ABSTRACT Rate coefficients for rotational transitions in HD induced by H2 impact for rotational levels of HD j ≤ 8 and temperatures 10 K ≤ T ≤ 5000 K are reported. The quantum mechanical close-coupling (CC) method and the coupled-states (CS) decoupling approximation are used to obtain the cross-sections employing the most recent highly accurate H2–H2 potential energy surface (PES). Our results are in good agreement with previous calculations for low-lying rotational transitions The cooling efficiency of HD compared with H2 and astrophysical applications are briefly discussed.
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Rotational excitation of methanol in collisions with molecular hydrogen
This paper presents rate coefficients for transitions between rotational levels of the A-type and E-type nuclear spin modifications of methanol induced by collisions with molecular hydrogen. These rate coefficients are required for an accurate determination of methanol abundance in the interstellar medium, where local thermodynamic equilibrium conditions generally do not apply. Time-independent close-coupling quantum scattering calculations have been employed to calculate cross-sections and rate coefficients for the (de-)excitation of methanol in collisions with para- and ortho-H2. These calculations utilized a potential energy surface (PES) for the interaction of methanol with H2 recently computed by the explicitly correlated CCSD(T)-F12a coupled-cluster method that employed a correlation-consistent aug-cc-pVTZ basis. Rate coefficients for temperatures ranging from 3 to 250 K were calculated for all transitions among the first 76 rotational levels of both A-type and E-type methanol, whose energies are less than or equal to 170 K. These rate coefficients are compared with those by Rabli and Flower who carried out coupled-state calculations using a PES computed by second-order many-body perturbation theory. Simple radiative transfer calculations using the present set of rate coefficients are also reported and compared with such calculations using the rate coefficients previously computed by Rabli and Flower.
more » « less- NSF-PAR ID:
- 10473840
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 527
- Issue:
- 2
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 2209-2213
- Size(s):
- ["p. 2209-2213"]
- Sponsoring Org:
- National Science Foundation
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