We have obtained a rotationally resolved vacuum ultraviolet pulsed
field ionization-photoelectron (VUV-PFI-PE) spectrum of H2 in the
energy range of 15.30-18.09 eV, covering the ionization transitions
H2+(X2Σg+, v+=0-18,
N+=0-5)←H2(X1Σg+, v''=0,
J''=0-4). The assignment of the rotational transitions resolved in
the VUV-PFI-PE vibrational bands for
H2+(X2Σg+, v+=0-18) and their
simulation using the Buckingham-Orr-Sichel (BOS) model are
presented. Only the ΔN=N+ - J''=0 and ±2
rotational branches are observed in the VUV-PFI-PE spectrum of
H2. However, the vibrational band is increasingly dominated by
the △N=0 rotational branch as v+ is increased.
The BOS simulation reveals that the perturbation of VUV-PFI-PE
rotational line intensities by near-resonance autoionizing Rydberg
states is minor at v+ ⩾6 and decreases as v+ is increased.
Thus, the rotationally resolved PFI-PE bands for
H2+(v+ ⩾6) presented here provide reliable estimates
of state-to-state cross sections for direct photoionization of
H2, while the rotationally resolved PFI-PE bands for
H2+(v+ ⩽5) are useful data for fundamental
understanding of the near resonance autoionizing mechanism. On the
basis of the rovibrational assignment of the VUV-PFI-PE spectrum of
H2, the ionization energies for the formation of
H2+(X2Σg+, v+=0-18, N+=0-5) from
H2+(X1Σg+, v''=0, J''=0-4), the
vibrational constants (ωe, ωeχe, ωeye,
and ωeze), the rotational constants (Bv+, Dv+,
Be, and αe), and the vibrational energy spacings ΔG(v++1/2) for H2+(X2Σg+, v+=0-18)
are determined. With a significantly higher photoelectron energy
resolution achieved in the present study, the precisions of these
spectroscopic values are higher than those obtained in the previous
photoelectron studies. As expected, the spectroscopic results for
H2+(X2Σg+, v+=0-18) derived from this
VUV-PFI-PE study are in excellent agreement with high-level
theoretical predictions.