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Photodissociation of the ozone molecule at 193.4 nm (6.41 eV) and 157.6 nm (7.87 eV) is studied by fast-beam translational spectroscopy. Coincident detection of the dissociation products allows direct observation of the 3-fragment channel and determination of its kinematic parameters. The results indicate that at each wavelength, 3-fragment dissociation proceeds through synchronous concerted bond breaking, but the energy partitioning among the fragments is different. The branching fraction of the 3-fragment channel increases from 5.2(6)% at 193.4 nm to 26(4)% at 157.6 nm, in agreement with previous studies. It is shown that vibrational excitation of the symmetric stretch mode in O3 molecules created by photodetachment of O- 3 anion enhances the absorption efficiency, especially at 193.4 nm, but does not have a strong effect on the 3-fragment dissociation. [ABSTRACT FROM AUTHOR]

The photodissociation of gas-phase I2Br- was investigated using fast beam photofragment translational spectroscopy. Anions were photodissociated from 300 to 270 nm (4.13-4.59 eV) and the recoiling photofragments were detected in coincidence by a time- and position-sensitive detector. Both two- and three-body channels were observed throughout the energy range probed. Analysis of the two-body dissociation showed evidence for four distinct channels: Br- + I2, I- + IBr, Br+I2-, and I + IBr-. In three-body dissociation, Br(2P3/2) + I(2P3/2) + I- and Br- + I(2P3/2) + I(2P3/2) were produced primarily from a concerted decay mechanism. A sequential decay mechanism was also observed and attributed to Br-(1S)+I2(B3Π0u+) followed by predissociation of I2(B). [ABSTRACT FROM AUTHOR]

The photodissociation of perdeuterated propargyl (D2CCCD) and propynyl (D3CCC) 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: D2 loss, CD+C2D2, and CD3+C2. Observation of the D loss channel was incompatible with this experiment and was not attempted. Our translational energy distributions for D2 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. [ABSTRACT FROM AUTHOR]

The photodissociation of DNCN following excitation of the C 2A″←X 2A″ electronic transition was studied using fast beam photofragment translational spectroscopy. Analysis of the time-of-flight distributions reveals a photodissociation channel leading to D+NCN competitive with the previously observed CD+N2 product channel. The translational energy distributions describing the D+NCN channel are peaked at low energy, consistent with internal conversion to the ground state followed by statistical decay and the absence of an exit barrier. The results suggest a relatively facile pathway for the reaction CH+N2→H+NCN that proceeds through the HNCN intermediate and support a recently proposed mechanism for prompt NO production in flames. [ABSTRACT FROM AUTHOR]

Systematic dissociative photodetachment (DPD) studies of the [I.sub.2.sup.-] and [I.sub.2.sup.-].Ar anions are described. Translational energy distributions for the three-body dissociation channel are similar to the [I.sub.2] distributions and the two-body decay events have shown that little energy is deposited into translation of the photofragments.

Motivated by recent experimental work, a theoretical study of the photodissociation of perdeuterated propargyl (D2CCD) and propynyl (D3CCC) radicals has been carried out, focusing on the C–C bond cleavage and D2loss channels. High-level ab initiocalculations were carried out, and RRKM rate constants were calculated for isomerization and dissociation pathways. The resulting reaction barriers, microcanonical rate constants and product branching ratios are consistent with the experimental findings, supporting the overall mechanism of internal conversion followed by statistical dissociation on the ground state surface. We found loose transition states and very low exit barriers for two of the C–C bond cleavage channels and an additional CD2+ CCD channel, which had not been reported previously. Our results probe the extent of propargyl and propynyl isomerization prior to dissociation at 248 and 193 nm and deliver a comprehensive picture of all ongoing molecular dynamics. [ABSTRACT FROM AUTHOR]

Abstract: The three-body dissociation of (CO2) following excitation of the chromophore to the repulsive A′2Πg,1/2 and electronic states at 1.72 and 3.21eV has been investigated using fast beam photofragment translational spectroscopy. The translational energy distributions for three-body dissociation provide a direct measurement of the CO2 binding energy, yielding a value of 218±10meV. These distributions are vibrationally resolved and show that some CO2 is produced with bend excitation. Dalitz plots show that the dominant three-body decay mechanism is asynchronous–concerted decay, in which the two bond cleavages are distinct but nearly simultaneous events. [Copyright &y& Elsevier]