Infrared multiphoton induced isomerization ofcishyphen;3,4hyphen; dichlorocyclobutene. I. Experimental results

摘要

The yield and product distribution in the laserhyphen;induced isomerization ofcishyphen;3,4hyphen;dichlorocyclobutene (DCCB) have been measured as functions of laser fluence, DCCB pressure, and buffer gas pressure. Both Woodwardndash;Hoffman allowed and lsquo;lsquo;forbiddenrsquo;rsquo; isomers were observed. The fraction of lsquo;lsquo;forbiddenrsquo;rsquo; products was found to increase linearly with fluence above a threshold of 3.5 J/cm2. At high fluence the yield increased quadratically with neat DCCB pressure. Both the yield and fraction of lsquo;lsquo;forbiddenrsquo;rsquo; products declined monotonically with buffer gas pressure. These observations are explained in terms of a twohyphen;channel mechanism, in which the allowed isomer is formed in a concerted path and the forbidden isomers are produced from a diradical intermediate in a nonconcerted reaction.