Fast beam photodissociation studies of small molecules by time- and position-sensitive coincident imaging.

摘要

Photodissociation studies of anions and radicals are carried out using the technique of fast beam photofragment spectroscopy. Coincidence measurements of the photofragments' arrival times and positions for each dissociation event permit the calculation of photofragment mass distributions. Translational energy distributions (P(ET)) are also calculated for each product channel. Substantial information regarding the potential energy surface responsible for dissociation and dynamic information about the decay mechanism for each decay process are obtained.; The photodissociation dynamics of I-(H2O) n (n=2-5) clusters excited to their charge-transfer-to-solvent (CTTS) states have been investigated. Upon excitation to the CTTS state, two photodissociation channels were observed. The major channel is a two-body process forming I+(H2O)n photofragments, and the minor channel is a three-body process forming I+(H2O) n-1+H2O fragments. Both processes display P(ET) distributions peaking at ET=0. Clusters excited to the detachment continuum rather than to the CTTS state display the same channels with similar P(ET) distributions. This observation suggests that in the CTTS experiments, I atom loss occurs after autodetachment of the excited [I(H2O)n-]* cluster.; Systematic dissociative photodetachment (DPD) studies of the I2 - and I2-·Ar anions in the region 4.24-4.78 eV are presented. Photofragment mass distributions and P(ET) distributions from the DPD of I2- are described and facilitate understanding of the IrAr system. For the IrAr complex, channels resulting from two-body dissociation leading to I2 +Ar photoproducts are observed at all photon energies employed, and we report the first direct observation of the three-body dissociation channel leading to I+I+Ar photoproducts. The relative intensities of each decay channel are investigated relative to the electronic state being accessed. P(E T) distributions of the IrAr complex lend further insight into the decay mechanism for each channel. This work has also lead to the correction of the previously misassigned photoelectron spectrum of I2-.; Preliminary dissociation experiments performed on the C3H 3 radical at 6.42 eV are also presented. These experiments show the presence of a dissociation channel corresponding to methyl loss for the propynyl isomer, and a small channel corresponding to CH-loss is apparent for the propargyl isomer.; The construction, and characterization of a new ionization source based on the Even-Lavie valve are also described.