CRDS study of auto-ionizing Rydberg states of argon in a microwave discharge This article is part of a Special Issue on Spectroscopy at the University of New Brunswick in honour of Colan Linton and Ron Lees.

Abstract

Optical transitions from two microwave discharge excited states of argon have been observed using cavity ring-down spectroscopy. These transitions originate on the high-lying levels, 3d[1/2] 1° and 3d[3/2] 2° , and terminate on the nf ′[5/2] Rydberg (n = 8 to 22) levels, which, except for n = 8, lie between the 2P3/2 and 2P1/2 ionization thresholds. In total, 24 such spectral lines have been observed. The quantum defect for the f ′ series has been measured and is compared to previously measured values. We observe a nearly threefold jump in line width in going from n = 8 to n = 9, below and above the 2P3/2 threshold, respectively. The line widths are broad and increase monotonically with n (above 9), in contrast to the narrowing of line widths usually observed. We cannot attribute this to a single source but conclude that collisional, quasielastic l-mixing of the nf ′[5/2] Rydberg states plays a significant role.