Fourier transform microwave spectroscopy coupled with a discharge-assisted laser ablation source (DALAS) has been used to record the J = 1 → 0 pure rotational transitions of Sc¹⁴N, Sc¹⁵N, Y¹⁴N, Y¹⁵N, and Ba¹⁴NH (X¹Σ⁺). Each species was synthesized by the reaction of the ablated metal with either NH₃ or ¹⁵NH₃ in the presence of a DC discharge. For each species hyperfine structure was resolved. In the case of ScN and YN hyperfine parameters (quadrupole and nuclear spin-rotation) for the metal and nitrogen were determined and for BaNH the nitrogen quadrupole coupling constant was measured. These hyperfine constants are interpreted to gain insight into the metal-nitrogen bonding in each species. In addition, DFT calculations were performed to assist with the assignment of each spectrum and the characterization of the metal-nitrogen bond.

The N = 2 ← 1 transition of the CrH (X⁶Σ⁺) radical near 730-734 GHz and the J = 2 ← 1 line of AlH (X¹Σ⁺) near 755 GHz have been measured using submillimeter/Terahertz direct absorption spectroscopy. CrH was created in an AC discharge of Cr(CO)₆ vapor and H₂ in the presence of argon. AlH was produced from Al(CH₃)₃ vapor and H₂ in argon with an AC discharge. In addition, three fine structure components of the N = 1 ← 0 transition of the SH⁺ (X³Σ⁻) cation from 345-683 GHz were recorded. SH⁺ was generated from H₂S and argon in an AC discharge. The data have been analyzed, and spectroscopic constants for these species have been refined. These parameters are in excellent agreement with past millimeter, infrared, and optical data. SH⁺ is a known interstellar molecule, and these measurements confirm recent observations of this species. The new data for CrH and AlH could facilitate the detection of these species in interstellar/circumstellar gas.

The new linear molecule Ag-C ≡ C-Cl has been detected and characterized by means of rotational spectroscopy. It was synthesized by laser ablation of a silver rod in the presence of a gaseous sample containing a low concentration of CCl₄ in argon, cooled to a rotational temperature approaching 2 K through supersonic expansion and analyzed by chirped pulse Fourier transform microwave spectroscopy. Substitution coordinates are available for the silver and chlorine positions and will be compared to ab initio calculations at the CCSD(T)/aug-cc-pV5Z level of theory. The Ag-¹³C ≡ ¹³C-Cl isotopologue was also observed using a similar gas mixture containing ¹³CCl₄. The Cu analogue Cu-C ≡ C-Cl was similarly identified and characterized.

The pure rotational spectra of 8 isotopologues of H₃N···AgI and 6 isotopologues of (CH₃)₃N···AgI were measured in a chirped pulse Fourier-transform microwave spectrometer. The complexes were synthesized in a molecular beam from a gas sample containing H₃N or (CH₃)₃N and CF₃I precursors diluted in argon. Laser ablation was used to introduce silver atoms to the gas phase. The rotational constant B₀, centrifugal distortion constants D_J and D_JK, and the nuclear quadrupole coupling constant χ_aa(I) have been determined for (CH₃)₃^14/15N···^107/109AgI, (CD₃)₃N···^107/109AgI, H₃^14/15N···^107/109AgI and D₃N···^107/109AgI by fitting the measured transitions to a symmetric top Hamiltonian. The spectroscopic constants (B₀+ C₀), ∆_J and χ_aa(I) have been determined for D₂HN···^107/109AgI through fits that employed a Hamiltonian appropriate for a very near prolate asymmetric rotor. Partial effective (r₀) and substitution (r_s) structures have been determined.

