Vibrational relaxation rates, anisotropy

HF by HCN. They find that the HF stretch is relaxed by HCN 3.5 times faster than is the C-H stretch of HCN by HF. In view of the fact that the collisional data averages over all orientations, it is not surprising that the difference is smaller than that observed for the complex. What this does suggest, however, is that through the study of the vibrational predissociation of binary complexes it should be possible to determine the orientational dependence of the vibrational relaxation rates. This anisotropy can be very large, as we shall see, and is a quantity which is not available from the collision based experiments. 

The vibrational heating efficiency of LiH molecules in collisions with He atoms was the subject of further study [34], The excitation and relaxation rates over a broad range of temperatures were reported, together with the average energy transfer indices. It was found that in spite of the weak nature of the van der Waals interaction, the strong anisotropy of the surface leads to rovibrational excitation rates which are larger, for example, than those exhibited by the He-CO [35] or He-N2 [36] systems. 

Pulsed two-frequency (ultrafast, femtosecond) polarization-resolved mid-infrared spectroscopy was used in a series of papers by Bakker and coworkers to study the effect of ions on the structural dynamics of their aqueous solutions [44,120]. The solvent consisted of mixtures of Hp and D O (generally O.IM HDO in D O) and the first, the pump, pulse excited the 0-H or 0-D stretch vibration to the first excited state that then relaxed at a measurable rate. The second, the probe, pulse was red-shifted with respect to the first and probed the decay of this excited state. Generally, fairly concentrated electrolyte solutions were required for the application of this technique, in the range 0.5 to lOM. The rotational anisotropy is as follows ... 

This system serves as the prototype for aryl thiyl radicals. Measurements of the high g tensor values and anisotropy observed in ESR [36] was interpreted to indicate a high degree of localization of the unpaired electron on the sulfur atom. This conclusion has been strongly reinforced [37] by experimental observations of a high rate constant for second order decay implying rapid spin relaxation, the formation of diphenyldisulfide as dominant combination product rather than any ring-bonded products and the close similarity of vibrational frequencies in the radical with those of its parent thiophenolate anion and thiophenol species. Further support comes from measurements [38] of the pXg, reduction potential, and electron transfer kinetics. 

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