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Singly and doubly charged scandium-water ion-molecule complexes are produced in a supersonic molecular beam by laser vaporization. These ions are mass analyzed and size selected in a specially designed reflectron time-of-flight spectrometer. To probe their structure, vibrational spectroscopy is measured for these complexes in the O-H stretching region using infrared laser photodissociation and the method of rare gas atom predissociation, also known as 'tagging.' The O-H stretches in these systems are shifted to lower frequency than those for the free water molecule, and the intensity of the symmetric stretch band is strongly enhanced relative to the asymmetric stretch. These effects are more prominent for the doubly charged ions. Partially resolved rotational structure for the Sc+(H2O)Ar complex shows that the H-O-H bond angle is larger than it is in the free water molecule. Fragmentation and spectral patterns indicate that the coordination of the Sc2+ ion is filled with six ligands (one water and five argons). [ABSTRACT FROM AUTHOR]

The CH fragment from the 193 nm photodissociation of CHCl is observed in a molecular beam experiment. This fragment is formed in the higher-energy dissociation pathway, the lower pathway involving formation of CCl. Both the CHCl parent molecule and the CH fragment were detected by laser-induced fluorescence. The 193 nm CHCl absorption cross section was estimated from the reduction of the CHCl signal as a function of the photolysis laser fluence. The CH internal state distribution was derived from the analysis of laser-induced fluorescence spectra of the A-X Δv=0 sequence. A modest degree of rotational excitation was found in the CH fragment; the most probable rotational level is N=1, but the distribution has a tail extending to N>25. Also observed is a slight preference for formation of Λ-doublets of A″ symmetry, which appears to increase with increasing rotational angular momentum N. Vibrationally excited CH was observed, and the degree of vibrational excitation was found to be low. The energy available to the photofragments is predominantly released as translational excitation. The preferential formation of A″ Λ-doublets suggests that dissociation occurs through a nonlinear excited state. [ABSTRACT FROM AUTHOR]

The dynamics of the 193 nm photodissociation of the CCl2 molecule have been investigated in a molecular beam experiment. The CCl2 parent molecule was generated in a molecular beam by pyrolysis of CHCl3, and both CCl2 and the CCl photofragment were detected by laser fluorescence excitation. The 193 nm attenuation cross section was estimated from the reduction of the CCl2 signal as a function of the photolysis laser fluence. The internal state distribution of the CCl photofragment was derived from analysis of laser fluorescence excitation spectra in the A 2Δ-X 2Π band system. Most of the energy available to the CCl(X 2Π)+Cl fragments appears as translational energy. The CCl fragment rotational energy is much less than predicted in an impulsive model. The excited electronic state appears to dissociate indirectly, through coupling with a repulsive state arising from the ground-state CCl(X 2Π)+Cl asymptote. The identity of the initially excited electronic state is discussed on the basis of what is known about the CCl2 electronic states. [ABSTRACT FROM AUTHOR]

Molecule–surface collision-induced dissociation (CID) has been studied for n-C3F7NO and i-C3F7NO molecular beams scattered from MgO(100) at incident kinetic energies (Eincident) up to 7 eV. The NO fragment was detected state selectively using two-photon, two-frequency ionization, and rotational and spin–orbit distributions are reported for several Eincident values. State and angle-resolved signals were integrated to give CID yields, which increased sharply with Eincident . In most cases, rotational excitation could be described by separate temperatures for each spin–orbit state. The upper 2∏3/2 state was underpopulated relative to statistical predictions (e.g., for n-C3F7NO at Eincident =5.0 eV, the spin–orbit temperature was ∼170 K, while Trot was ∼500 K). The CID results are compared to NO state distributions derived from the photodissociation of expansion-cooled molecules under collision-free conditions, at different energies (E°) above D0. These distributions were measured for both n-C3F7NO and i-C3F7NO up to E°∼4500 cm-1, and rotational excitation within each spin–orbit state was statistical, except at E°≥3000 cm-1. As with CID, a low [2∏3/2]/[2∏1/2] ratio was observed, and the reaction mechanism is probably unimolecular decomposition via the lowest triplet surface T1 with little or no exit channel barrier. The pronounced similarities between the CID and photodissociation results suggest that common reaction mechanisms may be operative. All of the CID results are compatible with direct inelastic scattering followed by unimolecular reaction on the S0 and/or T1 potential surfaces. [ABSTRACT FROM AUTHOR]

M(CH3)2 (M=Zn,Cd) vapor was photodissociated at 193 nm into CH3 and MCH3 (A 2E) radicals and also into CH3 radicals and M atoms. The kinetic energy distribution of the CH3 was measured by a molecular beam time of flight technique. The emission spectrum of the MCH3(A 2E) was recorded in the visible region (for the first time) and it was shown that the radicals were vibrationally cold. An excitation spectrum for visible emission was determined through the VUV region down to 125 nm. Two photon production of M(n 3P01 ) states was easily observable but shown to be negligible compared to one photon processes. The methyl radicals released in this dissociation are slower but vibrationally hotter than those dissociated from CH3I. [ABSTRACT FROM AUTHOR]