Radiative Association of Atomic and Ionic Carbon

Abstract

We present calculated cross sections and rate coefficients for the formation of the dicarbon cation (C + 2 ) by the radiative association process in collisions of a C( 3 P ) atom and a C + ( 2 P o ) ion. Molecular structure calculations for a number of low-lying doublet and quartet states of C + 2 are used to obtain the potential energy surfaces and transition dipole moments coupling the states of interest, substantially increasing the available molecular data for C + 2 . Using a quantum-mechanical method, we explore a number of allowed transitions and determine those contributing to the radiative association process. The calculations extend the available data for this process down to the temperature of 100 K, where the rate coefficient is found to be about 2 × 10 −18 cm 3 /s. We provide analytical fits suitable for incorporation into astrochemical reaction databases. 1 We remark, somewhat tangentially, that there are also listed 5 polyatomic species, not including, for example, a recent calculation for the sodium ion and the hydrogen molecule (Burdakova et al. 2019).

Polyatomic radiative association by quasiclassical trajectory calculations: Cross section for the formation of HCN molecules in H + CN collisions

“…for the initial quantum state resolved cross section for the collision of two arbitrary molecules, where P (i) r has to be calculated from Eq. (10) or Eq. (11) for the ith trajectory.…”

“…Such ambiguity may introduce discontinuity into the dipole in the LAB frame that is supposed to be used in Eqs. (10)(11). A similar problem appears in reactive dynamics calculation, owing to the sign-ambiguity of the rotation matrix, when the Eckart transformation is utilized to project out the rotational modes 63 .…”

“…Inserting Eqs. (10) and (11) into Eq. ( 2) and integrating over the phase variables (η, χ, ψ), we obtain the initial quantum state resolved semiclassical radiative association cross section for general and neutral polyatomic systems as…”

“…There is another numerical issue regarding the very long trajectories at low collision energies which makes impossible the evaluation of P r in Eq. (10)(11). Based on the Nyquist condition, the maximum frequency that can be represented by Fourier transformation is ω top ∝ n FFT /t traj , where n FFT is the number of sampling points and t traj is the integration time of the trajectory.…”

Chemical promenades: Exploring potential‐energy surfaces with immersive virtual reality

“…An important reaction in this class of systems is that of a carbon atom with the methylidyne cation (among the first discovered molecules in the diffuse interstellar medium, see also Ref. ), leading to formation of a carbon–carbon bond in , a molecule that was detected by mass‐spectroscopic sampling in comets Halley and Giacobini–Zinner and which plays a role in ion‐molecule reactions leading to production of hydrocarbons in interstellar clouds …”