Description

No field-free rotational transitions have been measured for silylidyne. An extensive set of infrared transitions has been published by
(1) M. Betrencourt, D. Boudjaadar, P. Chollet, G. Guelachvili, and M. Morillon-Chapey, 1986, J. Phys. Chem. 84, 4121.
Electronic A2Δ – X2Π transitions were reported by
(2) R. S. Ram, R. Engleman Jr., and P. F. Bernath, 1998, J. Mol. Spectrosc. 190, 341.
These data were subjected to a combined fit. A small number of transitions with large residuals has been omitted from the fit. Two of the four main hyperfine coupling parameters were determined experimentally in
(3) J. M. Brown, R. F. Curl, and K. M. Evenson, 1984, J. Phys. Chem. 81, 2884;
the remaining two were estimated based on ab initio calculations. The resulting predictions are sufficiently accurate, but should, nevertheless, be viewed with some caution.
SiH is closer to Hund's case (a) at small quantum numbers. The ground state spin-flip transitions are weak for SiH; they are predicted near 4540.6 and 4543.4GHz. These transitions are much stronger in CH, were they occur near 532.8 and 536.8GHz.
The ab initio ground state dipole moment was taken from
(4) W. Meyer and P. Rosmus, 1975, J. Phys. Chem. 63, 2356.
These appear to represent the only high-level calculations involving vibrational corrections which are very important because of the very small size of the dipole moment.