Rotationally resolved vacuum ultraviolet pulsed field ionization-photoelectron vibrational bands for H2+ (X2Σg+, υ+=0-18)

We have obtained a rotationally resolved vacuum ultraviolet pulsed field ionization-photoelectron (VUV-PFI-PE) spectrum of H-2 in the energy range of 15.30-18.09 eV, covering the ionization transitions H-2(+)(X-2 Sigma(+)(g) g upsilon(+)=0-18, N+=0-5)<- H-2(X-1 Sigma(+)(g), upsilon ''=0, J ''=0-4). The assignment of the rotational transitions resolved in the VUV-PFI-PE vibrational bands for H-2(+)(X-2 Sigma(+)(g), upsilon(+)=0-18) and their simulation using the Buckingham-Orr-Sichel (BOS) model are presented. Only the Delta N=N+-J"=0 and +/- 2 rotational branches are observed in the VUV-PFI-PE spectrum of H-2. However, the vibrational band is increasingly dominated by the Delta N=0 rotational branch as upsilon(+) 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 upsilon(+)>= 6 and decreases as upsilon(+) is increased. Thus, the rotationally resolved PFI-PE bands for H-2(+)(upsilon(+)>= 6) presented here provide reliable estimates of state-to-state cross sections for direct photoionization of H-2, while the rotationally resolved PFI-PE bands for H-2(+) (upsilon(+)<= 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 H-2. the ionization energies for the formation of H-2(+) (X-2 Sigma(+)(g), upsilon(+) = 0-18, N+ =0-5) from H-2(+) (X-1 Sigma(+)(g), upsilon ''=0, g, 9 J ''=0-4), the vibrational constants (w(e); w(e)chi(e), w(e)y(e) and w(e)z(e)), the rotational constants (B-upsilon+, D-upsilon+, B-e, and alpha(e)), and the vibrational energy spacings Delta G(upsilon(+)+1/2) for H-2(+)(X-2 Sigma(+)(g), upsilon(+)=0-18) are determined. With 9 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 H-2(+)(X-2 Sigma(+)(g), upsilon(+)=0-18) derived from this VUV-PFI-PE study are in excellent 9 agreement with high-level theoretical predictions.