Collision excitation of sodium cyanide molecule by helium at low temperature

Abstract

Cyanides/isocyanides are the most common metal-containing molecules in interstellar medium. In this work, quantum scattering calculations were carried out to determine the rotational (de-)excitation cross-sections of the most stable form of the sodium cyanide molecule, t-NaCN, in collision with the helium atom. Rate coefficients for the first 43 rotational levels (up to ${j_{{K_a}{K_c}}}$ = 63,3) of NaCN were determined for kinetic temperatures ranging from 1 to 30 K. Prior to that, we constructed a new three-dimensional potential energy surface (3D-PES) for the t-NaCN–He interacting system. These electronic structure computations are done at the CCSD(T)-F12/aug-cc-pVTZ level of theory. Computations show the dominance of Δj = ΔKc = −1 transitions, which is related to the dissymmetric shape of the t-NaCN–He 3D-PES. The NaCN–He rate coefficients are of the same order of magnitude (∼10−11 cm3.s−1) as those of other metal CN-containing molecules such as MgCN and AlCN in collision with He. This work is a contribution for understanding and modelling the abundances and chemistry of nitriles in astrophysical media.

Matrix-Formation Dynamics Dictate Methyl Nitrite Conformer Abundance

“…We propose that the smaller van der Waals radius of the cis conformer enables enhanced trapping over the larger trans conformer, resulting in increased cis abundance in the matrices. However, we acknowledge that we cannot explicitly rule out that this initial enhancement of cis-CH3ONO occurs during the gas-phase portion of the deposition process, since our effusive source is much further from the cold substrate (~8 cm) than previous studies (assumed to be on the millimeter to centimeter scale based on schematics), allowing for more collisions and/or other processes that could enhance the lowest energy conformer, [102][103][104][105][106][107] although we believe it unlikely given the high isomerization barrier of this system.…”

Collision excitation of c-C3H−(X1A1) by He

“…Therefore, clear agreement with Langevin's model is obtained for other anionic systems in collision with H 2 , such as for C 4 H − , 60 C 6 H − , 59 CN − , 83 and C 2 H − with He. 57 It is worth noting that for many similar colliding systems previously studied, such as asymmetric molecules HNS, 84 HSN, 85 and NaCN 86 in collision with He, the de-excitation rate coefficients increase with the initial rotation level j and decrease continuously with increasing |Δj| whatever the temperature range. Preference rules in favor of odd or even Δj have been reported for the systems depending on the shape of the interaction potential.…”