UV Photodissociation Dynamics of n-Alkyl Bromide

Abstract

Abstract: With the deep development of environmental investigation, some alkyl bromides of higher homolog(e.g., C₂H₅Br, n-C₃H₇Br, n-C₄H₉Br) in the lower stratosphere have attracted a little attention in recent years. But the photodissociation dynamics of them have not been studied. In this work, we reported the photodissociation dynamics of n-alkyl bromides R_Br(R=n-alkyl radical)(C₂H₅Br, n-C₃H₇Br, n-C₄H₉Br) at 234 and_267nm using resonace-enhanced multiphoton ionization (REMPI) with time-flight mass spectrometry(TOF-MS) and the goal was to study the dependencies of the relative quantum yields of φ(Br^*) and φ(Br) on photon energy and the molecular complexity. The measured values of the φ(Br^*) were found to be φ(Br^*)_234nm=0.286 and φ(Br^*)_267nm=0.338 for C₂H₅Br, φ(Br^*)_234nm=0.356 and φ(Br^*)_267nm=0.294 for n-C₃H₇Br, φ(Br^*)_234nm=0.428 and φ(Br^*)_267nm=0.341 for n-C₄H₉Br.The results of φ(Br^*) clearly showed an increasing tendency with the increase of molecular complexity at 234 nm(C₂H₅Br<n-C₃H₇Br<n-C₄H₉Br), while the φ(Br^*) at 267 nm showed a relatively little change. Simultaneously, the φ(Br^*) was found to be strongly dependent on the excitation energy except for C₂H₅Br and showed an increasing tendency with the increase of photon energy[φ(Br^*)_267nm< φ(Br^*)_234nm]. This increasing tendency of φ(Br^*) with the increase of excitation energy was in good agreement with the results observed in photodissociation of n-alkyl iodides.

Key words: n-Alkyl bromide, REMPI-TOFMS, Photodissociation dynamics, Branching ratio

CLC Number:

O644.12

TrendMD:

ZHU Rong-Shu, TANG Bi-Feng, JI Lei, TANG Ying, ZHANG Song, WANG Yan-Mei, ZHANG Bing . UV Photodissociation Dynamics of n-Alkyl Bromide[J]. Chem. J. Chinese Universities, 2004, 25(10): 1885.

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