Two laser-induced fluorescence techniques were used to access the high-lying C²Π state (41242 cm⁻¹) in the metal-bearing molecule MgH. First, we directly excited the C²Π state from the X²Σ⁺ ground state with UV light produced by frequency-doubling pulsed visible laser light. Second, a resonant two-photon experiment was performed with different laser beams tuned to the A²Π - X²Σ⁺ and C²Π - A²Π transitions. Term energies for levels up to J = 11.5 were fit to a ²Π Hamiltonian to yield rotational parameters B = 6.1045(10) cm⁻¹, D = 3.176(86)×10⁻⁴ cm⁻¹, A = 3.843(60) cm⁻¹, and p = -2.653(88) ×10⁻² cm⁻¹. We also observed levels of a ²∆ state (42192 cm⁻¹) up to J = 4.5 with the two-photon technique. Guntch previously observed the ²∆ - A²Π spectrum in 1937, but assigned the upper state as ²Σ⁻. The molecular parameters determined for the ²∆ state are B = 6.2861(23) cm⁻¹and A = -0.168(17) cm⁻¹.

Accurate studies of the ground and low lying excited triplet pi-states of the covalently bonded alkaline earth metal carbides have been of interest to both theoreticians and experimentalists in the past few decades to understand their bonding. Diatomic beryllium carbide (BeC), which is valence iso-electronic with MgC, was probed by laser ablation and jet cooling techniques producing rotationally resolved data reported in a previous study.[1] Dynamically weighted MRCI calculations were used to construct adiabatic potential energy curves for the ground and the four lowest triplet pi-states up to 50,000 cm⁻¹. From these, diabatic potentials and couplings were obtained and used to compute vibronic levels for the four interacting states. Here we apply the same methodology to MgC and examine the similarities and differences between the two systems. Results show significantly different bonding characteristics for the pi-states of MgC when compared to BeC. References: 1- B. J. Barker et al. J. Chem. Phys. 137, 214313 (2012).

The electronic transition spectrum of scandium monoxide (ScO) in the spectral region between 290 and 311 nm has been recorded using laser ablation/reaction free-jet expansion and laser induced fluorescence spectroscopy. The ScO molecule was produced by reacting laser-ablated yttrium atoms with O₂ gas seeded in argon. Twenty transition bands were observed and thirteen of them have been selected for further studied by optical-optical double resonance (OODR) spectroscopy. Higher-lying electronic excited states have been reached via the intermediate B² Σ⁺ state from the ground X² Σ⁺ state. Our analysis indicates that the upper states conform to Hund’s case (c) coupling scheme, the sub-states analyzed so far have Ω = 0.5 and 1.5. In addition, for the first time, a quartet state namely ⁴ Σ⁺ state has been identified experimentally. Least squares fits of the measured rotational lines yield molecular constants for the newly identified excited states.

The electronic transition spectrum of scandium monophosphide (ScP) molecule in the visible region between 480 nm and 550 nm has been recorded and analyzed using laser ablation/reaction free-jet expansion and laser induced fluorescence spectroscopy. The ScP molecule was produced by reacting laser - ablated scandium atoms with PH₃ seeded in argon. Ten vibrational bands were recorded and they are identified to be belonging to three electronic transition systems, namely the [19.1]¹ Π₁ - X¹ Σ transition, [19.5]¹ Σ - X¹ Σ transition, and [19.8] ³ Π_i - X³ Π_i transition. ScP has been determined to have a X¹ Σ ground state in our earlier work. A least squares fit of the measured rotational lines yielded molecular constants for the single and the triplet electronic states. Theoretical calculation results have been used to help the assignment of the observed electronic states.

The (0,0) band of the A²Π_3/2 - X²Σ⁺ transition of ZrN is known to be perturbed. Both homogeneous and heterogeneous perturbations are observed in the spectrum. A recent high-level ab initio calculation has helped to identify several possible perturbing states. PGOPHER is used to analyze the interactions. ZrN was produced in a hollow cathode sputter source, and the spectrum was recorded in emission by a high resolution FT spectrometer. Results of the analysis will be presented.

