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Photodissociation Study of Ethyl Bromide in the Ultraviolet Range by the Ion‐Velocity Imaging Technique
Author(s) -
Tang Ying,
Ji Lei,
Zhu Rongshu,
Wei Zhengrong,
Zhang Bing
Publication year - 2005
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200500246
Subject(s) - photodissociation , chemistry , atomic physics , ion , excited state , wavelength , bromide , bromine , ionization , recoil , molecular physics , physics , optics , photochemistry , organic chemistry
The photodissociation of ethyl bromide has been studied in the wavelength range of 231–267 nm by means of the ion velocity imaging technique coupled with a [2+1] resonance‐enhanced multiphoton ionization (REMPI) scheme. The velocity distributions for the Br ( 2 P 1/2 ) (denoted Br*) and Br ( 2 P 3/2 ) (denoted Br) fragments are determined, and each can be well‐fitted by a narrow single‐peaked Gaussian curve, which suggests that the bromine fragments are generated as a result of direct dissociation via repulsive potential‐energy surfaces (PES). The recoil anisotropy results show that β (Br) and β (Br*) decrease with the wavelength, and the angular distributions of Br* suggest a typical parallel transition. The product relative quantum yields at two different wavelengths are Φ 234nm (Br*)=0.17 and Φ 267nm (Br*)=0.31. The relative fractions of each potential surface for the bromine fragments’ production at 234 and 267 nm reveal the existence of a curve crossing between the 3 Q 0 and 1 Q 1 potential surfaces, and the probability of curve crossing decreases with the laser wavelength. The symmetry reduction of C 2 H 5 Br from C 3 v to C s invokes a nonadiabatic coupling between the 3 Q 0 and 1 Q 1 states, and with higher energy photons, the probability that crossing will take place increases.