Relaxation from, “higher” vibrational

One more point of importance should be emphasized. Si Ti transitions can take place from higher vibrational substates of Si if vibrational overlap with the vibrational substate of Ti is sufficiently large. The fact, as mentioned earlier, that f iza-state vibrational relaxation to the zero-point vibrational level occurs so rapidly, means that essentially all molecules in Si will be in the zero-point vibrational level. Therefore, radiationless transitions tend to occur from the zero-point vibrational level of the upper electronic state to a higher vibrational substate of the lower electronic state even though vibrational overlap between upper vibrational substates of Si and Ti is good. 

In both cases the vibrational overlap factor is usually close to one so that its effect on can be neglected. This can be seen if we examine Fig. 4. Recall that molecules in excited electronic states such as j are usually found in their j = 0 vibrational substates. This is due to rapid vibrational relaxation from higher substates. Therefore, in electronic emission transitions from the to i electronic states only vibrational transitions of the form (i - 0) need be considered. As can be seen from Fig. 4, the vibrational transition (m -0) has good overlap such that (0 m) will be close to one. 

No dependence of on [Q2] was found for emission from higher vibrational levels of the B state whereas Ix — AtJCh] was found for emission from lower levels. It was concluded that Qj was effective in relaxing higher vibrational levels to lower levels of the B state, and that lower levels were more effectively electronically quenched by chlorine atoms, giving an order < 1 in [Oa] for low vibrational levels. It was argued that the reverse of reaction (8) can occur for higher vibrational levels near the dissociation limit before the product is stabilized by thermonuclear collision to low levels of the B state. 

The general nature of excited singlet relaxation in benzene vapor can be quickly mapped out by reference to the energy level diagram in Fig. 1. Fluorescence is observed only when excitation is limited to the low vibrational regions of shown by the hatched area. Relaxation from higher levels of and from everywhere in and S3 in the vapor is dominated by nonradiative paths. In fact, nonradiative decay is also observed in the low energy r ions of where it competes with fluorescence. Nowhere does fluorescence become the principal relaxation channel. 

A form of radiationless relaxation in which an analyte moves from a higher vibrational energy level to a lower vibrational energy level in the same electronic level. 

Increase of third-body concentration (at constant [Cl]) shifts the emission to the red (emission from lower vibrational levels)128-130 while increase in [Cl] at constant [M] shifts it to the blue (higher levels)128,129. This indicates vibrational relaxation by the third body. The blue shift with increasing [Cl] may be due to the fact that the shortened lifetime of C12(3I70+M), due to (4), allows less time for vibrational relaxation. 

Absorption of light by a fluorescent molecule causes the excitation of an electron moving from a ground state to an excited state (Lakowicz, 1983). After the electron has been excited, it relaxes rapidly from the higher vibrational states to the lowest vibrational state of the excited electronic state after which, the excited state may decay to the ground state by the... 

These authors arrived at a calculated half-width of 150 cm-1, in good agreement with experiment. However, their calculation did not take into account the presence of the as yet unidentified electronic relaxation channel observed by Callomon, Parkin and Lopez-Delgado 9> to be predominant in the radiationless transition from the higher vibrational levels of the lB2u state. This channel may contribute to the broadening in the lB u state. Further extensive photodissociation is observed upon excitation into the state and therefore photodissociation must be considered a possible cause of the line broadening. 

If it is assumed that the crossing between the different substate systems proceeds via an excited vibrational/phonon state, the intensity ratio of the delayed excitation peak relative to the fast one would for that specific vibrational satellite (and presumably all higher lying ones) differ distinctly from the ratio found for the electronic origins. However, such behavior is not observed, at least for vibrational states up to = 1500 cm above the zero-point vibrational levels of the triplet substates. Thus, it can be concluded that the relaxation from an excited vibrational state takes place by a fast process within the individual potential hypersurface of each triplet sublevel to its zero-point vibrational level (intrasubstate relaxation). Subsequently, a comparatively slow sir and/or emission occurs from that electronic state. This result is schematically depicted in Fig. 24. 

The production of OH described here has two features of special interest, being the only case where the vibrational energy is supplied by the electronic energy of an atom and where the proportion of energy appearing as vibration has been estimated. It appears that at least 30% of the OH radicals produced are vibrationally excited and this approximate figure is obtained on the basis that the relative proportions observed do not represent an appreciable relaxation from a state of higher excitation. This appears to be a reasonable assumption in this case, since Reaction 10 may well be faster than relaxation. 

When the nitrosyl halides are flashed, NO is observed in absorption in the y> Sy and c systems at short delays with up to 11 quanta (55 kcal.) of vibrational energy (6, 8). The highest level observed is overpopulated by a factor of 10 and, since the decay of NO is extremely rapid, this probably represents an appreciable relaxation from a situation of an even higher degree of excitation. It is thus evident that the reaction... 

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