H ATOM FORMATION DYNAMICS IN THE DISSOCIATION OF CH3-CF2CL (HCFC-142B) AFTER UV AND VUV LASER PHOTOEXCITATION

Using the laser photolysis/laser-induced fluorescence (LIF) ''pump-and -probe'' technique, the dynamics of H atom formation in the photodisso ciation of CH3-CF2Cl (HCFC-142b) after excitation at 193 nm-and the Ly man-alpha wavelength were studied under collision-free conditions in t he gas-phase at room temperature. The H atoms produced were detected b y (2p(2)P<--1s(2)S)-LIF using tunable narrow-band Lyman-alpha laser ra diation (lambda(La)approximate to 121.6 nm) generated by resonant thir d-order sum-difference frequency conversion of pulsed dye laser radiat ion. In the VUV photodissociation experiments the Lyman-alpha laser ra diation was used both to photodissociate the parent molecules and to d etect the produced nascent H atoms via laser induced fluorescence. The following: quantum yields Phi(H) for H atom formation were determined by a photolytic calibration method: Phi(H)(193 nm)=(0.06+/-0.02) and Phi(H)(L-alpha,)=(0.53+/-0.12). From the measured H atom Doppler profi les the average H atom kinetic energy was determined to be ET(193 nm)= (51+/-10) kJ/mol and E-T(L-alpha)=(72+/-4) kJ/mol, respectively. (C) 1 997 American Institute of Physics.