THIOFORMALDEHYDE - ROTATIONAL ANALYSES OF THE A1A2-X1A1 VISIBLE ABSORPTION SYSTEM

The A ̃1A2- X ̃1A1 electronic absorption spectra of CH2S and CD2S have been photographed under high resolution. Selected bands have been rotationally analyzed by least squares line fitting and by band contour methods. Improved rotational constants have been obtained for the ground states of CH2S and CD2S by use of combination differences. Bands of all three polarizations appear in the electronic spectrum. The type A origin band is magnetic dipole allowed, whereas the 401 band is type B. Perturbations are identified in the 000 and 301403 bands of CH2S. The rotational constant A in the upper state decreases rapidly, in accordance with theoretical calculations, as successive quanta of the inversion mode ν′4 are excited. The planar inertial defect has a small positive value in the zero level of the upper state although the molecule is slightly nonplanar; the r8 geometry is r(CH) = 1.082 A ̊, r(CS) = 1.701 A ̊, angle HCH = 120°, and the out-of-plane angle is approximately 10°. © 1979.