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A theoretical study on the rotational dynamics of H2 molecules trapped in the interstitial channels (ICs) of a carbon nanotube bundle is presented. The potential used in this study is modeled as a sum of atom-atom (C-H) van der Waals interactions and electrostatic interactions of the molecule with the surrounding nanotubes.The rotational energy spectra is calculated using a product wave function, where the coupling between translational and rotational modes is treated in a mean-field manner . Molecular dynamics (MD) simulation study was performed for estimating the hydrogen rotational barrier. Both theoretical calculations and simulation results reveal the existence of a large rotational barrier (~ 40 meV). The consequences of this rotational barrier for the rotational energy levels are worked out in detail., Comment: 21 pages, 3 figures, 1 table, accepted for publication in the Journal of Chemical Physics

The resolvent operator formalism of Kolb, Griem (1964), and Baranger (1962) is used to determine the widths and shifts of the fundamental band vibration-rotation lines of HCl under N2 pressure. Time-development operator matrix elements are evaluated accounting for all bilinear and second order anisotropic terms, in addition to isotropic effects to all orders. The method employs the use of a parabolic trajectory model and explicit velocity averaging. The major contributions to the linewidths are found to arise from dipole-quadrupole, quadrupole-quadrupole, and vibrationally dependent isotropic dispersion forces. Good overall agreement is found between calculated and measured widths and linewidths over a 163-295 K temperature range.

The only atomic or molecular spectra known to exhibit 'collisional interference' effects are those of H2 and its isotopes. Attention is presently given to the sharp absorption spectra of HD, which demonstrate collisional interference effects is a fashion that while surprising has been experimentally verified and theoretically characterized in detail. Collisional interference can dramatically alter the line shapes usually encountered in dipole absorption spectra, while nevertheless remaining narrow.

A general theory of atomic dipole coherence under the influence of collisional phase changes, inelastic effects and optically active atom velocity changes, including those due to anisotropic interactions is presented. Velocity change effects are obtained in closed form. Line shapes appear as convolutions of standard pressure broadening contours with velocity-change contours. Width and shift parameters for the He-broadened Na D lines at 2 m bar pressure, 380 K are calculated, as are He-induced photon echo decay rates for these lines. Overall agreement with xperiment is reasonably good.

The collision induced spectra of HD and H2 are studied. Their application to the study of planetary (and planetary satellite) atmospheres is investigated.