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A theoretical study is reported for the dependence of the E, F 1Σ+g–X 1Σ+g (vE=0, vX) Q-branch two-photon transitions on the initial vibrational and rotational quantum numbers vX and J for H2, HD, and D2. The magnitude of the two-photon transition moment |Mfo| increases with vX between 0 and 2, then decreases rapidly at higher vX. This behavior is ascribed to (constructive and destructive) interference effects in the two-photon transition, which vary with the nodal behavior of the initial-state vibrational wave function. The J dependence of |Mfo| is most strongly affected by the changes in vibrational wave functions caused by centrifugal distortion of the vibrational potentials. At low to intermediate J, the Franck–Condon overlap improves, resulting in a slow, monotonic increase of |Mfo| with J. At higher J, resonant tunneling between the inner and outer wells of the E, F state introduces sharp variations in the |Mfo| structure. Near the top of the barrier, nonresonant tunneling in the E-state vibrational wave function causes a general decrease in |Mfo| with J. [ABSTRACT FROM AUTHOR]

The relationship between quantum-state populations and ion signals in (2+1) resonance-enhanced multiphoton ionization (REMPI) detection of H2, HD, and D2 via the E, F 1Σ+g (v’E=0, J’=J‘)–X 1Σ+g (v‘,J‘) transition is determined by calibration against a thermal effusive source. Correction factors are obtained for 102 rovibrational levels for v‘=0, 1, and 2 and J‘ ranging from 0 to 17. Within a given v‘, rotational correction factors are nearly unity except for the highest J‘ levels. The vibrational correction factors vary with v‘; (2+1) REMPI detection is 2–3 times more sensitive to v‘=1 and 2 than to v‘=0. Experimental correction factors are compared with those derived from a theoretical calculation of the two-photon transition moments by Huo et al. [J. Chem. Phys. 95, xxxx (1991)]. In general, the agreement is excellent, which suggests that theoretical correction factors may be used when experimental ones are unavailable. [ABSTRACT FROM AUTHOR]

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