Kathryn E. Kautzman

Two- and three-body photodissociation of gas phase I3-

The photodissociation dynamics of I3− from 390 to 290 nm (3.18 to 4.28 eV) have been investigated using fast beam photofragment translational spectroscopy in which the products are detected and analyzed with coincidence imaging. At photon energies ⩽3.87 eV, two-body dissociation that generates I−+I2(A 3Π1u) and vibrationally excited I2−(X 2Σu+)+I(2P3/2) is observed, while at energies ⩾3.87 eV, I*(2P1/2)+I2−(X 2Σu+) is the primary two-body dissociation channel. In addition, three-body dissociation yielding I−+2I(2P3/2) photofragments is seen throughout the energy range probed; this is the dominant channel at all but the lowest photon energy. Analysis of the three-body dissociation events indicates that this channel results primarily from a synchronous concerted decay mechanism.

Photofragment coincidence imaging of small I−(H2O)n clusters excited to the charge-transfer-to-solvent state

The photodissociation dynamics of small I-(H2O)n(n=2-5) clusters excited to their charge-transfer-to-solvent (CTTS) states have been studied using photofragment coincidence imaging. Upon excitation to the CTTS state, two photodissociation channels were observed. The major channel (approximately 90%) is a two-body process forming neutral I+(H2O)n photofragments, and the minor channel is a three-body process forming I+(H2O)n-1+H2O fragments. Both processes display translational energy [P(ET)] distributions peaking at ET=0 with little available energy partitioned into translation. Clusters excited to the detachment continuum rather than to the CTTS state display the same two channels with similar P(ET) distributions. The observation of similar P(ET) distributions from the two sets of experiments suggests that in the CTTS experiments, I atom loss occurs after autodetachment of the excited [I(H2O)n-]* cluster or, less probably, that the presence of the excess electron has little effect on the departing I atom.

Photodissociation of the propargyl and propynyl (C3D3) radicals at 248 and 193 nm

The photodissociation of perdeuterated propargyl (D(2)CCCD) and propynyl (D(3)CCC) radicals was investigated using fast beam photofragment translational spectroscopy. Radicals were produced from their respective anions by photodetachment at 540 and 450 nm (below and above the electron affinity of propynyl). The radicals were then photodissociated at 248 or 193 nm. The recoiling photofragments were detected in coincidence with a time- and position-sensitive detector. Three channels were observed: D(2) loss, CD+C(2)D(2), and CD(3)+C(2). Observation of the D loss channel was incompatible with this experiment and was not attempted. Our translational energy distributions for D(2) loss peaked at nonzero translational energy, consistent with ground state dissociation over small (<1 eV) exit barriers with respect to separated products. Translational energy distributions for the two heavy channels peaked near zero kinetic energy, indicating dissociation on the ground state in the absence of exit barriers.