Carbenes of platinum and palladium, PtC₃ and PdC₃, were generated in the gas phase through laser vaporization of a metal target in the presence of a low concentration of a hydrocarbon precursor undergoing supersonic expansion. Rotational spectroscopy and ab initio calculations confirm that both molecules are linear. The geometry of PtC₃ was accurately determined by fitting to the experimental moments of inertia of twenty-six isotopologues.

Transitions measured by a chirped pulse Fourier transform microwave spectrometer in the frequency range 6.5-18.5 GHz have been fitted and tentatively assigned to the linear molecules FCPtF and FPtI, each in a ¹Σ electronic state. Laser ablation was used to introduce Pt into the gas phase from a metal rod with natural isotopic abundance. CF₃I was used as a source of C, F and I atoms. The products of reactions between the chemical precursors were cooled to a rotational temperature approaching 2K through supersonic expansion of the gaseous sample. Different isotopologues of Pt were observed. The spectra of other palladium and platinum containing complexes obtained in a similar way will be presented.

Cerium oxide is a good ionic conductor, and the conductivity can be enhanced with oxygen vacancies and doping. This conductivity may play an important role in the enhancement of noble or coinage metal toward the water-gas shift reaction when supported by cerium oxide. The ceria-supported platinum catalyst in particular has received much attention because of higher activity at lower temperatures (LT) compared to the most common commercial LT-WGS catalyst. We have used a combination of anion photoelectron spectroscopy and density functional theory calculations to study the interesting molecular and electronic structures and properties of cluster models of ceria-supported platinum. [Ce_xO_y]Pt_x′ ⁻ (x,x^′=1,2 ; y ≤ 2x^′) clusters exhibit evidence of ionic bonding possible because of the high electron affinity of Pt and the low ionization potential of cerium oxide clusters. In addition, Pt⁻ is a common daughter ion resulting from photodissociation of [Ce_xO_y]Pt_x′ ⁻ clusters. Finally, several of the anion and neutral clusters have profoundly different structures. These features may play a role in the enhancement of catalytic activity toward the water-gas shift reaction.

The pure rotational spectrum of the organozinc halide, ClZnCH₃ (~X¹A₁), has been measured using Fourier-transform microwave (FTMW) and millimeter-wave direct-absorption methods in the frequency range 10–296 GHz. This work is the first study of ClZnCH₃ by gas-phase spectroscopy. The molecule was created in a DC discharge from the reaction of zinc vapor, produced either by a Broida-type oven or by laser ablation, with chloromethane in what appears to be a metal insertion process. Rotational and chlorine quadrupole constants were determined for three zinc isotopologues. The Zn – Cl bond was found to be partly ionic and significantly shorter than in EtZnCl.

La(C₅H₈) was formed by La reaction with 1-pentene (CH₂=CH-CH₂-CH₃) in a laser-vaporization supersonic molecular beam source and characterized with mass-analyzed threshold ionization (MATI) spectroscopy. The MATI spectrum displays an origin band at 38988 (5) cm⁻¹and three vibrational intervals of 130, 294, and 415 cm⁻¹. The La(C₅H₈) complex is identified as a five-membered metallacycle in C₁ point group, with the doublet and singlet being the lowest energy states of the neutral and cation, respectively. The energy at 38998 cm⁻¹corresponds to the adiabatic ionization energy of the complex, and the three vibration intervals in the order of the frequency increase are assigned to the terminal CH₃ torsion, asymmetric La-ligand stretch, and symmetric La-ligand stretch excitation of the ion. The La + 1-penetene reaction will also be compared with La reactions with other five-carbon hydrocarbon molecules, such as isoprene, 1-pentyne, and 1,4-pentadiene.

