The A2Δ–X2Π band system of the CD radical

The A 2Δ-X 2Π, Δv = 0 sequence of the CD radical was observed in the 22 800-24 000 cm -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 CD 4. 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 0.003 cm -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 A 2Δ and X 2Π 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, Δν e, 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. © 2012 Elsevier Inc.