Nascent OHX 2 P) product state distributions from the reaction of O 1 D) with ethylene. A laser-induced ¯uorescence study Miguel Gonz alez a, * , Mar  õa P. Puyuelo b , Jordi Hernando a , Rodrigo Mart  õnez b , R. Say os a , Pedro A. Enr  õquez b a Departament de Qu  õmica F  õsica, Centre de Recerca en Qu  õmica Te  orica, Universitat de Barcelona, Mart  õ i Franqu es, 1. 08028 Barcelona, Spain b Departamento de Qu  õmica, Universidad de La Rioja, Madre de Dios, 51. 26004 Logro~ no, Spain Received 5 April 2001; in ®nal form 14 August 2001 Abstract The full characterization of the OHX 2 P, v 00  0±3, N 00 , J 00 , K 00 ) product state distributions for the O 1 D C 2 H 4 ! OH  C 2 H 3 reaction was experimentally performed using the laser-induced ¯uorescence LIF) technique. Statistical spin±orbit distributions were obtained, while some preference for the formation of the PA 0  K-doublet level was observed. The rovibrational populations obtained suggest that the reaction preferentially evolves via insertion, yielding rovibrationally cold OH through slow decomposition of an alcohol-type collision complex and rovibrationally excited OH by fast decomposition. Moreover, some evidences were found about the implication of an abstraction mechanism, which would produce rotationally cold and highly vibrationally excited OH. Ó 2001 Elsevier Science B.V. All rights reserved. 1. Introduction The reactions of the oxygen atom in the ®rst excited electronic state, O 1 D), with hydrocarbons are relevant in stratospheric chemistry, since they participate in the ozone degradation processes through the OH=HO 2 catalytic cycle [1±3]. Previ- ous experimental studies on the energetics of the OH product arising from these reactions focused mainly on the O 1 D)+alkane reactions [4±9]. From the results obtained, it was suggested that this kind of reactions evolve through insertion of the oxygen atom into a C±H bond followed by the dissociation of the alcohol-type collision complex formed. These conclusions are also supported by the results of experiments on the stereodynamics of these reactions [10±13] and dynamics calcula- tions [14,15]. In contrast, the properties of the products of the reactions between O 1 D) and non-saturated hy- drocarbons have been barely analyzed. Here, an experimental study of the following reaction has been performed: O 1 D C 2 H 4 ! OHX 2 P C 2 H 3 DH 0 298 K 39:7 kcal mol 1 1 28 September 2001 Chemical Physics Letters 346 2001) 69±80 www.elsevier.com/locate/cplett * Corresponding author. Fax: +34-93-4021231. E-mail address: miguel@qf.ub.es M. Gonz alez). 0009-2614/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S0009-261401)00953-8