VIBRATIONAL-EXCITATION OF H2O AND HOD MOLECULES PRODUCED BY REACTIONSOF OH AND OD WITH CYCLO-C6H12, N-C4H10, NEO-C5H12, HCL, DCL AND NH3 AS STUDIED BY INFRARED CHEMILUMINESCENCE

The room-temperature reactions of OH(OD) radicals with cyclo-C6H12, n- C4H10, and neo-C5H12 have been investigated by observing the infrared chemiluminescence from the H2O(HOD) molecules generated in a fast-flow reactor. These hydrocarbon molecules are representative for abstracti on from secondary and primary C-H bonds. The total vibrational energy released to H2O(HOD) was in the range of [f(v)]=0.55-0.65. The majorit y (80%-85%) of the vibrational energy is in the stretching modes and t he main energy release is to the local mode associated with the new OH bond. The dynamics associated with the energy disposal to H2O(HOD) re semble the H+L-H dynamics for the analogous reactions of F atoms. The data from H2O and HOD are complementary because of the different colli sional coupling between the energy levels of the nu(1), nu(2), and nu( 3) modes; however, no specific isotope effect was found for the energy disposal to H2O versus HOD for reactions with the hydrocarbon molecul es. In contrast, a very unusual isotope effect was found between the O H+HCl and OD+HCl pairs. The latter reaction gave the expected stretchi ng mode excitation of HOD; however, the OH reaction gave H2O molecules with virtually no vibrational energy. This anomalous situation is par tly associated with an inverse secondary kinetic-isotope effect, but t he main isotope effect is on the dynamics of the energy disposal proce ss itself. (C) 1998 American Institute of Physics.