THE PHOSPHOROTRITHIOUS ACID (HS)3P IS STABLE IN THE DILUTE GAS PHASE

Using the technique of neutralization-reionization mass spectrometry (NRMS) it could be shown that the elusive phosphorotrithious acid (HS)3P is a stable molecule in the rarefied gas phase. A triple propene elimination from the molecular ions of the dipropyl ester of propylphosphonotrithioic acid, PrP(S)(SPr)2, (70 eV EI) yields m/z 130 radical cations of composition “[H3PS3] +”. Analysis of their collisional activation (CA) mass spectrum using thermochemical data, shows that these “[H3PS3] +” ions have the structure [(HS)3P] + rather than that of the tautomer [(HS)2P(=S)H| +. Subjected to a NRMS experiment, these ions retain their structure and are cleanly reduced to (HS)3P. The results are entirely compatible with ab initio MO-calculations executed at the HF/3-21G* and HF/6-31G** levels of theory (GAUSSIAN 92 system of programs). The calculations predict that [(HS)3P] + and [(HS)2P(=S)H] + and their respective neutral counterparts are local minima which are separated by high potential energy barriers. Neutral (HS)3P is calculated to be lower in energy than its tautomer (HS)2P(=S)H but upon ionization this order of stability is reversed.