The laser induced fluorescence spectrum of jet-cooled CoC near 750 nm has been measured at high resolution following the reaction of laser-ablated cobalt atoms with methane. The X 2 ⌺ ϩ ground state of CoC is an unusually good example of Hund's case (b ␤S ) coupling. Since Co has a nuclear spin Iϭ7/2, each rotational level is split by the Fermi contact interaction into Gϭ3 and Gϭ4 components, where G‫؍‬I؉S; the splitting for Nϭ0 is more than 0.5 cm Ϫ1. The X 2

No abstract

No abstract

High sensitivity and precision spectroscopy in the far infrared AIP Conf.The laser excitation spectrum of tungsten methylidyne, WCH, has been recorded in the 12 000-15 400 cm Ϫ1 region. A total of 14 vibronic bands of WCH and 16 bands of WCD have been observed in this region. Rotational analysis shows that the ground state is X3/2( 2 ⌬), with the substitution structure r 0 ͑WwC͒ϭ1.7366 5 Å and r 0 ͑C-H͒ϭ1.076 5 Å. The excited vibronic levels have been assigned, on the basis of their WCH/WCD isotope shifts and their wavelength resolved fluorescence patterns, to three electronic states, Ã3/2( 2 ⌬), B1/2( 2 ⌸), and C 5/2( 2 ⌽), at 12 090, 13 392, and 14 110 cm Ϫ1 , respectively. The wavelength resolved fluorescence spectra have also established the low-lying vibrational levels of the ground state. The ground state bending fundamental lies at 660 cm Ϫ1 , while the W-C stretching frequency is 1006 cm Ϫ1 ; the corresponding frequencies in WCD are 501 cm Ϫ1 and 953 cm Ϫ1 , respectively. No evidence for the C-H stretching frequency has been found. Emission has also been observed to a low-lying electronic state, 813 cm Ϫ1 above the X3/2 state. The pattern of rotationally resolved emission to this state clearly indicates that it is a 4 ⌺ 1/2 state. Its bending frequency is 612 cm Ϫ1 , and its W-C stretching frequency is 971 cm Ϫ1 , indicating a slightly longer bond length than in the X3/2 state. High resolution cw laser spectra of the ͑0,0͒ bands of the two lowest excited electronic states ͓Ã3/2( 2 ⌬) and B1/2( 2 ⌸)͔ reveal a small splitting of the four principal tungsten isotopes ͑ 182 W, 183 W, 184 W, and 186 W͒ which serves to confirm the presence of tungsten in the carrier. Hyperfine splitting associated with the 183 W nucleus (Iϭ1/2) has been observed for the ͑0,0͒ band of the Ã3/2ϪX3/2 system, allowing the electron configuration of the ground state to be elucidated.

The first transition metal complexes containing a formal metal-carbon triple bond were synthesized in 1973 by Fischer et al.;l their general formula was X-M(C0)4'CR [M = Cr, Mo, W; X = F, C1, Br, I; R = Me, Ph]To date, most of the compounds of this type that have been prepared are octahedral complexes of the group 6 metals (Cr, Mo, W), although some four-and five-coordinated structures also exist. X-ray and neutron diffraction measurements show that the MEC bond lengths are typically 1.65-1.75 8, for first row transition metals (Cr, Mn, Fe), and 1.75-1.90 8, for second (Mo) and third row transition metals (Ta, W, Os). We have recently identified an example of the simplest possible type of metal carbyne complex, a linear triatomic molecule consisting of a transition metal atom bonded to a CH group. The gas-phase electronic spectrum of the transient radical VCH has been recorded in the 600-800 nm region following the reaction of laser-ablated vanadium atoms with methane. Only two other triatomic transition metal containing molecules, CuOH2 and YNH,3 have been definitely identified by their gas-phase electronic spectra; VCH is the first carbyne. Its molecular structure has been determined by isotope substitution, and two of its three vibrational frequencies have been measured.The experimental apparatus follows the design of Simard et aL4 Briefly, a rotating vanadium rod (Goodfellow 99.8%+) was ablated with 900 pJ/pulse of 532 nm radiation from a Nd: YAG laser. The V atoms were entrained in a pulse of highpressure "oxidant" gas (80 psi of He containing 5-10% C&) and expanded into the vacuum of the apparatus, forming a supersonic jet-cooled molecular beam. A tunable probe laser beam, -5 cm downstream, excited molecular fluorescence, which was passed through a monochromator (to eliminate emission from unwanted impurities) and recorded with a cooled photomultiplier tube. Survey spectra were obtained using a Lumonics HD500 tunable pulsed dye laser, pumped by a second Nd:YAG laser; high-resolution spectra, with a line width of about 90 MHz, were recorded with a Coherent Inc. Model 899-21 ring laser, pumped by an Ar+ laser. ' Present address: Masoni, C.; Hackett, P. A. J . Mol. Spectrosc. 1989, 136, 44-55.F.912 J'=1 7/2 512 512 112 912 j ' = c _ 0.025 m-' R(J,W 1 1 1 1 1 1 1 1 1 1 1 1 Q(J) 13517) 91 P(J) 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Figure 1. Medium-resolution spectrum (0.1 cm-I line width) of the 3A1 -X3A1 sub-band of VCH at 800.5 nm. The hyperfine structure of the Q(l) line, recorded at high resolution (0.003 cm-' line width), is shown above. The energy level diagram illustrates the splittings given by the vanadium nucleus and their quantum number assignments; the doubling caused by the proton is only resolved for the longest wavelength component.Representative spectra are given in Figure 1. The figure shows the longest wavelength band of VCH that we have found, near 800 nm, together with the nuclear hyperfine structure of the first Q branch line, Q(1). The hyperfine patterns, which are characteristic for a nucleus ...