Shiell RC, Hu X, Hu QJ, Hepburn JW
Chemistry Department, University of Waterloo, ON, Canada.
Faraday Discuss. 2000(115):331-43; discussion. doi: 10.1039/a909428h.
The threshold ion-pair production spectra at the J" = 0 and J" = 1 thresholds of H2 and J" = 0, 1 and 2 thresholds of D2 obtained with single photon excitation are presented. The ion-pair yield spectra of H2 and D2 over these energy ranges demonstrate strong resonant enhancement, parts of which dominate the TIPPS signals, permitting the assignment of the lower states of these resonances. From those thresholds with weak resonant enhancement (the J" = 0 threshold of H2 and the J" = 1 threshold of D2) a very small direct contribution to ion-pair production can be observed. The behaviour of the TIPPS spectra taken with different applied discrimination fields is understood by modeling the field ionization behaviour of a MATI spectrum of H2, containing both the similarly resonantly enhanced v+ = 8 S(0) ionization threshold and the non-resonantly enhanced S(1) ionization threshold. From the H2 J" = 1 and D2 J" = 0 TIPPS spectra the energetic field-free thresholds of the H2 and D2 ion-pair limits were determined to be 139,714.8 +/- 1.0 cm-1 and 140,370.2 cm-1 +/- 1.0 cm-1, respectively.
给出了通过单光子激发获得的H₂在J" = 0和J" = 1阈值以及D₂在J" = 0、1和2阈值下的阈上离子对产生光谱。H₂和D₂在这些能量范围内的离子对产率光谱显示出强烈的共振增强，其中部分共振增强主导了阈上离子对产生光谱（TIPPS）信号，从而可以确定这些共振的低能态。从那些共振增强较弱的阈值（H₂的J" = 0阈值和D₂的J" = 1阈值）可以观察到对离子对产生的非常小的直接贡献。通过对包含同样共振增强的v+ = 8 S(0)电离阈值和非共振增强的S(1)电离阈值的H₂的多光子电离（MATI）光谱的场电离行为进行建模，理解了在不同应用鉴别场下获得的TIPPS光谱的行为。从H₂的J" = 1和D₂的J" = 0 TIPPS光谱中，确定H₂和D₂离子对极限的无场能量阈值分别为139,714.8 +/- 1.0 cm⁻¹和140,370.2 cm⁻¹ +/- 1.0 cm⁻¹。
