We present a theoretical study of the unimolecular dissociation resonances of HCO in the electronic ground state, X 1 AЈ, using a new ab initio potential energy surface and a modification of the log-derivative version of the Kohn variational principle for the dynamics calculations. Altogether we have analyzed about 120 resonances up to an energy of Ϸ2 eV above the HϩCO threshold, corresponding to the eleventh overtone in the CO stretching mode (v 2 ϭ11). The agreement of the resonance energies and widths with recent stimulated emission pumping measurements of Tobiason et al. ͓J. Chem. Phys. 103, 1448 ͑1995͔͒ is pleasing. The root-mean-square deviation from the experimental energies is only 17 cm Ϫ1 over a range of about 20 000 cm Ϫ1 and all trends of the resonance widths observed in the experiment are satisfactorily reproduced by the calculations. The assignment of the states is discussed in terms of the resonance wave functions. In addition, we compare the quantum mechanical state-resolved dissociation rates with the results of classical trajectory calculations and with the predictions of the statistical model.

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Three-dimensional quantum mechanical calculations have been carried out, using a modification of the log-derivative version of Kohn’s variational principle, to study the dissociation of HO2 into H and O2. In a previous paper, over 360 bound states were found for each parity, and these are shown to extend into the continuum, forming many resonant states. Analysis of the bound states close to the dissociation threshold have revealed that HO2 is a mainly irregular system and in this paper it is demonstrated how this irregularity persists in the continuum. At low energies above the threshold, these resonances are isolated and have widths that fluctuate strongly over more than two orders of magnitude. At higher energies, the resonances begin to overlap, while the fluctuations in the widths decrease. The fluctuations in the lifetimes and the intensities in an absorption-type spectrum are compared to the predictions of random matrix theory, and are found to be in fair agreement. The Rampsberger–Rice–Kassel–Marcus (RRKM) rates, calculated using variational transition state theory, compare well to the average of the quantum mechanical rates. The vibrational/rotational state distributions of O2 show strong fluctuations in the same way as the dissociation rates. However, their averages do not agree well with the predictions of statistical models, neither phase space theory (PST) nor the statistical adiabatic channel model (SACM), as these are dependent on the dynamical features of the exit channel. The results of classical trajectory calculations agree well on average with those of the quantum calculations.

The usual theoretical procedure for evaluating the di †erential cross section (DCS) of a molecular collision consists of numerically summing a partial wave series (PWS) for the scattering amplitude. The PWS typically has many numerically signiÐcant terms making it difficult (or impossible) to gain physical insight into the origin of structure in a DCS. A nearsideÈfarside (NF) analysis of a DCS decomposes the PWS scattering amplitude into two subamplitudes : one nearside, the other farside. This decomposition is successful if the magnitudes of the two subamplitudes are never much greater than that of the scattering amplitude itself. It is then often possible to gain a clear physical picture of the origin of structure in a DCS, and hence obtain information on the collision dynamics. A new NF theory called the restricted NF decomposition is described. We present the Ðrst application of this NF decomposition to reactive molecular collisions whose PWS are expanded in a basis set of reduced rotation matrix elements. The reactions whose DCSs we NF analyze are :] HD ] D. matrix elements are employed as input to the NF analyses. DCSs are also computed using a simple semiclassical optical model. We demonstrate that the restricted NF decomposition provides valuable physical insights into the structured angular distributions of these three chemical reactions. Applications of NF methods to elastic and inelastic molecular angular scattering are also described.

Rigorous quantum dynamical calculations have been performed on the ground 1 1A' and first excited 1 1A" electronic states of the title reaction, employing the most accurate potential energy surfaces available. Product rovibrational quantum state populations and rotational angular momentum alignment parameters are reported, and are compared with new experimental, and quasiclassical trajectory calculated results. The quantum calculations agree quantitatively with experiment, and reveal unequivocally that the 1 1A" excited state participates in the reaction.