the technique that
involves time-dependent perturbation theory.  It's a good lesson in
spectroscopy.

Well, that's all I have...till next time.

Jesse Greever

University of Missouri - Columbia

I am a PhD-student at an university in Belgium.  I have graduated as a
physisist last year and I just begon to work on spectroscopy.The purpose of
my studies is plasma spectroscopy.

Hi all,

Well ok I'm in a big hurry, so I'll just quickly sum up the guys that are good
in the business of doing spectroscopy on Van-der-Waals molecules, these
include:
Krausse, Neusser, Muller-Dethleffs, Schlag, Johnson, and some others i don't
remember, but aren't really that important for an overview of the subject.
Btw, these are the last names only. They almost always publish in magazines
such as J. of Chemical Physics or Chem. Phys. Letters.

Adding to what Jesse said about introductions, I think a few refs on your
subject could help clarify your work.

Gotta run, so bye

Rob Satink

Hello all:

Your friendly list moderator here.  The list is growing quite nicely...I get at
least one new subscription per day, and sometimes more.  Just out of pure
curiosity, I would love to hear from those who want to participate in a
introductory "initiation ritual".  For those interested, sometime in the near
future, post your personal research or industrial interests.  I am also curious
to find out who on this list is in the academic sector and who is in the
commercial sector.  Just a quick introductory post will be fine.  Of course, you
do not have to participate in this at all if you do not want to, I just think it
would be nice to hear about other spectroscopist's interests.

Also, for those who might be interested, I found a particularly interesting web
site at:

www.orbitals.com

You can download this interesting little shareware program called the orbital
viewer, and you can get 3-dimensional images of orbitals up to level n=30, l=29.
You can also do LCAO to get hybrid molecular orbitals and construct molecules in
3-D cartesian space.  It is really rather interesting.

Again, welcome to those who are new, and thanks for joining us.

Jesse Greever

University of Missouri - Columbia

Rob:

Would you care to supply the group with some interesting
references about these van der Waals cations that you are
studying?  I am personally not very well read on the
subject, so it might be interesting to read some background
information.

Thanks,

Jesse Greever

University of Missouri

Hi,

I would like introduce myself to you all since i think this mailing list is a
splendid idea. I'm Rob Satink, currently still an undergraduate student, but
soon to become a graduate student at the University of Nijmegen, The
Netherlands. I currently am working for a department in the Science Faculty
called Molecular and Laserphysics. Currently I'm working on the spectrum of an
Van-der-Waals cation, and will continue to study the vibrational structure of
these kind of molecules in my graduate work. I hope I can add to, join, and
enjoy the discussions on this mailing list.

Rob Satink

Hello Spectroscopy Members,

Again, I would like to welcome you to this mailing list, and I hope that
provides a venue for some fascinating discussion.

Currently we have six members, which is extraordinary for only being up for 24
hours.  Please spread the word to other spectroscopists who might be interested
in such a list.

The first item I would like to offer up is:

Is there anyone on this list (besides myself) that is interested in probing
condensed phase dynamics (such as solvation, rotational and vibrational motions
of solutes, etc) using laser spectroscopy?  This is something that I am keenly
interested in, and I would love to hear about different techniques in use right
now.  In our lab, we use a femtosecond Ti:Sapphire Laser System, with a Optical
Parametric Amplifier to provide tunability between 450 and 750 nm. 
Incidentally, the laser was bought from Clark-MXR.  We use a pump-probe setup
(using plane polarized laser pulses) and we use this to perform Time Resolved
Fluorescence Depletion Studies (see papers by Kauffman, Cote and Smith -- 1989).
I do have one problem however...

We populate the first excited state of our molecule with the pump pulse, and
then some delay time later, we send in a probe pulse (right now, at the same
wavelength as the pump), and we monitor the fluorescence depletion at different
delay times of the probe pulse (90 degree fluorescence detection with a
monochromator and PMT).  We are operating at around 10 microjoules per pulse. 
One thing that I am slightly concerned about (since I am still developing this
for condensed phase) is how to account for absorption phenomenon when the probe
pulse interfaces the sample.  We expect for the pulse to stimulate emission,
thereby, depleting the fluorescence, but I also have to take into account
absorption that occurs due to the probe pulse.

Has anybody encountered this in any of their work?  Does anybody have
suggestions.  It is an extremely complex problem.

Anyway, I am glad to see that this group is growing and I am looking forward to
this discussions to come.

Jesse Greever

University of Missouri - Columbia

PS  To post to this list, you can log on to ONElist, follow the link for this
list in the "Member Center" and post the message.  As I have said before, I am
moderating this list, so as to eliminate any junk posts that might come along,
to make this a more efficient list. My one and only rule is that I reserve the
right to ban people from this list who post junk messages (solicitations, links
to porn sites, etc).  This is my one rule, and this is to increase the
productiveness of this list (and not annoy list members).  Thank you to all who
have joined, and I doubt that I will have any problem with this.

Hello to my first few subscribers.

I would like to give a very brief message to everyone, letting you know what my
interests are in the realm of spectroscopy.

I work in an ultrafast (femtosecond) laser lab, and I am interested in probing
very fundamental dynamics using Time Resolved Fluorescence Depletion
Spectroscopy.  We should be able to probe rotational dynamics, vibrational
relaxation and also, we have the setup versatile enough to do other techniques
such as transient absorption, transient grating spectroscopy, and eventually,
four pulse photon echo spectroscopy (see Optical Bloch Equation).

I am in the research group of Dr. John F. Kauffman, the man who co-developed
Time Resolved Fluorescence Depletion.

Anyway, this is the official first post.  Let's keep this list alive with some
stimulating discussion, shall we?

Thanks,

Jesse Greever