Theory of collision-induced translation-rotation spectra: H2-He

This is the published version, also available here: http://dx.doi.org/10.1103/PhysRevA.29.595.An adiabatic quantal theory of spectral line shapes in collision-induced absorption and emission is presented which incorporates the induced translation-rotation and translation-vibration spectra. The generalization to account for the anisotropy of the scattering potential is given. Calculations are carried out of the collision-induced absorption spectra of He in collisions with H2 with ab initio electric dipole functions and realistic potentials. The anisotropy of the interaction potential is small and is not included in the calculations. The predicted spectra are in satisfactory agreement with experimental data though some deviations occur which may be significant. The rotational line shapes have exponential wings and are not Lorentzian. The connection between the quantal and classical theories is written out explicitly for the isotropic overlap induction

New H2 collision-induced absorption and NH3 opacity and the spectra of the coolest brown dwarfs

We present new cloudy and cloudless model atmospheres for brown dwarfs using recent ab initio calculations of the line list of ammonia (NH3) and of the collision-induced absorption of molecular hydrogen (H2). We compare the new synthetic spectra with models based on an earlier description of the H2 and NH3 opacities. We find a significant improvement in fitting the nearly complete spectral energy distribution of the T7p dwarf Gliese 570D and in near infrared color-magnitude diagrams of field brown dwarfs. We apply these new models to the identification of NH3 absorption in the H band peak of very late T dwarfs and the new Y dwarfs and discuss the observed trend in the NH3-H spectral index. The new NH3 line list also allows a detailed study of the medium resolution spectrum of the T9/T10 dwarf UGPS J072227.51-054031.2 where we identify several specific features caused by NH3.Comment: 37 pages, 13 figures. Accepted for publication in the Astrophysical

Is Sonoluminescence due to Collision-Induced Emission?

We estimate the collision-induced emission (CIE) intensity and profile in the visible and near UV region of the spectrum of N2-X pairs, where X represents another N2molecule or an argon atom, etc. of shock waves believed to exist in sonoluminescence experiments. Calculated profiles consist of superimposed high overtone bands and resemble the measured profiles. Intensities calculated on the basis of a few, simple assumptions concerning the induced dipole surface compare favorably with measurements. The agreement obtained suggests that CIE is an attractive alternative to bremsstrahlung to explain sonoluminescence. The CIE source is optically thin, and the spectral emission profile is not related to Planck's law.University of TexasApplied Research Laboratorie

A new computation of the infrared absorption by H \u3c inf\u3e 2 pairs in the fundamental band at temperatures from 600 to 5000 K

A new computation of the absorption spectrum of H2 pairs in the fundamental band is given for temperatures from 600 to 5000 K. It is based on advanced interaction potentials and recent induced dipole components which were shown to be consistent with the existing laboratory measurements of low-temperature absorption spectra. The absorption is greater by factors of 2-3 than previous estimates and show a different band profile at the higher temperatures

Collision-induced first overtone band of gaseous hydrogen from first principles

In previous work [Phys. Rev. A 40, 6931 (1989)] the interaction-induced dipole moments of H2 pairs have been obtained by treating the complex of the two molecules like one molecule in the self-consistent-field and size-consistent, coupled-electron pair approximations; from this dipole surface, the binary collision-induced absorption spectra have also been computed for the rototranslational and the fundamental band. In the present work, the radial transition matrix elements of the induced dipole components are obtained for the first overtone band of H2 at 1.2 m. Two cases are here considered: v1=00, v2=02 (single vibrational transition) and v1=0-\u3e 1, v2=01 (double transition), where the vi are the vibrational quantum numbers of two interacting H2 molecules (i=1 or 2). The dependence of these dipole elements on the most important initial and final rotational states (j=0,..., 3) is also evaluated. From these results, the spectral profiles of the collision-induced absorption of molecular hydrogen pairs in the infrared 1.2-m (the first H2 overtone) band are obtained. The calculations are based on a proven isotropic potential model which we have extended to account for the effects of vibrational excitations. The comparison of the computated spectra with the measurements available at temperatures from 24 to 300 K shows agreement within the estimated uncertainties of the best measurements (10%). This fact suggests that theory is capable of predicting these spectra reliably at temperatures for which no measurements exist, with an accuracy that compares favorably with that of good laboratory measurements. © 1993 The American Physical Society