An extension of the classical trajectory approach is proposed that may be useful in treating many types of nonadiabatic molecular collisions. Nuclei are assumed to move classically on a single potential energy surface until an avoided surface crossing or other region of large nonadiabatic coupling is reached. At such points the trajectory is split into two branches, each of which follows a different potential surface. The validity of this model as applied to the HD2+ system is assessed by numerical integration of the appropriate semiclassical equations. A 3d “trajectory surface hopping” treatment of the reaction of H+ with D2 at a collision energy of 4 eV is reported. The excellent agreement with experiment is an encouraging indication of the potential usefulness of this approach.
Approximate potential-energy surfaces for the two lowest singlet states of H3+ are calculated using the diatomics-in-molecules approach. The nonadiabatic terms which couple these surfaces can be directly computed in this approximation. From the magnitudes of these coupling terms it is apparent that, for excitation energies below about 10 eV, nonadiabatic transitions must be confined almost entirely to a region localized at the avoided crossing of the two surfaces. This fact suggests the following simplified picture of the dynamics of the H++H2 reaction: As the H+ and H2 approach, they remain on the lower potential surface (there is no initial electron jump). They continue to follow adiabatically the lower surface in the close-collision region, so the probability of a nonadiabatic transition does not appear to be related to the lifetime of the collision complex. It is while the products are receding that electronic transitions become important. Consequences of this model on the threshold for formation of H2+ and on the partition of vibrational energy in the products are discussed, and a comparison with recent experiments of Krenos and Wolfgang is included.
It is maintained that quenching of O(1D) by collision with N2 proceeds by formation of a collision complex on the lowest singlet potential surface. Once a collision complex is formed, even the weak spin−orbit interaction in O atom can induce quenching with essentially unit probability (at thermal energies) because the intersection of the singlet [O(1D) + N2] and triplet [O(3P) + N2] potential surfaces is crossed many times during the life of the complex. Rather crude, but qualitatively reasonable potential surfaces for O(1D) + N2 are constructed and classical trajectory calculations carried out to show that the cross section for complex formation is indeed appreciable, ∼40 Å2 at thermal energy; a statistical model is used to determine the quenching probability of the collision complex. Values obtained for the magnitude of the thermal rate constant for quenching, and the fraction of the exoergicity which appears as vibrational excitation of N2, are both in good agreement with experimental results.
With a data sample containing 1.1 x lo5 J/$ -+ /L+/L-decays reconstructed with 16 M~V / C ' rms mass resolution, we have measured the differential cross sections versus Feynman-x, rapidity, and p~ for the production of J/$ and 4' in 800 GeVlc p A u collisions. Our results are compared with leading-order QCD predictions and with previous measurements. While the shapes of the cross sections are in qualitative agreement with QCD predictions, the magnitudes disagree by factors of 7 ( J / 4 ) and 25 (4'). Assuming an appropriate form for the differential cross sections in regions not measured, we derive a total J/+ production cross section a ( p + N + J/$ + X) = 442 f 2 i 88 nb/nucleon and a (model-dependent) total 4' cross section u(p + N + $' + X) = 75 f 5 f 22 nblnucleon. For J/$ produced at central rapidity, du(p + N + J/$ + X)/dyly=o = 230 i 5 f 46 nb/nucleon. PACS number(s): 13.85. Ni, 24.85.+p, 25.40.Ve
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