Potential energy surface and rate coefficients of protonated cyanogen (HNCCN+) induced by collision with helium (He) at low temperature

Abstract

Nitriles have been identified in space. Accurately modelling their abundance requires calculations of collisional rate coefficients. These data are obtained by first computing potential energy surfaces (PES) and cross-sections using high accurate quantum methods. In this paper, we report the first interaction potential of the HNCCN + -He collisional system along with downward rate coefficients among the 11 lowest rotational levels of HNCCN + . The PES was calculated using the explicitly correlated coupled cluster approach with simple, second, and non-iterative triple excitation (CCSD(T)-F12) in conjunction with the augmented-correlation consistentpolarized valence triple zeta Gaussian basis set. It presents two local minima of ∼283 and ∼136 cm −1 , the deeper one is located at R = 9 a 0 towards the H end (He• • • HNCCN + ). Using the so-computed PES, we calculated rotational cross-sections of HNCCN + induced by collision with He for energies ranging up to 500 cm −1 with the exact quantum mechanical close coupling method. Downward rate coefficients were then worked out by thermally averaging the cross-sections at low temperature (T ≤ 100 K). The discussion on propensity rules showed that the odd j transitions were favoured. The results obtained in this work may be crucially needed to accurately model the abundance of cyanogen and its protonated form in space.

A new protonated molecule discovered in TMC-1: HCCNCH+

“…We also carried out excitation calculations using the Large Velocity Gradient (LVG) method with a code written by M. Agúndez (see some details in Agúndez 2009), which is similar to other codes such as MADEX (Cernicharo 2012) and RADEX ( Van der Tak et al 2007). We consider inelastic collisions with H 2 and He adopting the rate coefficients calculated for collisions between NCCNH + and He (Bop et al 2018). We adopt an abundance of He of 0.17 relative to H 2 and scale the rate coefficients calculated for He, when applied to H 2 , by multiplying them by the squared ratio of the reduced masses of the H 2 and He colliding systems.…”

Electronic structure calculations and quantum dynamics of rotational deexcitation of CNNC by He

“…In fact, since He has two electrons in a closed shell, it could be a good template for the para -H 2 molecule. 43,44 For instance, the collisional dynamical study of several isocyano molecules such as NCCN, 41 CNCN, 42 NCCNH + , 45 HNC, 46 and SiNC 47 with He as a collider have been discussed, but collisional data of CNNC with He are not available to date.…”

Hyperfine excitation of NS+ due to para-H2(j = 0) impact

“…Such an approximation will significantly reduce the computational efforts. In fact, charged species strongly interact with He (Bop et al 2016(Bop et al , 2017(Bop et al , 2018 and then much more with H 2 leading to very deep potential wells. Such well depths supplemented by the low rotational constant of NS + (∼ 0.83 (Cernicharo et al 2018)) would make the dynamic calculations computationally expensive.…”