The A2Δ–X2Π band system of the CD radical

Abstract

The A2Δ–X2Π, Δv=0 sequence of the CD radical was observed in the 22800–24000cm−1 spectral region using a conventional spectroscopic technique. The CD molecules were formed and excited in a stainless steel hollow-cathode lamp with two anodes and filled with a mixture of He buffer gas and CD4. The emission from the discharge was observed with a plane-grating spectrograph and recorded using a photomultiplier tube. The observed lines were assigned to the 0–0, 1–1, 2–2, and 3–3 bands. In total, 1189 transition wavenumbers were precisely measured, with an estimated accuracy of 0.003cm−1, and rotationally analyzed. In the final global fit, the present data were combined with available high-resolution measurements of the vibration–rotation transitions [Morino et al., J. Mol. Spectrosc. 174 (1995) 123–131] and pure rotational transitions [Brown and Evenson, J. Mol. Spectrosc. 136 (1989) 68–85; Halfen et al., Astrophys. J. 687 (2008) 731–736]. This procedure enabled the extraction of molecular constants for the A2Δ and X2Π states of CD. The equilibrium parameters were compared with the calculations performed using the Born–Oppenheimer approximation, and a slight difference was observed in some cases due to the partial breakdown of the B–O approximation. The electronic isotopic shift, Δνe, for the A–X transition was determined to be 32.105cm-1, and the shift independent of the nuclear mass coefficient, ΔU=64.762(38)cm-1, was also calculated.