Vibrational relaxation of a triatomic molecular impurity: D{sub 2}O in vitreous As{sub 2}S{sub 3}
- Stanford Univ., CA (United States)
- Univ. of Georgia, Athens, GA (United States); and others
Measurements of the relaxation of the D{sub 2}O stretch mode in vitreous As{sub 2}S{sub 3} are presented. Because the bending mode of the molecule offers an intra-molecular decay channel for the stretch mode, the decay scheme of the D{sub 2}O molecule is more complex than that of diatomic molecules. The asymmetric stretch mode of D{sub 2}O has a frequency of 2680 cm{sup -1}. To study the relaxation of this mode we applied a pump-probe technique, using intense psec; pulses of the Stanford Free Electron Laser. Due to the small cross-section of the vibrational mode, successful efforts were made to improve the signal to noise ratio by using a laser stabilization system and a tightly focused beam to increase the intensity, by averaging the signal with a kHz repetition rate and by using samples with an optimized D{sub 2}O concentration. A rapid relaxation rate on the order of 5 x 10{sup 9} sec{sup -1} at low temperature is found that increases with temperature. Recalling that the bending mode of the D{sub 2}O molecule has a frequency of 1170 cm{sup -1}, one would expect a decay in a third order process, involving two quanta of the bending mode plus a vibrational host quanta with a frequency of 340 cm{sup -1}, which coincides with a fundamental frequency of the pyramidal building blocks of the glassy As{sub 2}S{sub 3} host. Instead, we find from the temperature dependence of the relaxation rate that the D{sub 2}O stretching mode relaxes in a higher order process. This indicates that the relaxation dynamics of small molecules is more complex than generally assumed.
- Research Organization:
- Brookhaven National Lab., Upton, NY (United States)
- OSTI ID:
- 238890
- Report Number(s):
- BNL--61982-Absts.; CONF-9508156--Absts.; ON: DE96002729; CNN: Grant N00014-94-1-1024
- Country of Publication:
- United States
- Language:
- English
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