On modeling the pressure-dependent photoisomerization of trans-stilbene by including slow intramolecular vibrational energy redistribution.
Experimental data for the photoisomerization of trans-stilbene (S(1)) in thermal bath gases at pressures up to 20 bar obtained previously by Meyer, Schroeder, and Troe (J. Phys. Chem. A 1999, 103, 10528-10539) are modeled by using a full collisional-reaction master equation that includes non-RRKM (Rice-Ramsperger-Kassel-Marcus) effects due to slow intramolecular vibrational energy redistribution (IVR). The slow IVR effects are modeled by incorporating the theoretical results obtained recently by Leitner et al. (J. Phys. Chem. A 2003, 107, 10706-10716), who used the local random matrix theory. The present results show that the experimental rate constants of Meyer et al. are described to within about a factor of 2 over much of the experimental pressure range. However, a number of assumptions and areas of disagreement will require further investigation. These include a discrepancy between the calculated and experimental thermal rate constants near zero pressure, a leveling off of the experimental rate constants that is not predicted by theory and which depends on the identity of the collider gas, the need to use rate constants for collision-induced IVR that are larger than the estimated total collision rate constants, and the choice of barrier-crossing frequency. Despite these unsettled issues, the theory of Leitner et al. shows great promise for accounting for possible non-RRKM effects in an important class of reactions.
Weston
Ralph E
RE
Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973, USA. jrbarker@umich.edu
Barker
John R
JR
D003198:Computer Simulation; D004735:Energy Transfer; D007536:Isomerism; D010777:Photochemistry; D011312:Pressure; D013237:Stereoisomerism; D013267:Stilbenes / Q000737:chemistry*; D014732:Vibration
D013267:Stilbenes