Crossed molecular beam: I. Photoionization studies of hydrogen sulfide and its dimer and trimer. II. A rotating source crossed molecular beam apparatus

Photoionization efficiency data fof H2S+, S+ and HS+ have been obtained in the region 645 to 1190 A using the molecular beam method. The ionization energy of H2S was determined to be 10.4607 +- 0.0026 eV (1185.25 +- 0.30 A). The observed autoionizing vibrational progressions are tentatively assigned to the Rydberg transitions: 5a1 → nsa1 (n = 5 and 6) and 2b2 → nda1 (n = 4 and 5). The internal energy effects and the energetics of the ion-molecule reactions H2S+ + H2S → S2+ +2H2, HS2+ + H2 + H, H3S+ + HS, and H3S2+ + H have been studied by photoionization of hydrogen sulfide dimers which were synthesized by the molecular beam method. The appearance energy (AE) for H3S+ from (H2S)2 was determined to be 10.249 +- 0.012 eV (1209.7 +- 1.5 A). This value allows the calculation of the absolute proton affinity for H2S at 0 K to be 167.2 +- 1.4 kcal/mol. Using the measured ionization energies for (H2S)2+ (9.596 +- 0.022 eV) and (H2S)3+ (0.467 +- 0.022 eV) and the estimated bonding energies for H2S.H2S and (H2S)2.H2S(0.05 eV), the bond dissociation energies for H2S+.H2S and (H2S)2+.H2S are deduced to be 0.92 +- 0.04 and 0.18 +- 0.04 eV. The AE for H3S+.H2S from (H2S)3 (9.84 +- 0.04 eV) also makes possible the calculation of the bond dissociation energy for H3 H3S+.H2S to be 0.46 +- 0.10 eV. An experimental apparatus is described for crossed neutral-neutral molecular beam studies; a rotating source crossed molecular beam apparatus