High resolution laser spectroscopy of the C̃ 2Δ–X̃ 2Σ+ transition of CaOH and CaOD: Vibronic coupling and the Renner–Teller effect

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Abstract
The C̃ 2Δ–X̃ 2Σ+ transition of CaOH and CaOD has been observed in the blue region of the spectrum. This electronically forbidden transition becomes allowed through vibronic coupling with the bending mode. The (010)–(000) band for CaOH and the (010)–(000), (020)–(010), (010)–(010), (000)–(010), and (010)–(0200) bands for CaOD have been recorded and analyzed at high resolution. The C̃ 2Δ(000) state of CaOD has a band origin at 21 907.128(1) cm−1, a rotational constant B of 0.293 536(7) cm−1, and a spin–orbit constant A of 11.4944(5) cm−1. A rotational analysis of the C̃ 2Δ(020)μΣ and the C̃ 2Δ(020)κΣ states of CaOD has also led to the first experimental determination of the Renner–Teller parameter ĝ4 for a 2Δ state at ĝ4=−0.038 62(9) cm−1.