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The infrared spectroscopic profiles of HCOOD/D[sub 2]O mixtures were measured as a function of pressure and concentration. The C–H bond of HCOOD shortens as the pressure is elevated, while the increase in C–H bond length upon diluting HCOOD with D[sub 2]O was observed. Based on the experimental results, the shift in frequency of C–H stretching band is concluded to relate to the mechanism of the hydration of the C–H group and the water structure in the vicinity of the C–H group. The pressure-dependent results can be attributed to the strengthening of C–H---O electrostatic/dispersion interaction upon increasing pressure. The observations are in accord with ab initio calculation forecasting a blueshift of the C–H stretching mode via C–H---O interaction in HCOOD-water/(HCOOD)[sub 2]-(D[sub 2]O) complexes relative to the noninteracting monomer/dimer. Hydrogen-bonding nonadditivity and the size of water clusters are suggested to be responsible to cause the redshift in C–H stretching mode upon dilution HCOOD with D[sub 2]O. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

By using a pump-and-probe technique, we have observed for the first time the product KH formed by reaction of K*(7S) with H2 in a single collision under bulk conditions. In contrast, no detectable laser-induced fluorescence (LIF) signal of KH was detected as the K*(7S) was replaced by the K*(5D), a state having 88 cm-1 less energy. These experiments demonstrate for the first time the possibility for an alkali atom to undergo with the H2 molecule a state-selective reaction. This reaction can be satisfactorily understood in terms of the harpoon mechanism. Measurements of the temperature dependence of the rate constant confirm the proposed mechanism. [ABSTRACT FROM AUTHOR]