Volome 107. number 6 CHEhllPAL PHYSICS LETTERS 15June1981 zyxwvutsrqp C,(d31-lg) FORMATION IN THE ArF-LASER MULTIPHOTON ABSORPTION OF VINYL CHLORIDE. QUENCHING BY 0, Marta CASTILLEJO, Juan M. FIGUERA and Margarita MARTiN Institute de Quhica F&a ‘Rocasolano ‘: Serrano, I 19, Madrid-6, Spain Received 8 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA February 1984; in final form 5 April 1984 C,(d %I - a3nu) fluorescence is reported following ArF-laser multiphoton absorption of vinyl cl. cr.de nnd 3 possible mechanism 5 or production of Cz(d 3~g) is discussed. The rate constant obtained for removal of C2(d 3n._,) by 02 is (6.1 + 0.85) X IO-” molecule-’ cm3 s-I_ 2 1_ Introduction UV multiphoton absorption of molecules is a use- ful tool to produce excited and ground-state photo- fragments. The kinetics of several radicals and excited species generated in this way have been studied t1--41. ln the case of UV multiphoton dissociation of molecules containing carbon-carbon bonds, a large number of the observed fragmentation channels pre- serve the C-C bond, and several electronic states of the C2 molecule have been observed either by de- tecting their fluorescence or by LIF techniques [Z--5]. While most of the available kinetic data on the C2 molecule are concerned with the a3Hu [2,3,6-IO] and the ground state [4,8-JO], very little informa- tion has been reported concerning the d 311-e state. In the present work we produce the d 3iIp state of C2 in the ArF-laser multiphoton absorption of vinyl chloride, and a Stem-Volmer analysis is carried out to obtain the rate constant for removal of C,(d 3Hg) in the presence of 02_ 2. Experimental The output of a home-made ArF excimer laser * * This laser has been built following the design developed by Dr. C. Webb and coworkers at Clarendon Lab.; see, e.g. ref. [ll]. (ma.ximum output energy of 50 mJ and 1 Hz repeti- tion rate) is focused 5 cm behind the rear window of a fluorescence cell by a 50 cm focal-length specrrosil lens. The fluorescence excited after irradiation of samples of vinyl chloride or vinyl chloride and oxygen is observed at right angles to the laser beam. The flu- orescence is either imaged on the entrance slit of a 0.5 m Jarrell-Ash monochromator and viewed by an EMI 9783B photomultiplier, or collected by a high- intensity Applied Photophysics monochromator and detected by an RCA 1P28 photomultiplier. The pho- tomultiplier signals are collected by a two-channel Datalab transient recorder (DL 922) and displayed on an oscilloscope (Telequipment DlOl 1). Laser energies are measured by a Gen-Tee ED 200 joulemeter. The samples of vinyl chloride have less than 55 of acetylene and ethylene, as measured by gas chromaro- graphy. Mhtures of vinyl chloride and 0, are pre- mixed and stored for several hours prior to use. Pressures are measured wirh MKS Bararron type 22 IA capacitance manometers. 3. Results and discussion 3. I. Production of Cdd 3Hg) Irradiation of 70 mTorr of vinyl chloride by the focused output of the ArF excimer laser gives rise to 0 009-2614/84/S 03.00 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division) 561