A MOLECULE OF THE FORM CH(2)X MAY BE RESPONSIBLE FOR MANY OF THE DIFFUSE INTERSTELLAR BANDS - A DISCUSSION OF THIOFORMALDEHYDE

Only recently have groups of diffuse interstellar bands (DIBs) been ob served to have regular structure lending new hope for the identificati on of the bands' origins. Herbig has reported a group of bands between 6770 and 6860 Angstrom which seem to show regular spacing and intensi ty alternation. We suggest that these bands resemble perpendicular vib ronic bands in a molecule of the form CH(2)X. As the Herbig group lies very near an expected transition of similar form in thioformaldehyde, CH2S, an analysis of the absorption spectrum of that molecule was mad e to determine if it had other bands in common with the DIB spectrum, Six prominent, red-shaded, sharp, single-headed bands were calculated, based on laboratory data, to have absolute frequency positions within 2 cm(-1) of those for the corresponding DIBs. The transitions would o riginate from the 2 nu(3) level in the ground electronic state of thio formaldehyde, suggesting that vibrationally hot bands in the transitio n (A) over tilde(1)A(2) < -(X) over tilde(1)A(1), may correspond to a number of DIBs. Although no absorption features are seen from a vibrat ionally cold ground state, only a few thioformaldehyde bands expected to be more intense than those suggested to be in the DLB spectra have not been observed to date. There are no significant inconsistencies be tween corresponding thioformaldehyde bands and DIBs with respect to es tablished DIB families. The corresponding bands also generally agree i n their shapes and expected intensities. The DIBs appear slightly narr ower than the thioformaldehyde bands even if the latter were from a ro tationally cold molecule.