The reaction between Y atom and ethylene (CH₂=CH₂) was performed in a laser-ablation supersonic molecular beam source. Y(C₂H₂), Y(C₂H₄), and Y(C₄H₆) were observed by time-of-flight mass spectrometry and investigated with mass-analyzed threshold ionization (MATI) spectroscopy and theoretical calculations. Y(C₂H₂) is formed by hydrogen elimination, Y(C₂H₄) by simple association, and La(C₄H₆) by C-C bond coupling and dehydrogenation. Both Y(C₂H₂) and Y(C₂H₄) have a C_2v triangular structure with a C=C double bond in Y(C₂H₂) and a C-C single bond in Y(C₂H₄). Y(C₄H₆) has a five-membered metallacyclic structure (C_s) with Y binding to the two terminal carbon atoms of butene, which is the exactly same as that of Y(C₄H₆) formed in the Y + 1-butene reaction. For all three complexes, ionization has a small effect on the metal-carbon bond lengths because the rejected electron has basically a Y 5s character. The adiabatic ionization energies are measured to be 45679(5) cm⁻¹for Y(C₂H₂), 45603(5) cm⁻¹for Y(C₂H₄) and 43475(5) cm⁻¹for Y(C₄H₆). The metal-ligand stretching frequencies of the three complexes are also measured from the MATI spectra.

Using PH₃ as a reactant gas and ruthenium as the target metal in the UNB laser ablation spectrometer, the ruthenium monophosphide molecule (RuP) has been detected. Dispersed fluorescence experiments have been performed to determine ground state vibrational frequencies and the presence of any low-lying electronic states. Rotationally resolved spectra of two vibrational bands at 577nm and 592nm have been taken; the bands have been identified as 1-0 and 0-0 bands based on isotopic shifts. Ruthenium has seven stable isotopes and rotational transitions have been observed for six of the RuP isotopologues. RuP is isoelectronic to RuN so it is expected that RuP will have a ²Σ⁺ ground state and low resolution spectra indicated a likely ²Σ⁺ - ²Σ⁺ electronic transition. Further investigation has led us to believe we are observing a ²Π - ²Σ⁺ transition but mysteriously some important rotational branches are missing. It is hoped that new data to be recorded on a second electronic system we have observed at 535nm will help shed light on this mystery.

Iridium monochloride (IrCl) molecules have been produced in the gas phase using laser ablation sources at the University of New Brunswick (UNB) and Arizona State University (ASU). Low resolution laser induced fluorescence (LIF) spectra, obtained at UNB using a pulsed dye laser, showed three bands at 557, 545 and 534 nm which appeared to form an upper state vibrational progression. Dispersed fluorescence (DF) spectra, obtained by exciting each band at its band head frequency, showed a ground state vibrational progression extending from v=0 to 6. High resolution spectra (FWHM=0.006 cm⁻¹), taken using a cw ring dye laser, showed resolved rotational lines, broadened by unresolved Ir (I=3/2) hyperfine structure, in both the ¹⁹³Ir³⁵Cl and ¹⁹¹Ir³⁵Cl isotopologues. Vibrational assignments of 0-0, 1-0 and 2-0 for the three bands were determined from the isotope structure and the rotational analysis showed the transition to be ³Φ₄ - ³Φ₄, similar to that previously observed in IrF. Higher resolution spectra (FWHM=0.001 cm⁻¹) of the 1-0 band, obtained at ASU, showed resolved hyperfine structure from which the magnetic and quadrupole hyperfine parameters in the ground and excited states were determined. The interpretation of the hyperfine parameters in terms of the electron configurations will be presented along with a comparison of the properties of IrCl and IrF.

The group IIA metals have stable hypermetallic oxides of the general form MOM. Theoretical interest in these species is associated with the multi-reference character of the ground states. It is now established that the ground states can be formally assigned to the M⁺O²⁻M⁺ configuration, which leaves two electrons in orbitals that are primarily metal-centered ns orbitals. Hence the MOM species are diradicals with very small energy spacings between the lowest energy singlet and triplet states. Previously, we have characterized the lowest energy singlet transition (¹Σ⁺_u← X¹Σ⁺_g) of BeOBe. In this study we obtained the first electronic spectrum of CaOCa. Jet-cooled laser induced fluorescence spectra were recorded for multiple bands that occured within the 14,800 - 15,900 cm⁻¹ region. Most of the bands exhibited simple P/R branch rotational line patterns that were blue-shaded. Only even rotational levels were observed, consistent with the expected X ¹Σ⁺_g symmetry of the ground state (⁴⁰Ca has zero nuclear spin). A progression of excited bending modes was evident in the spectrum, indicating that the transition is to an upper state that has a bent equilibrium geometry. Molecular constants were extracted from the rovibronic bands using PGOPHER. The experimental results and interpretation of the spectrum, which was guided by the predictions of electronic structure calculation, will be presented.

