Vibrationally relaxed band

Medium effects on the linewidths of electronic transitions are quite pronounced in certain instances. For example, it is quite general that the 0-0 band of an electronic transition will be the sharpest line in the vibronic spectrum of that state. The additional line broadening over that of the 0-0 band usually amounts to 1-5 cm-1, and increases in certain progressions with increasing vibrational separation from the origin. These line broadenings must gauge the vibrational relaxation rates, which are clearly much smaller than the usual rates of electronic relaxation. The assistance... 

It is well known that the v, band of liquid acetonitrile is significantly asymmetric due to an overlap of hot band transitions in the low frequency side. A study of gas phase rotation-vibration spectrum [19] showed that the hot band transition from the first exited state of the degenerated C-C = N bending v8 mode, v hl = v + v8 - vs, has its center at 4.944 cm 1 lower than that of the fundamental transition, v,. Also the presence of v,h2 = v, + 2v8 - 2v8 transition is expected. The careful study on the v band of liquid acetonitrile by Hashimoto et al [20] provided the reorientational and vibrational relaxation times of liquid acetonitrile molecule. They corrected the contribution by the hot band transition using the Boltzmann population law and approximated the v , v,hl, 2h2, and v, + v4 bands by Lorentzian curves. 

Electron bombardment of gas mixtures, although not strictly a photochemical process, has been used in conjunction with time-resolved SS interferometers to obtain rate constants for the vibrational relaxation of highly excited molecules [30, 35, 36, 71-73], Murphy et al. [35,71] observed the production and relaxation of vibrationally excited NO and the (0,0,1 - 0,0,0) bands of N20 and N02 following excitation of N2/02 mixtures with a pulsed electron gun. The infrared emission created by the electron beam decayed completely between pulses and the complete temporal... 

In addition to electronic quenching of the A iBl state, S02 also produces vibrational relaxation in the relatively long lived 3 3 Bt state, as evidenced by the growth of banded emission at the expense of continuum in the 4500 A region when S02 is added. A partial analysis of absorption bands in the 3-% transition has been given230. This transition has also been observed in emission in shock heated S02231 231. ... 

Since the interfacial ET process is faster than the vibrational relaxation, one needs the transition rate from a single molecular vibronic level to the conduction band (or local states coupled to the adsorbed molecule) of the... 

The most important conclusions of these dynamical studies is that van der Waals clusters behave in a statistical manner and that IVR/VP kinetics are given by standard vibrational relaxation theories (Beswick and Jortner 1981 Jortner et al. 1988 Lin 1980 Mukamel and Jortner 1977) and unimolecular dissociation theories (Forst 1973 Gilbert and Smith 1990 Kelley and Bernstein 1986 Levine and Bernstein 1987 Pritchard 1984 Robinson and Holbrook 1972 Steinfeld et al. 1989). One can even arrive at a prediction for final chromophore product state distributions based on low energy chromophore modes. If rIVR tvp [4EA(Ar)i], a statistical distribution of cluster states is not achieved and vibrational population of the cluster does not reflect an internal equilibrium distribution of vibrational energy between vdW and chromophore states. If tvp rIVR, and internal vibrational equilibrium between the vibrational modes is established, and the relative intensities of the Ar = 0 torsional sequence bands of the bare chromophore following IVR/VP can be accurately calculated. A statisticsl sequential IVR/VP model readily explains the data set (i.e., rates, intensities, final product state distributions) for these clusters. 

The strategy we have been following is to pump the v" = 0 - V = 0 vibrational band in the UV and observe the resulting fluorescence. This method reduces complexity caused by eliminating the need to consider vibrational relaxation and results in most of the fluorescence signal appearing in the 0-0 vibrational band. Moreover, the energy levels, transition frequencies and transition probabilities for this band have been studied extensively and can be found in the literature. 

---