I have the answer to a couple of your questions:

1. The reason you used quartz rather than glass when doing UV
spectroscopy is that normal glass cells generally do not transmit
anything below 300 nm (give or take). Quartz is transparent for
most of the normal UV range (not sure about XUV...probably not).

2. The microwave frequency used by domestic microwaves corresponds
to a ROTATIONAL transition in water, not vibrational. The
vibrational transitions are infrared transitions.


Hope that answers a few of your queries.

Jesse