Rotationally Resolved Vacuum Ultraviolet Pulsed Field lonization-Photoelectron Vibrational Bands for H_2~+(X~2∑_g~+,v~+=0-18)

摘要

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 H_2~+(X~2∑_g~+,v~+=0-18,N~+=0-5)<- H2(X~1∑_g~+,v"=0',J"=0-4).The assignment of the rotational transitions resolved in the VUV-PFI-PE vibrational bands for H_2~+(X~1∑_g~+,v~+=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 H2.However,the vibrational band is increasingly dominated by the DELTA 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 H_2~+(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 H_2~+(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 H_2~+(X~1∑_g~+,v~+=0-18,N~+=0-5)from H_2~+(X~1∑_g~+,v"=0,J"=0-4),the vibrational constants(w_e,w_ex_e,w_ey_e,and w_ez_e),the rotational constants(B_(v~+),D_(v~+),B_e,and alpha_e),and the vibrational energy spacings DELTA G(v~++1/2)for H_2~+(X~1∑_g~+,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 H_2~+(X~1∑_g~+,v~+=0-18)derived from this VUV-PFI-PE study are in excellent agreement with high-level theoretical predictions.