Microwave spectroscopy of platinum monofluoride and platinum monochloride in the X 2Π(3/2) states.

Platinum monofluoride (PtF) and platinum monochloride (PtCl) were detected in the gas phase using a source-modulated microwave spectrometer. The PtF and PtCl radicals were generated in a free space cell using the sputtering reaction from a platinum sheet placed on the inner surface of a stainless steel cathode through a dc glow discharge plasma of CF(4) and Cl(2), respectively, diluted with Ar. Rotational transitions were measured in the region between 150 and 313 GHz. Rotational, centrifugal distortion, and several fine- and hyperfine-structure constants were determined by a least-squares analysis. The observed fine-structure spectral patterns indicate that both PtF and PtCl radicals have the (2)Π(3/2) electronic ground states, while the related cyanide PtCN and hydride PtH radicals have the (2)Δ(5/2) electronic ground states.

Low-energy vibrations of the group 10 metal monocarbonyl MCO (M = Ni, Pd, and Pt): rotational spectroscopy and force field analysis.

The rotational spectra of NiCO and PdCO in the ground and ν(2) excited vibrational states were observed by employing a source-modulated microwave spectrometer. The NiCO and PdCO molecules were generated in a free space cell by the sputtering reaction of nickel and palladium sheets, respectively, lining the inner surface of a stainless steel cathode with a dc glow plasma of CO and Ar. The molecular constants of NiCO and PdCO were determined by least-squares analysis. By force field analysis for the molecular constants of not only NiCO and PdCO but also of PtCO as previously reported, the harmonic force constants were determined for these three group 10 metal monocarbonyls. The vibrational wavenumbers derived for the lower M-C stretching vibrations were in good agreement with those obtained from the IR spectra in noble gas matrices and those predicted by several quantum chemical calculations published in the past. The bending vibrational wavenumbers derived by the force field analysis were also consistent with most quantum chemical calculations previously reported, but showed systematic discrepancies from the matrix IR values by about 40 cm(-1), even after reassignment (ν(2) band → 2ν(2) band) of the matrix IR spectra of PdCO and PtCO.

Hyperfine resolved Fourier transform microwave and millimeter-wave spectroscopy of the iodomethyl radical, CH2I (X2B1).

Fourier-transform microwave and millimeter-wave spectra of the iodomethyl radical, CH(2)I, have been observed in the ground vibronic state in the frequency ranges 17-38 GHz and 200-610 GHz, respectively. The pi-electron radical was produced either by iodine abstraction from diiodomethane (CH(2)I(2)) or by hydrogen abstraction from iodomethane (CH(3)I). Seventy-three hyperfine resolved lines owing to the two hydrogen and to the iodine nuclei have been detected in the microwave region, including K(a) = 0 (ortho species) and K(a) = 1 (para species). No hyperfine splitting due to the hydrogen nuclei could be observed for the para species, directly confirming the planarity of the radical and that the ground electronic state is (2)B(1). More than 400 a-type transitions that span the values N' < or = 35, K(a) < or = 6, were detected. A global least-squares analysis of the measured lines was conducted and led to the determination of an exhaustive list of molecular constants. In particular, the sign of the Fermi-contact constant of iodine was unambiguously determined to be negative, which is opposite to that of the other monosubstituted halomethyl radicals. This work allowed a systematic comparison of the structural and bonding properties among the CH(2)X analogues (where X = F, Cl, Br, and I) owing to the hyperfine coupling constants of both the hydrogen and halogen nuclei.

Detection of free monomeric silver(I) and gold(I) cyanides, AgCN and AuCN: microwave spectra and molecular structure.

The chemistry of the group 11 metal cyanide system has been of considerable interest because of the commercial importance of some of the complexes formed in this system. These metal cyanides contain one-dimensional linear -M-CN-M-CN-M- chains in the solid state; however, they have not been observed as free monomeric species. This Article reports the first detection of monomeric AgCN and AuCN in the gas phase by using rotational spectroscopy. The sputtering reaction of silver and/or gold sheets placed on a stainless steel cathode with CH3CN diluted in Ar resulted in the production of AgCN and AuCN spectra. Spectroscopic observation of the parent and several rare isotopic species allowed the determination of r(0), r(s), r(Iepsilon), r(m)(1), and r(m)(2) structures in the case of AgCN and r(0) and r(s) structures in the case of AuCN. All data indicate that these two species have a linear MCN geometry with a low-energy bending vibration.

Microwave spectroscopy of the PBr radical in the X (3)Sigma(-) state.

The microwave spectrum of the PBr radical in the X (3)Sigma(-) ground electronic state has been observed by a source modulated spectrometer. The PBr radical was generated in a free space cell by an acdc glow discharge in a mixture of PBr(3) with He andor H(2). A spectrum with three spin components for each of the two isotopomers, P(79)Br and P(81)Br, was observed. The spectrum showed hyperfine splitting caused by interactions due to both bromine and phosphorus nuclei. The molecular constants including the magnetic hyperfine and nuclear quadrupole hyperfine interaction constants were determined by analyzing the observed spectrum. The spin density of the unpaired electrons was estimated from the observed hyperfine coupling constants to be 85.4% and 16.3% on the phosphorus and bromine atoms, respectively.

