The 4fstates of He2: A new spectrum of He2in the near infrared

摘要

A new spectrum of the He2molecule has been discovered in the region 5100ndash;5900 cmminus;1. It is identified as the 4fndash;3dRydberg transition of He2with a weak contribution of 4dndash;3pin the same region. The uncoupling oflfrom the internuclear axis in both the triplet and the singlet system is almost complete in the 4fcomplex; the appropriate quantum number isN+corresponding to the rotational angular momentum of the He+2core. The electronic fine structure in eachN+level depends on the dipole polarizability agr; of the core and its anisotropy as well as on the quadrupole momentQ2and higher momentsQ4,... of the core. Conversely, from the observed structure some of the quantities characterizing the core have been determined, e.g., agr;=1/3(2agr;perp;+agr;par;) =2.82 plusmn;0.02,Q2=1.39plusmn;0.13,Q4=0.99plusmn;0.14, all in atomic units. The detailed rotational analysis of the spectrum shows that widespread perturbations occur in the triplet 4flevels, the largest affecting theN=6,N+=3 andN=9,N+=7 levels which are shifted towards higher energies by 1 and 2 cmminus;1, respectively. The perturbations are clearly caused by Dgr;l=2 interaction with corresponding levels of 4ppgr; for which Orth and Ginter have found the opposite perturbations. There are no similar perturbations in the corresponding singlet levels.