A chirped-pulse Fourier transform microwave spectrometer has been used to measure the microwave spectra of both C₂H₂…AgI and C₂H₄…AgI. These complexes are generated via laser ablation at 532 nm of a silver surface in the presence of CF₃I and either C₂H₂ or C₂H₄ and argon and are stabilized by a supersonic expansion. Rotational (A₀, B₀, C₀) and centrifugal distortion constants (∆_J and ∆_JK) of each molecule have been determined as well the nuclear electric quadrupole coupling constants the iodine atom (χ_aa(I) and χ_bb−χ_cc(I)). The spectrum of each molecule is consistent with a C_2v structure in which the metal atom interacts with the π-orbital of the ethene or ethyne molecule. Isotopic substitutions of atoms within the C₂H₂ or C₂H₄ subunits are in progress and in conjunction with high level ab initio calculations will allow for accurate determination of the geometry of each molecule. These to complexes are put in the context of the recently studied H₂S…AgI,S.Z. Riaz, S.L. Stephens, W. Mizukami, D.P. Tew, N.R. Walker, A.C. Legon, Chem. Phys. Let., 531, 1-12 (2012)C…AgI,S.L. Stephens, W. Mizukami, D.P. Tew, N.R. Walker, A.C. Legon, J. Chem. Phys., 136(6), 064306 (2012) H₃N…AgI and (CH₃)₃N…AgI.D.M. Bittner, D.P. Zaleski, S.L. Stephens, N.R. Walker, A.C. Legon, Study in progress.html:<hr /><h3>Footnotes: S.Z. Riaz, S.L. Stephens, W. Mizukami, D.P. Tew, N.R. Walker, A.C. Legon, Chem. Phys. Let., 531, 1-12 (2012)O S.L. Stephens, W. Mizukami, D.P. Tew, N.R. Walker, A.C. Legon, J. Chem. Phys., 136(6), 064306 (2012), D.M. Bittner, D.P. Zaleski, S.L. Stephens, N.R. Walker, A.C. Legon, Study in progress.

The chemi-ionization reaction Sm + O → SmO⁺ + e⁻ has been used for chemical release experiments in the thermosphere. This reaction was chosen, in part, because the best available data indicated that it is exothermic by 0.35 ± 0.12 eV. Low ion yields in the initial atmospheric release experiments raised questions concerning the accuracy of the ionization energy (IE) for SmO and the bond dissociation energy (BDE) of SmO⁺. New measurements of the BDE, obtained using a selected ion flow tube and guided ion beam techniques, yielded a more precise value of 5.73 ± 0.07 eV. The ionization energy of SmO was reexamined using pulsed-field ionization zero kinetic energy (ZEKE) photoelectron spectroscopy. The value obtained, 5.7427 ± 0.0006 eV, was significantly higher than the literature value. Combined with literature bond energies of SmO, this IE indicates an exothermicity for Sm + O → SmO⁺ + e⁻ of 0.14 ± 0.17 eV, independent from and in agreement with the value deduced from the guided ion beam measurements. The implications of these results for interpretation of chemical release experiments are considered.

The bonding and electrostatic properties of gold containing molecules are highly influenced by the large relativistic and electron correlation effects.P. Pyykko; Angew Chem. Int[43] , 4412,(2004).ere we report on the electricpermanent dipole moment measurement and hyperfine interaction analysis of the ²∆_3/2-²Π_3/2 and ²∆_5/2-²Π_3/2 bands of AuS. A cold molecular beam sample of gold sulfide was generated using a supersonic laser ablation source. The electronic bands were recorded at high resolution (35 MHz, FWHM) using laser excitation spectroscopy both field-free and in the presence of a static electric field. The observed hyperfine spectral features were assigned and a set of spectroscopic parameters for the ²∆ and ²Π states were obtained. The Stark induced shifts of selected low-rotational features were analyzed to determine the permanent electric dipole moments in both the ground and excited states.

