Multireference configuration interaction study of the predissociation of C$_{2}$ via its $F\,^1Π_u$ state

Zhongxing Xu; S. R. Federman; William M. Jackson; Cheuk-Yiu Ng; Lee-Ping Wang; Kyle N. Crabtree

doi:10.1063/5.0097451

paper

Multireference configuration interaction study of the predissociation of C $_{2}$ via its $F^{1} Π_{u}$ state

arXiv:2206.03540 · doi:10.1063/5.0097451

Abstract

Photodissociation is one of the main destruction pathways for dicarbon (C $_{2}$ ) in astronomical environments such as diffuse interstellar clouds, yet the accuracy of modern astrochemical models is limited by a lack of accurate photodissociation cross sections in the vacuum ultraviolet range. C $_{2}$ features a strong predissociative $F^{1} Π_{u} - X^{1} Σ_{g}^{+}$ electronic transition near 130 nm originally measured in 1969; however, no experimental studies of this transition have been carried out since, and theoretical studies of the $F^{1} Π_{u}$ state are limited. In this work, potential energy curves of excited electronic states of C $_{2}$ are calculated with the aim of describing the predissociative nature of the $F^{1} Π_{u}$ state and providing new ab initio photodissociation cross sections for astrochemical applications. Accurate electronic calculations of 56 singlet, triplet, and quintet states are carried out at the DW-SA-CASSCF/MRCI+Q level of theory with a CAS(8,12) active space and the aug-cc-pV5Z basis set augmented with additional diffuse functions. Photodissociation cross sections arising from the vibronic ground state to the $F^{1} Π_{u}$ state are calculated by a coupled-channel model. The total integrated cross section through the $F^{1} Π_{u}$ $v = 0$ and $v = 1$ bands is 1.198 $\times$ 10 $^{- 13}$ cm $^{2}$ cm $^{- 1}$ , giving rise to a photodissociation rate of 5.02 $\times$ 10 $^{- 10}$ s $^{- 1}$ under the standard interstellar radiation field, much larger than the rate in the Leiden photodissociation database. In addition, we report a new $2^{1} Σ_{u}^{+}$ state that should be detectable via a strong $2^{1} Σ_{u}^{+} - X^{1} Σ_{g}^{+}$ band around 116 nm.

33 pages, 13 figures; Accepted by The Journal of Chemical Physics

Multireference configuration interaction study of the predissociation of C2​ via its F1Πu​ state

Abstract

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Multireference configuration interaction study of the predissociation of C $_{2}$ via its $F^{1} Π_{u}$ state