ScC molecules have been observed by laser-induced fluorescence, following the reaction of laser-ablated scandium metal with acetylene under supersonic jet-cooled conditions. Rotational analyses have been carried out for about 40 bands of Sc¹²C and Sc¹³C in the region 14000 - 16000 cm⁻¹. Two lower states are found, with Ω = 3/2 and 5/2, indicating that the ground state is ⁴Π_i or ²∆. As yet we cannot distinguish between these alternatives, but note that the ground state of the isoelectronic YC moleculeB. Simard, P.A. Hackett and W.J. Balfour, Chem. Phys. Lett., 230, 103 (1994).s ⁴Π_i. The ground state bond length in ScC is 1.95₅ Å, and the vibrational frequency is 712 cm⁻¹. At least eight electronic transitions occur in the region studied, the majority obeying the selection rule ∆Ω = +1. Rotational perturbations are widespread, consistent with a high density of excited electronic states.

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Footnotes:

B. Simard, P.A. Hackett and W.J. Balfour, Chem. Phys. Lett., 230, 103 (1994).i

Electronic transition spectrum of the tantalum monoflouride (TaF) molecule in the spectral region between 448 and 520 nm has been studied using the technique of laser-ablation/reaction free jet expansion and laser induced fluorescence spectroscopy. TaF molecule was produced by reacting laser-ablated tantalum atoms with sulfur hexafluoride gas seeded in argon. Sixteen vibrational bands with resolved rotational structure have been recorded and analyzed, which were organized into six electronic transition systems and the ground state has been identified to be the X³Σ⁻(0⁺) state with bond length, r_o, and equilibrium vibrational frequency, ω_e, determined to be 1.8209 Å and 700.1 cm⁻¹respectively. In addition, four vibrational bands belong to another transition system involving lower state with Ω = 2 component has also been analyzed. All observed transitions are with ∆Ω = 0. Least-squares fit of the measured line positions yielded molecular constants for the electronic states involved. The Λ-S and Ω states of TaF were calculated at the state-averaged complete active space self-consistent field (SA-CASSCF) and the subsequent internally contracted multi-reference configuration interaction with singles and doubles and Davidson's cluster correction (MRCISD+Q) levels of theory with the active space of 4 electrons in 6 orbitals, that is, the molecular orbitals corresponding to Ta 5d6s are active. The spin-orbit coupling (SOC) is calculated by the state-interaction approach at the SA-CASSCF level via the relativistic effective core potentials (RECPs) spin-orbit operator, where the diagonal elements of the spin-orbit matrix are replaced by the above MRCISD+Q energies. The spectroscopic properties of the ground and many low-lying electronic states of the TaF molecule will be reported. With respect to the observed electronic states in this work, the calculated results are in good agreement with our experimental determinations. This work represents the first experimental investigation of the molecular structure of the TaF molecule.

Despite the irreplaceable role experimental data plays for evaluating the performance of computational predictions, diatomic actinide species have not received much spectroscopic attention. As an early actinide element, thorium-containing species are ideal candidates for these types of studies. The electronic structure is expected to be relatively simple compared to later actinides, and therefore allows straightforward assessment of calculations. Here, we have studied ThCl⁺ for the first time via resonant two-photon ionization of jet-cooled ThCl produced by laser ablation of the metal reacted with dilute Cl₂. Laser-induced Fluorescence (LIF) spectra have been recorded for the neutral molecule from 16000 - 23500 cm⁻¹ in search of a suitable intermediate state for subsequent two-photon ionization experiments. Monochromator dispersion of the fluorescence has recovered the ground state vibration and anharmonic constants of ThCl. Resonant Two-Photon Ionization (R2PI) within a time-of-flight mass spectrometer was used to confirm ThCl production, and Pulsed Field Ionization Zero Kinetic Energy photoelectron spectroscopy (PFI-ZEKE) has been performed to identify the ionization energy as well as several of the low-lying states of the ThCl⁺ molecule. These constants have been predicted at the CASPT2 and CCSD(T) levels of theory, and a discussion of the calculations' performance will be presented alongside the recorded spectra.