Double resonance spectroscopy of several highly excited rovibronic states of H₂

Abstract

The energies of several highly excited levels of the B1Σ+u, B′1Σ+u and C 1Πu states of molecular hydrogen, located several hundred wave numbers below the second dissociation limit, have been measured using two-colour, resonantly enhanced multi-photon ionization. The states were probed by excitation from the double-well E, F 1Σ+u state, populated by two-photon excitation from the ground state. Ion production was detected as a function of wavelength using a time-of-flight mass spectrometer. Non-adiabatic couplings extensively mix the configurations of the B 1Σ+u, B′1Σ+u and C 1Πu states leading to perturbations that are predicted to vary considerably as a function of rotational and vibrational excitation. Term energies are compared to previous measurements and to ab initio theoretical calculations which include non-adiabatic effects. Several observed discrepancies with the calculations and previously reported energies are discussed. Term energies for two rovibronic levels are reported for the first time.

1Σu and 1Πu states of the hydrogen molecule: Nonadiabatic couplings and vibrational levels

“…This seems to be also true for the C state despite Comparison with experiment, Ref. [14]. a C + , C À denote the C P + , C P À levels, respectively.…”

“…[14], are compared with our present computations in Table 7. The B state results are consistent with Table 5 which shows that for J = 0 our close-coupling term values for higher lying levels of this state are over 2 cm À1 too high and a similar error is to be expected for J > 0.…”

Broadening and intensity redistribution in theNa(3p)hyperfine excitation spectra due to optical pumping in the weak excitation limit

“…Since the experiments were performed at low number densities of sodium atoms (n 3s ∼10 10 cm −3 ), lineshape modifications by radiation trapping can be disregarded [7,8]. We attribute the observed lineshape effects to op-tical pumping, which leads to depletion broadening of spectral lines [9,10]. If transit time τ tr of atoms through the laser beam is much larger than lifetime τ nat of the 3p state, populations of levels and the associated fluorescence signals can become nonlinear on laser intensity I las long before the saturation limit is reached (i.e., at I las ≪ I sat ).…”