The Mechanism of Magnetically Tuned Singlet–Triplet Avoided Crossings in the Ã1A2–X̃1A1 410 Band of Thioformaldehyde H2CS

✍ Scribed by W. Ulrich; W. Hüttner

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 307 KB
• Volume: 200
• Category: Article
• ISSN: 0022-2852
• DOI: 10.1006/jmsp.2000.8063

✦ Synopsis

Magnetically tuned singlet-triplet perturbations in the 4 1 A ˜1A 2 -2 1 3 1 a ˜3A 2 system of thioformaldehyde, found in orthorotational states (I ϭ 1, the two hydrogen spins parallel) have been identified as being caused by vibronic spin-orbit coupling. This perturbation mechanism has been confirmed in several avoided crossings observed in this work for para states (I ϭ 0, hydrogen spins antiparallel) which are much stronger. Parametrization of the theory has led to a quantitative understanding of the experimental frequency-field relations, and to an accurate prediction of the rovibrational energies of the triplet state. This in turn permitted the detection of about 100 Doppler-limited 2 1 3 1 a ˜3A 2 -0 0 X ˜1A 1 rovibronic transitions which led into fine structure states. The combined data was then used to determine a set of rotational, fine, and hyperfine triplet-state parameters, the term value T 0 (2 1 3 1 a ˜3A 2 ) ϭ (16 685.385 Ϯ 0.002) cm Ϫ1 , and the spin-orbit vibronic singlet-triplet coupling constant, W ST ϭ (0.0691 Ϯ 0.0016) cm Ϫ1 . A large number of frequency perturbations observed in the crossings, ranging from 2 to 300 MHz, can be explained with this single parameter.