Collision-induced dissociation of CS+2. Heat of formation of the CS radical

Abstract

Guided-ion beam mass spectrometry is used to probe the reaction of CS+2 with Xe as a function of ion kinetic energy from thermal to 16 eV. S+, CS+, and Xe+ are the only observed reaction products. Formation of S+(4Su) is observed, even though it is spin forbidden, providing evidence for the importance of spin–orbit coupling in the dissociation of CS+2. The threshold for formation of S++CS, 4.74±0.04 eV, leads to a heat of formation of the CS radical ΔfH00(CS) of 65.8±0.9 kcal/mol. From this value, we derive the bond energies D00(CS)=169.8±0.9 kcal/mol, D00(S–CS)=103.8±0.9 kcal/mol, and D00(O–CS)=158.7±0.9 kcal/mol. The onset for production of CS+ by collision-induced dissociation of CS+2 is observed at 6.16±0.07, 0.40 eV above the thermodynamic threshold, but coincident with the threshold for excitation to the C̃ state of CS+2. The cross section for charge transfer to form Xe+ displays a threshold of ≊2 eV, corresponding to the difference in ionization energies of Xe and CS2. This process is significantly enhanced at higher energies where the concomitant dissociation of CS2 to CS and S becomes accessible.