Fluence and pressure effects on IR multiphoton dissociation of ethylbromide

Abstract

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) (10.59μm,944 cm−1) laser line. The effects of added H2, He, N2 and NO were also studied. The reaction products were found to be C2H2, C2H4, C2H6 and CH4. The increase in the partial pressure of the products with increasing sustrate pressure was interpreted in terms of the large contribution from a collision-induced between the reactant molecules excited below the reaction threshold. At a focal fluence of less than 100 J cm−2, C2H4 was the only reaction product detected, whereas C2H2 and CH4 also appeared at higher fluence. The formation of C2H2 and CH4 at higher fluence was attributed to additional laser photon absorption by vibrationally excited ethylene (C2H4*) primarily in the quasi-continuum state. The production of C2H6 was due to CBr bond fission. The observed dissociation data were compared with the theoretical predictions obtained using the energy-grained master equation.