Photoelectron Spectroscopy of the Thiazate (NSO–) and Thionitrite (SNO–) Isomer Anions

Anion photoelectron spectra of the thiazate (NSO‾) and thionitrite (SNO‾) isomers are reported. The NSO‾ photoelectron spectrum showed several well-resolved vibronic transitions from the anion to the NSO radical neutral. The electron affinity of NSO was determined to be 3.113(1) eV. The fundamental vibrational frequencies of NSO were measured and unambiguously assigned to be 1202(6) cm‾¹ (ν₁, asymmetric stretch), 1010(10) cm‾¹ (ν₂, symmetric stretch), and 300(7) cm‾¹ (ν₃, bend). From the presence of vibrational hot band transitions, the fundamental vibrational frequencies of the NSO‾ anion were also measured: 1280(30) cm‾¹ (ν₁, asymmetric stretch), 990(20) cm‾¹ (ν₂, symmetric stretch), and 480(10) cm‾¹ (ν₃, bend). Combined with the previously measured ΔacidH⁰₂₉₈ K(HNSO), D₀(H‾NSO) was found to be 102(5) kcal/mol. Unlike the results from NSO‾, the SNO‾ photoelectron spectrum was broad with little structure, indicative of a large geometry change between the anion and neutral radical. In addition to the spectrally congested spectrum, there was evidence of a competition between photodetachment from SNO‾ and SNO‾ photodissociation to form S‾ + NO. Quantum chemical calculations were used to aid in the interpretation of the experimental data and agree well with the observed photoelectron spectra, particularly for the NSO‾ isomer.