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Footnotes:

P. Pyykko; Angew Chem. Int[43] , 4412,(2004).H

A revision of the value for the Cu nuclear quadrupole moment (NQM) is reported based on high-accuracy ab initio calculations on the Cu electric field gradients in the CuF and CuCl molecules. Electron-correlation effects have systematically been taken into account using a hierarchy of coupled-cluster methods including up to quadruple excitations. It is shown that the CCSD(T)_Λ method provides a more reliable treatment of triples corrections for Cu electric-field gradients than the ubiquitously applied CCSD(T) method, which is tentatively attributed to the importance of the wavefunction relaxation in the calculations of a core property. Augmenting large-basis-set CCSD(T)_Λ results with the remaining corrections obtained using additive schemes, including full triples contributions, quadruples contributions, zero-point vibrational corrections, spin-orbit corrections, as well as the correction from the Gaunt term, a new value of 209.7(50) mbarn for the Cu NQM has been obtained. The new value substantially reduces the uncertainty of this parameter in comparison to the standard value of 220(15) mbarn obtained from a previous muonic experiment.

Mass-selected copper-acetylene cation complexes of the form Cu(C₂H₂)_n+ are produced by laser ablation and studied via infrared laser photodissociation spectroscopy in the C-H stretching region (3000-3500 cm⁻¹). Spectra for larger species are measured via ligand elimination, whereas argon tagging is employed to enhance dissociation yields in smaller complexes. The number of infrared active bands, their frequency positions and their relative intensities provide insight into the structure and bonding of these ions. Density functional theory calculations are carried out in support of this work. The combined data show that cation-π bonds are formed for the n=1-3 species, resulting in red-shifted C-H stretches on the acetylene ligands. Three acetylene ligands complete the coordination of the copper cation. Additional ligands (n=4-6) solvate the n=3 core by forming CH-pi bonds. Distinctive vibrational patterns are exhibited for coordinated vs. solvent ligands. Theory reproduces these results.

Anion photoelectron spectra and density functional calculations are reported for NbCr(CO)₂⁻ and NbCr(CO)₃⁻ complexes prepared by addition of Cr(CO)₆ vapor to a flow tube equipped with a niobium cathode discharge source. Electron affinities (± 0.007 eV) are measured to be 1.668 eV for NbCr(CO)₂ and 1.162 eV for NbCr(CO)₃, values which exceed the 0.793 eV electron affinity previously measured for ligand-free NbCr. The vibrationally-resolved 488 nm photoelectron spectra are compared with Franck-Condon spectra predicted for various possible isomers and spin states of the anionic and neutral metal carbonyl complexes. Results are also compared with photoelectron spectra of the corresponding chromium carbonyl complexes and of NbCr and NbCr⁻, which have formal bond orders of 5.5 (²∆) and 6 (¹Σ⁺), respectively. These comparisons help to elucidate the effects of sequential carbonylation on this multiple metal-metal bond, and of the formation of this bond on the chromium-carbonyl interactions.

La atom reactions with 1-pentyne (CH ≡ CCH₂CH₂CH₃) and 1,4-pentadiene (CH₂=CHCH₂CH=CH₂) were carried out in a laser-ablation molecular beam source. La(C₅H₆) was observed in the two reactions through time-of-flight mass spectrometry and characterized by mass-analyzed threshold ionization spectroscopy. The most stable isomer of La(C₅H₆) was identified as a six-membered metallacycle, La(CH₂CH=CHCH=CH), with La binding to the two terminal carbon atoms of the unsaturated hydrocarbon. The metallacycle is formed by hydrogen elimination and migration induced by the La atom. The neutral complex with C₁ symmetry has a doublet ground state, and the corresponding ion has a singlet state generated by the removal of a La 6s-based electron. The adiabatic ionization energy of the metallacycle was determined to be 37941 (5) cm⁻¹. Three vibrational modes of the ion were measured to be 318, 407, and 538 cm⁻¹, which correspond to the La-ligand stretching, carbon skeleton bending with CH₂ rocking, and carbon skeleton bending with CH₂ twisting, respectively. In addition, two hot bands were observed at 276 and 367 cm-1 below the origin band and identified to be the vibrational frequencies of the La-ligand stretching and carbon skeleton bending with CH₂ rocking modes of the neutral complex.