Vacuum ultraviolet pulsed-field ionization-photoelectron study of H_2S in the energy range of 10-17 eV

摘要

Vacuum ultraviolet pulsed-field ionization-photoelectron(PFI-PE)spectra of H_2S have been recorded at PFI-PE resolutions of 0.6-1.0 meV in the energy range of 10-17 eV using high-resolution synchrotron radiation.The PFI-PE spectrum,which covers the formation of the valence electronic states H_2S~+(X~2B_1,A~2A_1,and B~2B_2),is compared to the recent high-resolution He I photoelectron spectra of H2S obtained by Baltzer et al [Chem.Phys.195,403(1995)].In addition to the overwhelmingly dominated origin vibrational band,the PFI-PE spectrum for H_2S~+(X~2B_1) is found to exhibit weak vibrational progressions due to excitation of the combination bands in the v_1~+ symmetric stretching and v_2~+ bending modes.While the ionization energy(IE)for H_2S~+(X~2B_1)obtained here is in accord with values determined in previously laser PFI-PE measurements,the observation of a new PFI-PE band at 12.642(+-)0.001 eV suggests that the IE for H_2S~+(A~2A_1)may be 0.12 eV lower than that reported in the He I study.The simulation of rotational structures resolved in PFI-PE bands shows that the formation of H_2S~+(X~2B_1)and H_2S~+(A~2A_1)from photoionization of H_2S(X ~1A_1) is dominated by type-C and type-5 transitions,respectively.This observation is consistent with predictions of the multichannel quantum defect theory.The small changes in rotational angular momentum observed are consistent with the dominant atomiclike character of the 2b_1 and 5a_1 molecular orbitals of H2S.The PFI-PE measurement has revealed perturbations of the(0,6,0)K~+=3 and (0,6,0)K~+=4 bands of H_2S~+(A~2A_1).Interpreting that these perturbations arise from Renner-Teller interactions at energies close to the common barriers to linearity of the H_2S~+(X~2B,and A ~2A,)states,we have deduced a barrier of 23 209 cm~(-1) for H_2S~+(X~2B_1)and 5668 cm~(-1) for H_2S~+(A ~2A_1).The barrier of 23 209 cm~(-1)for H_2S~+(X ~2B_1)is found to be in excellent agreement with the results of previous studies.The vibrational PFI-PE bands for H_2S~+(B ~2B_2)are broad,indicative of the predissociative nature of this state.