Enhancement of chargetransfer reaction rate constants by vibrational excitation at kinetic energies below 1 eV J. Chem. Phys. 79, 265 (1983); 10.1063/1.445566Rotational and vibrational energy distributions of 16OH(X 2Π) and 18OH(X 2Π) produced in the reaction of O(1 D) with H2O and H2 18OThe initial vibrational distributions in both energetically accessible channels of the reaction between O( ID) atoms and HCl molecules are reported. The measurements were made using very fast time-resolved Fourier transform spectroscopy to observe the emission spectra of the products before their vibrational populations could be altered by collisional relaxation. Both the OH from the reaction and the HCl created in the E-V energy transfer process have strongly inverted vibrational distributions. The cross section of the former is found to be about 20 times larger than that of the latter. Although spin forbidden, the E-V process is fast, due to the fact that the IA " and 3 A " surfaces of the HOCI intermediate are nearly energetically degenerate over a large region of configuration space. The results suggest that the dynamics of the interaction are dominated by the relatively slow O-Cl collision. The rapid motion of the H atom, in response to changes in the potential created by the motion of the heavier atoms, permits the system to sample the singlet-triplet intersection many times during the collision. OH rotational deactivation is very fast in this system; the average probability for rotational energy transfer in the v' = 3 level is more than four times larger than the gas kinetic collision probability. The time evolution of both vibrational distributions is also reported, and fast v-v energy transfer from vibrationally excited OH to ground state HCI is observed.
Vapor phase room temperature overtone spectra of cyclopropylamine are measured both with conventional absorption spectroscopy for the lower overtones and with intracavity laser photoacoustic spectroscopy for the higher overtones. Spectra are recorded in both the CH-stretching (~vcH=2-7) and NH-stretching (~vNH=2-6) regions. The relative intensities of XH -stretching peaks are explained in terms of the local mode model of harmonically coupled anharmonic oscillators, where all modes but the XH-stretching modes are neglected. The dipole moment function is expanded in the XH-stretching coordinates, with the expansion coefficients determined from ab initio molecular orbital calculations. The high number of peaks throughout the spectra makes assignment difficult, but allows the overlap of spectra from different experimental conditions. Thus it is possible to approximately determine the absolute intensities for the higher overtone spectra that are obtained from the laser experiments. The simple intensity calculation, which contains no adjustable parameters, can account very well for the magnitude of the intensities and for the relative intensities of the pure local mode peaks for all XH oscillators in the overtone spectral region from ~vcH=3 to 7. 5682
The diatomics-in-molecules method has been used to compute potential energy surfaces for the interactions between O(1Dg) atoms and hydrogen molecules, and a multisurface quasiclassical trajectory study of the reaction dynamics for collisions at several different reagent translational energies has been carried out using these potentials. The multisurface nature of the problem was explicitly included by using a surface-hopping computational technique, based on Landau–Zener transition probabilities, which made all of the relevant surfaces available to the trajectory. The product energy distributions predicted by three slightly different DIM models of these surfaces are computed. In all cases, the dynamics of the reactions which begin on the first excited surface are dramatically different from those of reactions which occur on the lowest surface, the only one which was considered in all previous dynamical calculations on this system.
The energy disposal and branching ratios in the reactions of O(1D2) with CHCl3 and CHF3 have been measured using an implementation of time-resolved Fourier transform spectroscopy in this laboratory. The infrared emission from the products of the reactions is measured as a function of time after the creation of the O(1D2) atom by UV photolysis of ozone. The reaction with CHCl3 produces OH, HCl, and CO as primary products. The OH vibrational excitation indicates simple abstraction dynamics. The HCl has much lower vibrational excitation, characteristic of a longer-lived insertion-elimination process, which also produces CO in the decomposition of the internally excited Cl2CO product. Only HF is observed in the reaction with CHF3. In this case the vibrational distribution is nonmonotonic, indicating contributions from two microscopic channels, possibly associated with the formation of F2CO in both the ground (X̃ 1A1) and first excited (Ã 1A2) states.
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