Inelastic cross sections and rate coefficients for collisions between CO and H2

Abstract

A five-dimensional coupled states (5D-CS) approximation is used to compute cross sections and rate coefficients for CO+H 2 collisions. The 5D-CS calculations are benchmarked against accurate six-dimensional close-coupling (6D-CC) calculations for transitions between low-lying rovibrational states. Good agreement between the two formulations is found for collision energies greater than 10 cm −1 . The 5D-CS approximation is then used to compute two separate databases which include highly excited states of CO that are beyond the practical limitations of the 6D-CC method.The first database assumes an internally frozen H 2 molecule and allows rovibrational transitions for v ≤ 5 and j ≤ 30, where v and j are the vibrational and rotational quantum numbers of the initial state of the CO molecule. The second database allows H 2 rotational transitions for initial CO states with v ≤ 5 and j ≤ 10. The two databases are in good agreement with each other for transitions that are common to both basis sets. Together they provide data for astrophysical models which were previously unavailable.

The Leiden Atomic and Molecular Database (LAMDA): Current Status, Recent Updates, and Future Plans

“…This can be extensions to higher rotational levels, addition of hyperfine structure, and extension to vibrational or even electronic transitions. This category includes rovibrational CO-H 2 [122], rovibrational CO-H [123], HCO + -H 2 to 500 K [124], hyperfine N 2 H + -H 2 [125], and rovibrational SiO-He [126].…”

“…Rovibrational CO: Thanks to the efforts of Castro et al [122], there now exists a set of cross sections and rate data for ortho-H 2 and para-H 2 collisions with CO that is complete for vibrational quanta v = 0 − 5 and rotational quanta J ≤ 40. In addition, Li et al [147] have published a careful re-evaluation of vibration-rotation line lists for nine isotopologues of CO. We are preparing a LAMDA-format data file that incorporates all of these molecular data.…”

Machine-learning-corrected quantum dynamics calculations

“…For the CS approximation, l ≡ J is the average value of l between |J − j 12 | and J + j 12 . Details of the potential energy surfaces and scattering calculations for the present collision systems have been reported previously [34][35][36][37][38]. For the internal energy of the molecules, we use…”

Absolute measurements of state-to-state rotational energy transfer between CO and H2 at interstellar temperatures

“…The CO-H 2 collisional system has been investigated theoretically [2][3][4][5][6][7][8][9][10][11][12] and experimentally [8,13,14] in the past. The lowest temperature at which absolute rate coefficients have been measured is 77 K [13].…”