[en] A great variety of experimental techniques now makes it possible to obtain dynamical information on single bimolecular collisions in a very direct way. These methods are too numerous to permit a comprehensive review in this article, but a few examples have been chosen to illustrate briefly the types of results being obtained in several areas. These include measurements of state-to-state differential cross sections for rotationally and vibrationally inelastic collisions, and rearrangement collisions studies by crossed-beam and merged-beam methods. (orig.)

No abstract available

[en] Collision rates of some excited-state processes can be studied at low effective temperatures with a single atomic or molecular beam. Effects dependent on the orientation of the collision axis can also be observed in resonant collisions. Useful relative-velocity distributions are given. (author)

[en] A new empirical (rigid rotor) fit potential of the H₂-H₂ system has been determined for reporducing measured quantities which are especially senstive to the full non-spherical interaction in the attractive region. The leading potential terms have been adapted one after the other: the isotropic term V₀₀₀ has been probed by comparing with measured second virial coefficients^1,2, at temperatures up to 200 K, the anisotropic term V₀₂₂(=V₂₀₂) has been adapted to reproduce measured hyperfine spectra of ortho-H₂-para-H₂ dimers observed in a molecular beam magnetic resonance apparatus³, and the corresponding data observed for the ortho-H₂-ortho-H₂ dimers have been used to adapt the quadrupole-quadrupole interaction term V₂₂₄ as well. Satisfying quantitative agreement has been achieved in all these fits

[en] The phenomenon of molecular chattering (a collision between two rigid ovaloids involving two or more impulsive hits) is investigated with emphasis on the importance of these collisions on kinetic theory calculations for dilute molecular systems. To facilitate this analysis, the pseudo-Liouville formalism, commonly employed in the kinetic theory of rigid spheres, is generalized to a form appropriate to rigid ovaloids. From this formalism, we derive a chattering expansion of the bracket integrals, the terms of which successively incorporate higher order chattering sequences. Finally, the results of scattering trajectories between a rigid sphere and a rigid ellipsoid are reported. It is demonstrated that the neglect of chattering sequences leads to large errors when calculating the bracket integrals for realistic model parameters; the errors ranging from approx.1% to as high as approx.200%

[en] The study of collision induced (CI) light scattering spectra of atomic or molecular gases provides a test for the polarizability invariants of interacting molecular pairs. For an isolated molecule of point group symmetry Tsub(d), the permanent polarizability is isotropic. Due to interaction with neighbouring molecules the effective polarizability contains fluctuating anisotropic polarizability contributions of 2sup(nd) tensorial rank, which give rise to depolarised CI scattering. In this work light scattering from carbon tetrachloride vapour (in coexistence with the respective liquid) was observed on an absolute scale. The calibration was performed by an external procedure using the rotational Raman spectra of nitrogen gas as a standard. Furthermore, a theoretical calculation of the binary interaction induced spectrum was performed, which is based a) on a point multipole expansion of the interaction induced polarizability b) on a classical free trajectory model for the translational pair motion c) on free rotational wave functions. Without use of adjustable parameters agreement with the experiment is achieved in the wavenumber range of 10 cm^-1 to 25 cm^-sup1 relative to the exiting Laser at 19436.5 cm^-1, proving the predominance of the dipole-induced-dipole (DID) effect. Deviations at smaller wavenumber shifts may be explained by the existence of bound dimers. Experimental intensities in excess of the DID-effect for wavenumber shifts larger than 25 cm^-1 point to the contribution of additional mechanisms, i.e. the CI-rotational Raman (CIRR) transitions. To lowest order, the CIRR effect invokes the dipole-quadrupole polarizability A and the dipole-octopole polarizability E. Estimates for A and E have been obtained from a fit of the theoretical spectrum to the experimental data. (Author)

[en] Collision induced dissociation in mass spectrometry of protonated nucleosides typically yields as charged fragment the protonated nucleo-base augmented by one hydrogen transferred from the 2'-deoxyribose, [bH₂]. The origin of the hydrogen transfer for the protonated 2'-deoxyguanosine has been investigated by collision induced dissociation of deuterium enriched molecules. [1'-²H]2'-deoxyguanosine, [2',2''-²H₂]2'-deoxyguanosine, and [5',5''-²H₂]2'-deoxyguanosine have been studied and deuterium/hydrogen back exchange has been used following complete or partial exchange of the 2'-deoxyguanosine in solution. Based on the fragmentation of the deuterated molecular ions, the hydrogen transferred from the 2'-deoxyribose to the guanine is found to originate from the O5' atom on the 2'-deoxyribose. A fragmentation mechanism involving a hydrogen shift from the 2' position to the oxygen atom O5' and supported by the kinetic isotope effect on the survival yield curves is proposed. The influence of the 2'-deoxyguanosine conformation on the hydrogen transfer and the fragmentation mechanism is discussed. (authors)

[en] Classical functional sensitivity analysis has been used to probe the detailed physics of how the dynamics is coplanar rotationally inelastic collisions of H₂ and HD draws on the underlying potential energy surface. A new expression for the full sensitivity map is derived, and maps are calculated as a function of angle for the three observables of interest at two values of the initial relative kinetic energy. These full sensitivity maps were compared with full sensitivity maps generated from a truncated Fourier sum. This comparison showed that a Fourier sum of radial sensitivity coefficients (δO/δv_m1,m2) through m₁, m₂ = ±6 was sufficient to generate full sensitivity maps. The effect of varying the initial relative kinetic energy was found to have a profound effect on both the radial sensitivity coefficients and the full sensitivity maps and indicates that a localized perturbation of the potential will affect observables differently at different values of the initial relative kinetic energy. 36 refs., 11 figs., 2 tabs

[en] Collision-induced changes in the space-fixed body-frame angular momentum projection, M, occur in all systems, within limits imposed by the isotropy of the collision environment. Their significant effect on the relationship between calculated inelastic rates and observed linewidths and state-to-state rates is often neglected. Because of the properties of the multipole, or tensor opacity, expansion of the relaxation matrix, M-memory on collision is expected to be greatest for low-order multipole interactions, as in the case of H₂CO. The lowest order permanent multipole in CH₄ is the octopole. Surprisingly, CH₄ ground state collisions in the E manifold (where several levels are missing due to nuclear spin statistics) show strong M-memory in low J levels, both in 3 level DR, and in 4 level DR to adjacent levels. The authors analysis of M-changing collisions uses the statistical tensor reduction of the equations for the time-evolution rates expanded in an extended ECS/tensor opacity form to identify the simplest model consistent with the observed polarization dependence of the 3 and 4 level double resonance signals

[en] A new version of Johnson's log derivative method for integrating the (nonreactive) Schrodinger equation is described. The new feature is that the log derivative equation is integrated inward (from large r to small r) with initial conditions that correspond to asymptotically incoming (or outgoing) radial waves. The result is that the log derivative function Q(r) (which is now a complex function of r) is a very smooth, nonsingular function (compared to the oscillatory, singular behavior of Q(r) with the usual real boundary conditions), meaning that many fewer grid points are required for its numerical integration. The number of grid points necessary to achieve a given level of accuracy is also only a weak function of the scattering energy E or the mass of the particles. Test calculations for a one-dimensional and a multichannel example illustrate this behavior