Laser-Induced Fluorescence of Gaseous Vanadium Methylidyne, VCH: A Triatomic Organometallic Molecule

Abstract

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 ...

Communication: State-to-state photoionization and photoelectron study of vanadium methylidyne radical (VCH)

“…1. Although the resolution of this spectrum was significantly lower than that achieved in the previous higher resolution study 3 of Barnes et al, we are still able to identify several well-resolved rotational transitions. The assigned rotational transitions for the P, Q, and R branches as marked on top of the excitation spectrum were based on spectral simulation using the spectroscopic constants reported 3 previously.…”

“…1 Previous rotationally resolved spectroscopic studies have provided precise spectroscopic constants and thus structural parameters for many neutral MC and MCH species. [2][3][4][5][6][7][8] However, similar rotationally resolved spectroscopic studies on MC + and MCH + ions are lacking. We have recently succeeded in performing high-resolution pulsed field ionizationphotoelectron (PFI-PE) 9, 10 studies for diatomic MX + (X = C, O, and N) species based on two-color visibleultraviolet (VIS-UV) excitation scheme, which has allowed fully rotationally selected and resolved spectroscopic measurement for MX + cations.…”

“…This communication presents such a highresolution photoelectron study for vanadium methylidyne cation (VCH + ) using the infrared (IR)-UV-PFI-PE method. The previous high-resolution spectroscopic study 3,4 ) have also been determined. 3 The highly precise IE(VCH) determined here, together with the known IE(V) 17 and IE(VC), 16 is most valuable for benchmarking theoretical energetic predictions 10,18 for the VCH/VCH + system because the 0 K bond dissociation energies (D 0 's) for the V + -CH and V-CH bonds are related to the IE(V) and IE(VCH) by the relation, D 0 (V + -CH) − D 0 (V-CH) = IE(V) − IE(VCH) based on conservation of energy.…”

Millimeter-wave spectroscopy of CrC (X3Σ−) and CrCCH (X̃ 6Σ+): Examining the chromium-carbon bond

“…VCH and TiCH have also been studied in the optical regime by Merer and collaborators, who found their structures to be linear. 21,22 The pure rotational spectrum of CuCH 3 has additionally been measured, revealing its C 3v symmetry. 23 Vibrationally resolved spectra of NiCH 3 has also been recorded.…”

Submillimeter-wave spectroscopy of VN (X3Δr) and VO (X4Σ−): A study of the hyperfine interactions

“…In addition, important aspects of chemical bonding in this element can be deduced from spectroscopic studies. Unfortunately, only a limited number of vanadium-containing species have been investigated spectroscopically to date at any resolution; these species include VN, VO, VF, VS, VCl, VCl + , and VCH [4][5][6][7][8][9][10]. Of these species, only three have been studied by rotational methods.…”