| Spectra of zirconium monocarbide (ZrC), zirconium methylidyne (ZrCH) and lanthanum imide (LaNH) are reported for the first time. All species have been produced under jet-cooled conditions by reaction of gaseous metal atoms with methane or ammonia and examined via laser-induced fluorescence.;ZrC has several electronic states below 2500 cm-1: X3Sigma+ and three 1Sigma + states, which appear to represent all possible arrangements of two electrons in the nearly degenerate 11sigma and 12sigma orbitals (from Zr 5ssigma + C 2psigma). For X 3Sigma+ (r0 = 1.807 A), the small spin-spin constant (lambda0 = 0.514 cm-1) and large Fermi contact parameter of 91Zr12C (IZr = 5/2) indicate the configuration (11sigma)1(12sigma) 1. The tightly bound a1Sigma+ state (T0 = 187.83 cm-1, r0 = 1.739 A) has the configuration (11sigma)2, while anomalous vibrational intervals and 12C/13C isotope shifts of the other two states reveal their isosymmetry. This orbital scheme also accounts for the complex structure above 16000 cm-1; identical, strongly interacting manifolds result from promoting either sigma electron to the same orbital.;ZrCH has a 2&Pgr;--X2Sigma + electronic system in the visible region analogous to that seen for isoelectronic ZrN, but they otherwise share little similarity. For X˜ 2Sigma+, high-resolution rotational analyses give r0 bond lengths, while dispersed fluorescence has characterised its vibrational structure. Conversely, many details remain unclear for the excited state. Upper state P = Lambda + ℓ + Sigma values and Zr isotope shifts have been obtained for many subbands of ZrCH and ZrCD; 12C/ 13C shifts have also been determined for some ZrCH bands. Unexpectedly small values of the spin-orbit constant and Zr-C stretching frequency, and the large Renner-Teller splitting in the 010--000 band are believed to be due to strong vibronic coupling with 2Sigma and 2Delta states.;The electronic structure of LaNH is similar to isoelectronic LaO, with the added complication of vibronic coupling between the A2&Pgr; and B˜2Sigma+ states. This is apparent from anomalies in the B˜2Sigma+--X˜ 2Sigma+ hyperfine intensity profiles (ILa = 7/2), the Hund's case (a) coupled B˜2Sigma +(0&ugr;20) level structure and the large B˜ 2Sigma+ state bending frequency. |
