Rotational-Vibrational Spectroscopy

Although it is easier to discuss rotations and vibrations of molecules separately, in reality such motions of molecules occur simultaneously. (Translations are also occurring, and translational motion accounts for a large part of the kinetic energy of a molecule in the gas phase. However, translations do not contribute directly to the topic at hand.) When a sample is in the gas phase, molecules are unhindered in their rotational and vibrational motions, and so both occur simultaneously. In the liquid phase, vibrational motions occur relatively unhindered but rotational motions may be hindered. In the solid phase, vibrations are relatively hindered, and with a few exceptions the rotations are quenched. 

Unless otheiwise noted, all art on this page is Cengage Learning 2014. 

FIGURE 14.35 Complete P and R branches of the rovibrational spectrum of HCl gas. The doublet character of each absorption is due to the natural isotopic abundances of Cl and Cl. 

FIGURE 14.36 Energy -level diagram showing the origin of P and R branches in 

---

This topic covers electron spin resonance (esr) and rotation-vibration spectroscopy. 

Overend J (1975) Rotation Vibration Spectroscopy in the Infrared. In Durig JR (ed) Vibrational Spectra and Structure. Elsevier, Amsterdam Owyoung A (1977) Opt Commun 22 323... 

For decades high-resolution rotational-vibrational spectroscopy treated nuclear motion in terms of near-rigid rotations and small-amplitude vibrations, relying heavily on perturbation theory (FT) [10-16]. While the formulas [11,14,15]... 

F. Moya, S.A.J. Druet, J.P.E. Taran, Rotation-vibration spectroscopy of gases by CARS, in Laser Spectroscopy II, ed. by S. Haroche, J.C. Pebay-Peyroula, T.W. Hansch, S.E. Harris. Springer Notes Phys., vol. 34 (Springer, Berlin, 1975), p. 66... 

Wolfsberg s theoretical researches have focused on a variety of topics including quantum chemistry, isotope effects on thermodynamic properties and on chemical reaction rates, mass-spectrometric fragmentation patterns, translational-vibrational energy transfer, molecular dynamics calculations on condensed phases, and rotational-vibrational spectroscopy. 

In the collinear arrangement the anti-Stokes wave at = 2o)i-(<)2 (w > Wj ) is detected through filters which reject both incident laser beams and also the fluorescence which may be generated in the sample. Figure 8.12 illustrates a typical experimental setup used for rotational-vibrational spectroscopy of gases by CARS [8.50]. The two incident laser beams are provided by a Q-switched ruby laser and a tunable dye laser, pumped by this ruby laser. Because the gain of the anti-Stokes wave depends quadratically on the molecular density N, see (8.33), high power levels of the incident... 

---