Study on Formation of Interstellar CH from Reactions C + CH and CH + CH.

We interrogated CH produced from reactions C + CH/CH + CH → CH + H using both translational and photoionization spectroscopy. Reactants CH, CH, C, and CH were synthesized in two crossed beams of 1% CH/He ignited by pulsed high-voltage discharge. The individual contributions of reactions C + CH and CH + CH to product CH were evaluated as 17:83 from reactant concentrations in both molecular beams. The translational energy distribution, the angular distribution, and the photoionization efficiency curve of product CH were unraveled. CH was identified as the most stable linear isomer by its photoionization efficiency curve that features two ionization thresholds corresponding to separate transitions to singlet and triplet states of l-CH. The quantum-chemical calculations indicate that the associations of C with CH and CH with CH incur no entrance barriers, and the most favorable exit channel leads to product l-CH + H. It is the first time demonstrating that CH is producible from reactions C + CH and CH + CH on the lowest-lying singlet and triplet potential energy surfaces of CH. This work implies that the reactions of C + CH and CH + CH might have contributions to interstellar CH to some extent as compared with the C + CH reaction commonly adopted in an astrochemical model.