Dl. Joo et al., Experimental proof of the case (ab) coupling hypothesis in the first excited triplet state of selenoformaldehyde (H2C=Se), J CHEM PHYS, 112(5), 2000, pp. 2285-2291
A high-resolution laser-induced phosphorescence spectrum of the vibronicall
y induced 4(0)(1) band of the (a) over tilde (3)A(2)-(X) over tilde (1)A(1)
system of (D2CSe)-Se-80 has been recorded with Doppler-limited resolution.
Rotational analysis revealed that transitions to all three spin components
occur within the 12 265-12 525 cm(-1) region. The rotational structure of
the band was fitted to the experimental precision of measurement using a tr
iplet state Hamiltonian that allowed for slight variations in the geometrie
s of the individual spin components. The results show that the triplet stat
e of selenoformaldehyde involves case (ab) coupling, in which two of the sp
in components are close together and the third is ca. 125 cm(-1) higher in
energy. This unusual occurrence of large zero-field splittings in the tripl
et state of an asymmetric top arises because of the close proximity of the
(3)A(1)(pi,pi*) state which substantially displaces two of the spin compone
nts to lower energy. (C) 2000 American Institute of Physics. [S0021-9606(00
)01105-3].