FLUENCE AND PRESSURE EFFECTS ON IR MULTIPHOTON DISSOCIATION OF ETHYLBROMIDE

The IR multiphoton dissociation of C2H5Br was studied as a function of the laser fluence and substrate pressure using a pulsed TEA CO2 laser at the 10P(20) (10.59 mum, 944 cm-1) laser line. The effects of added H-2, He, N2 and NO were also studied. The reaction products were foun d to be C2H2, C2H4, C2H6 and CH4. The increase in the partial pressure of the products with increasing substrate pressure was interpreted in terms of the large contribution from a collision-induced reaction bet ween the reactant molecules excited below the reaction threshold. At a focal fluence of less than 100 J cm-2, C2H4 was the only reaction pro duct detected, whereas C2H2 and CH4 also appeared at higher fluence. T he formation of C2H2 and CH4 at higher fluence was attributed to addit ional laser photon absorption by vibrationally excited ethylene (C2H4 ) primarily in the quasi-continuum state. The production of C2H6 was d ue to C-Br bond fission. The observed dissociation data were compared with the theoretical predictions obtained using the energy-grained mas ter equation.