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IR photodissociation (IRPD) spectra of (N2O)2+•Ar and (N2O)n+ with n=3–8 are measured in the 1000–2300 cm-1 region. The (N2O)2+•Ar ion shows an IRPD band at 1154 cm-1, which can be assigned to the out-of-phase combination of the ν1 vibrations of the N2O components in the N4O2+ ion; the positive charge is delocalized over the two N2O molecules. The geometry optimization and the vibrational analysis at the B3LYP/6-311+G* level show that the N4O2+ ion has a C2h structure with the oxygen ends of the N2O components bonded to each other. The IRPD spectra of the (N2O)n+(n=3–8) ions show three prominent bands at ∼1170, ∼1275, and ∼2235 cm-1. The intensity of the ∼1170 cm-1 band relative to that of the other bands decreases with increasing the cluster size. Therefore, the ∼1170 cm-1 band is ascribed to the N4O2+ dimer ion core and the ∼1275 and ∼2235 cm-1 bands are assigned to the ν1 and ν3 vibrations of solvent N2O molecules, respectively. Since the band of the N4O2+ ion core is located at almost the same position for all the (N2O)n+(n=2–8) clusters, the C2h structure of the dimer ion core does not change so largely by the solvation of N2O molecules, which is quite contrastive to the isoelectronic (CO2)n+ case. [ABSTRACT FROM AUTHOR]

Transient grating (TG) spectroscopy has been applied to the photoinduced hydrogen-abstraction reaction of benzophenone (BP) in various kinds of room temperature ionic liquids (RTILs). After the photoexcitation of BP in RTILs, the formation of a benzophenone ketyl radical (BPK) was confirmed by the transient absorption method, and the TG signal was analyzed to determine the diffusion coefficients of BPK and BP. For comparison, diffusion coefficients of carbon monoxide (CO), diphenylacetylene (DPA), and diphenylcyclopropenone (DPCP) in various RTILs were determined by the TG method using the photodissociation reaction of DPCP. While the diffusion coefficients of the stable molecules BP, DPA, and DPCP were always larger than those predicted by the Stokes–Einstein (SE) relation in RTILs, that of BPK was much smaller than those of the stable molecules and relatively close to that predicted by the SE relation in all solvents. For the smallest molecule CO, the deviation from the SE relation was evident. The diffusion coefficients of stable molecules are better represented by a power law of the inverse of the viscosity when the exponent was less than unity. The ratios of the diffusion coefficient of BP to that of BPK were larger in RTILs (2.7–4.0) than those (1.4–2.3) in conventional organic solvents. The slow diffusion of BPK in RTILs was discussed in terms of the fluctuation of the local electric field produced by the surrounding solvent ions. [ABSTRACT FROM AUTHOR]

An experimental technique based on a scheme of vibrationally mediated photodissociation has been developed and applied to the spectroscopic study of highly excited vibrational states in HCN, with energies between 29 000 and 30 000 cm-1. The technique consists of four sequential steps: in the first one, a high power laser is used to vibrationally excite the sample to an intermediate state, typically (0,0,4), the ν[sub 3] mode being approximately equivalent to the C–H stretching vibration. Then a second laser is used to search for transitions between this intermediate state and highly vibrationally excited states. When one of these transitions is found, HCN molecules are transferred to a highly excited vibrational state. Third, a ultraviolet laser photodissociates the highly excited molecules to produce H and CN radicals in its A [sup 2]Π electronic state. Finally, a fourth laser (probe) detects the presence of the CN(A) photofragments by means of an A→B→X laser induced fluorescence scheme. The spectra obtained with this technique, consisting of several rotationally resolved vibrational bands, have been analyzed. The positions and rotational parameters of the states observed are presented and compared with the results of a state-of-the-art variational calculation. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The photodissociation dynamics of ICN to CN+I(2P3/2) are investigated by state selective one-dimensional photofragmentation translation spectroscopy at 304.67 nm. Translational energy release, laboratory anisotropy factors, and energy distributions are obtained from analysis of the velocity and spatial distributions of the photodissociated iodine atoms. Two velocity distributions peaks are deconvoluted which are found to be separated by 2000 cm-1, which is the CN stretching vibration of the CN radical. The high intensity velocity peak is assigned to dissociation to I+CN(X 2Σ+) in v=0 (channel I), while the weak lower velocity peak is attributed to dissociation to I+CN(X 2Σ+) in v=1 (channel II). More than 80% of the iodine are produced from channel I and are found to have a relatively small anisotropy parameter, β, that is independent of velocity, suggesting a mixed absorption polarization leading to rapid dissociation. The weak shoulder, representing less than 20% of the photodissociated iodine, is formed via channel II and found to have a β value that decreases with velocity and produces CN with more of the available excess energy appearing in rotation, suggesting longer dissociation time that allows for more energy redistribution prior to dissociation. The dissociation mechanisms involved in these two channels are discussed in terms of these results, the theoretically predicted properties of the 3Π+0 and 3Π1 surfaces of ICN, our previous conclusion that suggests that ICN bends prior to dissociation via channel II, the laser wavelength used, and curve crossing between the 3Π+0 and 1Π1 surfaces. [ABSTRACT FROM AUTHOR]

Mg+–H2O ion–molecule complexes are produced in a pulsed supersonic nozzle cluster source. These complexes are mass selected and studied with laser photodissociation spectroscopy in a reflectron time-of-flight mass spectrometer system. An electronic transition assigned as 2B2←X 2A1 is observed with an origin at 28 396 cm-1. The spectrum has a prominent progression in the metal-H2O stretching mode with a frequency (ω’e) of 518.0 cm-1. An extrapolation of this progression fixes the excited state dissociation energy (D’0) at 15 787 cm-1. The corresponding ground state value (D‘0) is 8514 cm-1 (24.3 kcal/mol). The solvated bending mode, and symmetric and asymmetric stretching modes of water are also active in the complex, as are the magnesium bending modes. A second electronic transition assigned as 2B1←X 2A1 is observed with an origin at 30 267 cm-1 and a metal stretch frequency for Mg+–H2O of 488.5 cm-1 (ΔG1/2). Spectra of both excited states are also observed for Mg+–D2O. Partially resolved rotational structure is analyzed for both isotopes, leading to the conclusion that the complex has a structure with C2v symmetry. This study was guided by ab initio calculations by Bauschlicher and co-workers, which provide accurate predictions of the electronic transition energies, vibrational constants, and dissociation energies. [ABSTRACT FROM AUTHOR]