The H - NCS bond energy , AHo , ( HNCS ) , AHo , ( NCS ) , and IP ( NCS ) from photoionization mass spectrometric studies of HNCS , NCS , and ( NCS )

The species HNCS and NCS have been studied by photoionization mass spectroscopy. The adiabatic ionization potential (IP) of HNCS is 69.92 eV, the shape of the ion yield.curve near threshold implies a large change in geometry, perhaps to linear HNCS+. Various appearance potentials (AP) from HNCS are determined by a more objective procedure, from which AH>(HNCS)>29.6 kcal/ mol (and very likely >31.0?0.7 kcal/mol) is deduced. The adiabatic IP of NCS is 10.689rtO.005 eV. This quantity, together with AP(NCS+/HNCS), yields D,(H-NCS)G97.2%0.2 kcal/mol. However, a measurement of the appearance potential of NCS+ from (NCS)2 results in a still lower value, D,(H-NCS)G93.3? 1.1 kcal/mol, and AH”f,(NCS) G 72.7 + 0.8 kcal/mol. Approximate values are obtained for AflfO(HNCS+) and for the proton affinity of NCS.