PHOTODISSOCIATION OF ACETYLENE AT 193.3 NM

The laser-induced fluorescence of H and D products has been used to study the photodissociation dynamics of C2H2, C2D2, HCCD, and CH3CCD at 193.3 nm. The quantum yield for the production of H atoms from acetylene by a one-photon process is determined to be 0.26 +/- 0.04. The average translational energies of D atoms from C2D2 and CH3CCD were 8.0 +/- 1.4 and 9.5 +/- 1.5 kcal/mol. No H atoms were detected as photoproducts of CH3CCD. These facts show that dissociation is faster than internal vibrational redistribution. No anisotropy is found in the Doppler profile as a function of polarization of the photolysis light. The atomic H/D ratio of HCCD is 2.1 +/- 0.2 at 193 nm and 0.93 +/- 0.10 at 157 nm. The low ratio at 193 nm argues against tunneling as a dissociation mechanism.