Stimulated Emission Pumping: New Methods in Spectroscopy and Molecular Dynamics

Every introductory course in molecular spectroscopy treats the process of assigning spectra as trivial or automatic. At chemically significant levels of vibrational excitation, spectral assignment is certainly not trivial. In fact, the inference of molecular structure from a spectrum may become intrinsically impossible. We deal in this article with spectra far from the textbook limit of small amplitude motions and ask questions of these spectra that are not the traditional ones of equilibrium structure. The task would have been impossible without a technique that offers maximum spectral simplification. In conventional absorption or emission spectroscopy, transitions ema­ nate from a large number of states; thus, the spectra tend to be quite congested and tedious to assign. One is often limited to investigating the low energy region of a particular potential energy surface, usually because this is the only region where transitions are sufficiently strong and the spectra still remain sufficiently free of congestion to be interpretable. The topic of this review, Stimulated Emission Pumping (SEP), is a new.tech­ nique for studying an extraordinarily wide range of rotation-vibration levels in the ground electronic states or other low-lying electronic states of diatomic and small polyatomic molecules. The literature has been covered up to January I, 1 986. SEP is a folded variant of optical-optical double resonancec(OODR),