Hi Varathu,

There are lots of good books on spectroscopy which can give you a great
deal of information about the questions you are asking.

http://www.wiley.com/WileyCDA/WileyTitle/productCd-0471974218.html (High
Resolution Spectroscopy, Second Edition
J. Michael Hollas)

Anyway, it has do with the derivation of the selection rules for these
spectroscopies.

In IR, if you look at the basic eqaution of the transition moment
integral, we have dipole moment in it. This term is then expanded. After
applying the orthogonality theorem, one gets the selection rules for IR
which says that the dipole moment has to change along that coordinate. I
am sure you may not want to go into details unless and until you are
really after something. I guess the convention is to accept these
selection
rules (rules which define why we see some peaks in spectra and why not
other).

The answer for MW is also similar.

I hope Ms. Vandana will agree with this answer.

Thanks

- Rahul

Purdue University,
West Lafayette, IN 47907

*************************************************************************
On Sat, 3 Jul 2004, [iso-8859-1] varathu rajan wrote:

> Dear Madam,
> My question is why a molecule should have permanent dipole moment to
absorb the Micro Wave radiation.
> In other words why molecules such as Hydrogen does not give rotational
spectra?
> Similarly why symmetrical stretching of CO2 is Infrred inactive?
>
> Friendly,
> Varathu.
>
> Vandana Sharma <vandanas@...> wrote:
> Dear Varathu,
>
> Could you please elaborate your question.
>
> Regards,
> Vandana
>
>
> Vandana Sharma
> Research Scholar
> Laboratory Astrophysics,
> LAB- 570
> Space and Planetary Atmosphere Division,
> Physical Research Laboratory,
> Navrangpura,
> Ahmedabad- 380 009
> Gujarat, India
>
> Phone No : (91)-079-6302129-Ext-4570/4567(lab)
> Email : vandanas@...
> van_res@...
> URL : http://www.prl.ernet.in/~vandanas
>
> On Thu, 24 Jun 2004, [iso-8859-1] varathu rajan wrote:
>
> > Dear Friends,
> >
> > I have a dobt in the fundamentals of spectrosopy.
> > My doubt is
> > 1.For a molecule to be MW active,why it should have permanent Dipole moment
&.
> > 2.To be IR active, why a molecule should undergo net change in its dipole
moment?
> >
> > Plz clear my doubts
> >
> > Friendly,
> > Varathu
> >
> >
> >
> > Yahoo! India Matrimony: Find your partner online.
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