Ion-pair state spectroscopy of HgCl

Fluorescence excitation spectra of HgCl produced and cooled in a corona-excited supersonic jet discharge are presented. The dominant feature between ≈ 368 and 267 nm is an extensive vibrationally and isotopically resolved band system which is assigned to the B 2 Σ + (ν′) ← X 2 Σ + (ν″ = 0, 1, and 2) valence-to-ion-pair state transition of the radical. Transition wavenumbers for vibrational bands with 75 ≥ ν′ ≥ 21 and 2 ≥ ν″ ≥ 0 were measured, and B-state Dunham parameters were derived which are valid between 75 ≥ ν′ ≥ 0. The equilibrium bondlength for the B-state was determined to be 2.960(2) Å by Franck–Condon calculations. B–X Franck–Condon factors are tabulated which are expected to help in the interpretation of HgCl 2 photodissociation and HgCl laser spectra.