Photoionization of jet-cooled HI with coherent vacuum ultraviolet radiation: Evidence for Hund’s case (e)

Abstract

In the range of 83 500-89 200 cm -', the photoionization spectrum of HI is strongly influenced by autoionization of Rydberg series converging to the higher lying 2B,,2 component of the spin-orbit split 'H ionic ground state. The photoelectron yield spectrum, exhibiting the various autoionization processes, has been measured on a rotationally cooled sample ( T,,, -13 K), with a spectral resolution of the exciting vacuum ultraviolet radiation of 0.5 cm -'. Using a multichannel quantum-defect theory treatment explicitly including rotation, we calculate spinorbit and rotational autoionization fine structure in the spectrum. In order to find a qualitative agreement of theory and experiment, the Rydberg states of HI have to be described in terms of a transition in angular momentum coupling cases, going from Hund's case (c) to case (e).

Angle- and spin-resolved photoelectron spectroscopy in rotationally resolved photoionization of HI

“…The expansion of 150 mbar neat HI through a 300 lxm orifice leads to a rotational temperature of approx. 13 K. This value can be deduced from the rotational structure observed in the photoionization spectrum [11,16] and from results of 1 + 1 REMPI via the b 3I/1 state [22].…”

“…This theory was then applied to a calculation using pure Hund's case (e) coupling and compared with available experimental cross section and spin polarization results [21]. Lefebvre-Brion has then extended the calculations to include a transition in angular momentum coupling from Hund's case (c) to (e) which gave improved agreement with experimental total yield results for Rydberg orders from 10 to 14 [16].…”

“…The purpose of this paper is to report on an extension of the previous rotationally resolved studies on HI [9,11,16,22] by performing now angle-resolved measurements of the spin polarization components to obtain the dynamical parameters A, 0~, and ~. Furthermore, resuits for the asymmetry parameter p of the photoelectron angular distribution were obtained for the same expansion conditions of the molecular beam and the measurements of the angle-integrated spin polarization were extended to higher photon energies.…”

“…Several theoretical studies covering different aspects of the photoionization of the HI molecule are available for the spin-orbit autoionization region [ 16,19,20,21]. After the first multichannel quantum-defect calculation of the polarization parameters [ 19] a formalism which includes the molecular rotation explicitly was developed by Raseev and Cherepkov [20].…”

“…Several Rydberg series converging to the higher lying 2/71/2 component autoionize through spin-orbit interaction into the 21-13/2 continuum. The large rotational constant of the neutral molecule (B e' = 6.426 cm-1) [15] and the similar value for the molecular ion (B + ~6.3 cm-1) [16] lead to a simple rotational structure in the ionization spectra. This structure can be resolved quite readily in the excitation step using narrow-band VUV radiation generated by frequency mixing.…”