ELECTRONIC BANS SYSTEMS OF VCH IN THE 590-800 nm REGION

Abstract

A complicated system of about 30 bands in the 590-800 nm region has been discovered by laser excitation, following the reaction of laser-ablated vanadium atoms with methane under supersonic jet-cooled conditions. At least two electronic transitions must be present, since the most prominent bands are analysed so far have integer rotational quantum numbers, and clear ${^{51}}V$ nuclear hyperfine structure. The presence of hydrogen in the carrier is suggested by experiments with $CD_{4}$. but the simple linear-molecule sub-band structure indicates that the carrier is VCH, rather than $VCH_{3}$. The lower state of the strongest bands in an $\Omega = 1$ state, presumably $X_{3} \Delta_{1}$ by analogy with $VN^{1}$. Wavelength resolved fluorescence experiments reveal a highly structured vibrational level pattern in the ground state, with the most prominent peaks corresponding to levels at 146, 572, 840, 1118 and $1402 cm^{-1}$ frequency is probably the V-C stretching vibration, shifted down considerably from its value in the isoelectronic VN molecule. Consistent with this, rotational analysis has given $B^{\prime\prime} = 0$. $491 cm^{-1}$, which correspond to a V-C bond length of about 1.72 {\AA}, some some 0.15 A longer than in VN while the hypergine h parameter of the ground state $(-0.0083 cm^{-1})$ is less than half that of VN, The 572 and $1118 cm^{-1}$ levels seem to involve overtones of the bending vibration, distorted by orbital angular momentum effects, while the $146 cm^{-1}$ interval is provisionally assigned as the lowest spin-orbit interval of the ground state. Rotational perturbations are widespread throughout the system. cvcn in the bands near 800 nm. While the A-doubling in the $({^{3}}\Pi_{0}$) upper state of the 639 nm band is highly erratic.