Collisional energy transfer of highly vibrationally excited NO{sub 2}: The role of intramolecular vibronic coupling and the transition dipole coupling mechanism
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323 (United States)
- Department of Advanced Technology, Brookhaven National Laboratory, Upton, New York 11973 (United States)
The collisional relaxation of highly vibrationally excited NO{sub 2} has been studied for a variety of collision partners (He, Ar, CO, N{sub 2}, O{sub 2}, N{sub 2}O, NO{sub 2}, CO{sub 2}, SF{sub 6}, and toluene) by time-resolved Fourier transform infrared emission spectroscopy. The average energy {l_angle}E{r_angle} of vibrationally excited NO{sub 2} molecules during collisional quenching was obtained from the IR spectra by modeling the {nu}{sub 3} and {nu}{sub 1}+{nu}{sub 3} bands, using the known harmonic frequencies and anharmonicity constants. The average amount of energy lost per collision {l_angle}{Delta}E{r_angle} was determined from the {l_angle}E{r_angle} versus time data. The results show that there is a dramatic increase in the amount of energy transferred for all bath gases at NO{sub 2} energies above 10000{endash}12000cm{sup {minus}1}, which is near the origin of the NO{sub 2} {tilde A}{sup 2}B{sub 2}/{tilde B}{sup 2}B{sub 1} states. This threshold in the energy-transfer rate occurs because of strong vibronic coupling between the {tilde X}{sup 2}A{sub 1} and {tilde A}{sup 2}B{sub 2}/{tilde B}{sup 2}B{sub 1} electronic states. The increase in vibration-to-vibration (V-V) energy transfer can be understood within the context of the transition dipole coupling model. Vibronic coupling in NO{sub 2} produces extensive broadband emission in the IR and near-IR, which enhances the V-V energy-transfer rate by relaxing the resonance conditions in dipole coupling. The V-V energy-transfer probability was calculated using the dipole coupling model, where the transition dipole moment of excited NO{sub 2} was directly extracted from the IR emission spectra. The calculations successfully reproduced the observed threshold in the V-V energy transfer probability. The transition dipole coupling model was also used to estimate the relative contribution of V-V versus vibration-to-translation, rotation (V-T,R) energy transfer for NO{sub 2} deactivation. (Abstract Truncated)
- DOE Contract Number:
- FG02-86ER13484
- OSTI ID:
- 656128
- Journal Information:
- Journal of Chemical Physics, Vol. 107, Issue 8; Other Information: PBD: Aug 1997
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
NITROGEN DIOXIDE
ATOM-MOLECULE COLLISIONS
MOLECULE-MOLECULE COLLISIONS
HELIUM
ARGON
CARBON MONOXIDE
NITROGEN
OXYGEN
NITROUS OXIDE
CARBON DIOXIDE
SULFUR FLUORIDES
TOLUENE
NITROGEN COMPOUNDS
ENERGY TRANSFER
EXCITED STATES
VIBRATIONAL STATES
RELAXATION
EMISSION SPECTRA
DIPOLE MOMENTS
ENERGY-LEVEL TRANSITIONS