文档介绍：7. The CO Sideband Spectrometer
The Experimental Setup
A chemically important frequency region is the region of the carbonylic
stretch (1600–2100 cm−1). So far, spectroscopic studies have been restricted
to the resolution of lead salt diode lasers (50–100 MHz). However, the use of
nonlinear frequency mixing of a finely tunable CO laser with microwave radi-
ation allows the generation of narrow (< 300 kHz) IR radiation which can be
used for high-resolution spectroscopy plexes. The overall experimental
setup of a such a spectrometer is shown in Fig. . The spectrometer consists
of ponents, which will be described individually below.
The CO Laser
The CO laser is a gas discharge laser with a high efficiency in the infrared
region. The first laser activity was observed in 1965 by Patel [152]. The
laser emits radiation from numerous vibrational–rotational transitions of the
CO molecule. The pumping of populations into higher vibrational states is
achieved via electronic excitation and the so-called “anharmonic vibration–
vibration pumping”. This process was studied for the first time by Treanor
and Rich [192]. A partial population inversion is found for P transitions be-
tween adjacent vibrational levels, and laser emission can be achieved in the
region from 1200 to 2100 cm−1. The laser line width is less than 300 kHz. It
is also possible to stabilize the CO laser using optogalvanic lamp dips [175].
An overview of recent results in CO laser development and its spectroscopic
applications has been given by Urban [193, 194]. An extension of the avail-
able frequency region of the CO laser was plished by the development
of the CO overtone laser by Urban and coworkers [64]. Laser emission could
then be achieved for overtone (. ∆v = 2) transitions in the region between
2500 and 3800 cm−1(for details see [4]). The spacing between nearby laser
transitions is limited by the rotational spacing between adjacent J levels in
CO, which amounts to ca.