The rotational spectrum of the NiS radical in the X3Sigma- state.

The rotational spectrum of the NiS radical in the X(3)Sigma(-) state was observed by employing a source-modulation microwave spectrometer. The NiS radical was generated in a free space cell by a dc glow discharge in H(2)S diluted with Ar. The nickel atoms were supplied by the sputtering reaction from a nickel cathode. Rotational transitions with J = 11-10 to 25-24 were measured in the region between 135 and 314 GHz. Rotational, centrifugal distortion and several fine-structure constants were determined by a least-squares analysis. Other spectroscopic parameters such as dissociation energy, vibrational wavenumber and equilibrium bond length were also derived from the determined molecular constants. Excitation energies of the lowest (3)Pi and (1)Sigma(+) states were estimated from the fine-structure constants, lambda and gamma.

The rotational spectrum of the NiI radical in the X 2Delta(5/2) and A 2Pi(3/2) states.

The millimeter- and submillimeter-wave spectra of the NiI radical in the X (2)Delta(5/2) and A (2)Pi(3/2) states were observed by a source-modulated microwave spectrometer. The NiI radical was generated by a dc glow discharge in the mixture of CH(3)I vapor and Ar gas through the sputtering reaction with a Ni cathode. Observed transition frequencies for each electronic state were independently analyzed using a polynomial energy expression based on Hund's case (c) approximation. The deperturbed rotational constants were also estimated by the perturbation analysis including interaction terms between the ground state and the lowest excited state.

Electronic properties of CrF and CrCl in the X 6Sigma+ state: observation of the halogen hyperfine structure by Fourier transform microwave spectroscopy.

The rotational spectra of the CrF and CrCl radicals in the X 6Sigma+ state were observed by employing a Fourier transform microwave spectrometer. The CrF and CrCl radicals were generated by the reaction of laser-ablated Cr with F2 and Cl2, respectively, diluted in Ar. A chromium rod made of chromium powder pasted with epoxy resin was ablated by a Nd:YAG laser. Rotational transitions were measured in the region between 8 and 26 GHz. Several hyperfine constants due to the halogen nuclei were determined by a least-squares analysis. The electronic properties of CrF and CrCl were derived from their hyperfine constants and were compared with those of other 3d transition metal monohalides: TiF, MnF, FeF, CoF, NiF, and FeCl.

Perturbation analysis for the rotational spectrum of the NiBr radical in the X2Pi3/2 and A2Delta5/2 states.

The millimeter- and submillimeter-wave spectra of the NiBr radical in the X (2)Pi(3/2) and A (2)Delta(5/2) states were observed by a source-modulated microwave spectrometer. The NiBr radical was generated in a dc glow discharge through the mixture of Br(2) vapor and Ar gas by the sputtering reaction with a Ni cathode. Observed transition frequencies were independently analyzed for both electronic states using a standard polynomial expression of a Hund's case (c) approximation. Anomalous behavior of the effective molecular constants in the X (2)Pi(3/2) state was interpreted as the result of the perturbation between the X (2)Pi(3/2) and A (2)Delta(5/2) states. The deperturbed molecular constants were derived using a simplified supermultiplet Hamiltonian including the interaction terms between the two electronic states.

Detection of free nickel monocarbonyl, NiCO: rotational spectrum and structure.

Unsaturated transition metal carbonyls are important in processes such as organometallic synthesis, homogeneous catalysis, and photochemical decomposition of organometallics. In particular, a metal monocarbonyl offers a zeroth-order model for interpreting the chemisorption of a CO molecule on a metal surface in catalytic activation processes. Quite large numbers of theoretical papers have appeared which predict spectroscopic and structural properties of transition metal carbonyls. The nickel monocarbonyl NiCO has been one of the metal carbonyls most extensively studied by the theoretical calculations. At least 50 theoretical studies have been published on this simplest transition metal carbonyl up to the present time. However, experimental evidence of NiCO is much more sparse than theoretical predictions, and the actual structure of NiCO has never been determined by any experimental methods. This Communication reports the first preparation of free nickel monocarbonyl and observation of its rotational transitions. The NiCO molecule was generated by the sputtering reaction of a Ni cathode in the presence of CO. The accurate bond lengths of Ni-C and C-O were experimentally determined from isotopic data and were compared with the theoretical predictions for the first time.

Microwave Spectroscopic Study of NiF in the Electronic Ground and Lowest Excited States.

The rotational spectra of NiF in the electronic ground (2)Pi state and the lowest electronically excited (2)Sigma state have been observed. The source of nickel atom was sputtering from a nickel electrode or nickel powder placed on a stainless steel electrode. The molecular constants have been determined by a least-squares analysis of the observed transition frequencies. The rapid increase in the Lambda-type splittings in the ground state reveals that the observed rotational transitions are ascribed to the spin substate (2)Pi(3/2). The rotational transitions corresponding to the other substate,(2)Pi(1/2), have not been observed. The large spin-rotation interaction constant gamma in the electronically excited (2)Sigma state is consistent with that from the electronic spectroscopy. Copyright 2001 Academic Press.