Electronic spectroscopy of the A˜1A″↔X˜1A′ system of CDCl

We report fluorescence excitation and single vibronic level emission spectra of the A˜1A″↔X˜1A′ system of CDCl in the 500-740 nm region, measured under jet-cooled conditions using a pulsed discharge source. A total of 29 cold bands involving the pure bending levels 20n (n = 2-11), C-D stretching fundamental (101), and combination bands 20n301 (n = 2-10), 20n302 (n = 9), 10120n (n = 2-8), and 10120n301 (n = 7) were observed; most of these are reported here for the first time. Rotational analysis typically yielded band origins and rotational constants for both isotopomers (CD35Cl, CD37Cl). The derived A˜1A″ vibrational intervals are combined with previous studies at lower energy to determine excited state barriers to linearity for the 2n, 2n31, and 112n progressions. The A˜1A″ state C-D stretching frequency (2229.6 cm−1) is determined here for the first time, in excellent agreement with ab initio theory. Following our observation of new bands in this system, we obtained single vibronic level (SVL) emission spectra which probe the vibrational structure of the X˜1A′ state up to ∼8000 cm−1 above the vibrationless level. The total number of X˜1A′ and a˜3A″ levels observed is more than twice that previously reported, and a complete set of Dunham parameters was determined for the X˜1A′ state of CD35Cl and CD37Cl. Comparisons with previous experimental and recent high level ab initio studies are reported. Our results shed new light on the vibrational structure of the X˜1A′, A˜1A″, and a˜3A″ states of CDCl, and, more generally, spin-orbit coupling in the monohalocarbenes.