A new electronic transition of molybdenum monoxide, MoO, was observed near 6735 cm⁻¹. Based upon recent ab initio calculations, the transition is tentatively assigned as the (0,0) band of the c³Π – b³Σ⁻ transition. PGOPHER was used to analyze the line positions observed in the spectrum. MoO molecules were produced in a Mo-lined hollow cathode sputter source, and the spectrum was recorded in emission using the high resolution spectrometer associated with the McMath-Pierce Solar telescope at Kitt Peak, AZ. Results of the analysis will be presented.

The first spectroscopic study of rhenium carbide, ReC, has been performed using both low and high resolution techniques to collect rotationally resolved electronic spectra from 420 to 500nm. Laser-induced fluorescence (LIF), and dispersed fluorescence (DF) techniques were employed. ReC was formed in our laser ablation molecular jet apparatus by ablating a rhenium target rod in the presence of 1% methane in helium. The low resolution spectrum identified four bands of an electronic system belonging to ReC, three of which have been studied so far. Extensive hyperfine structure composed of six hyperfine components was observed in the high resolution spectrum, as well as a clear distinction between the ¹⁸⁷ReC and ¹⁸⁵ReC isotopologues. The data seems consistent with a ⁴Π - ⁴Σ⁻ transition, as was predicted before experimentation¹.Dispersed fluorescence spectra allowed us to determine the ground state vibrational frequency (ω_e^′′=994.4 ± 0.3 cm⁻¹), and to identify a low-lying electronically excited state at T_e^′′=1118.4 ± 0.4 cm⁻¹with a vibrational frequency of ω_e^′′=984 ± 2 cm⁻¹.
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¹Personal communication, F. Grein, University of New Brunswick

A new electronic transition of PtF was observed by intracavity laser absorption spectroscopy. Based on the theoretical calculations of the electronic structure, this spectrum is assigned as the ²Σ⁺ - ²Σ⁺ transition. PtF molecules were produced in a Pt-lined hollow cathode sputter source in Ar with a trace of SF₆. Results of the analysis will be presented.

The bonding and electrostatic properties of gold containing molecules are highly influenced by relativistic effects and electron correlation ¹. Hence it is difficult to predict those properties via electron structure calculation, and such calculation are guided by experimental observations. Here we report on the A(Ω = 1)−X¹Σ⁺ and B(Ω = 0)−X¹Σ⁺ bands of AuCl, which have been previously recorded at Doppler limited resolution ². A cold molecular beam sample was generated and the bands were recorded at high resolution (FWHM =35 MHz) using laser excitation spectroscopy, both field-free and in the presence of a static electric field. An improved set of spectroscopic parameters for the A(Ω = 1) and B(Ω = 0) states were obtained. The Stark induced shifts were analyzed to determine the permanent electric dipole moments for the X, A, and B states. A comparison with AuF ³ and theory will be made.
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¹P. Pyykko; Angew Chem. Int 43 4412, 2004. ²L. C. O’Brien, A. L. Elliott, and M. Dulick; J. Mol. Spectrosc 194 124, 1999. ³T. C. Steimle, R. Zhang, C. Qin and T. D. Varberg; J. Phys. Chem. A 117(46) 11739,2013.

Lanthanum hydride (LaH) molecules were produced in a pulsed supersonic molecular beam by reaction of laser produced lanthanum metal plasma with  ∼ 2% ammonia seeded in helium gas. Rotationally resolved laser-induced fluorescence excitation bands involving two excited electronic states, originating from ν=0 of ground state X¹Σ⁺ were observed with band origins at 21970.71(1) and 22100.31(3) cm⁻¹. Rotational analysis confirmed these transitions as Ω=0⁺- X¹Σ⁺. The rotational lines up to J^"=6 were observed in the 21970.71 cm⁻¹ band. However, for the 22100.31 cm⁻¹ band, rotational lines up to J^"=12 in the P-branch and J^"up to 10 in the R-branch was observed. The molecular constants for both the excited states were determined by fitting rotational line wavenumbers to an effective Hamiltonian operator for Ω=0⁺ and X¹Σ⁺ state using the Pgopher program.

Gaseous was prepared in a high temperature furnace, and rotational spectra were measured in the 500-550 GHz and 590-650 GHz ranges. Transitions with J from 24 to 32 were observed in the Ω = 4 ground state and low lying vibronic states with Ω = 3 to Ω = 5. Spectra were modeled using Dunham theory for diatomic molecules.

Figure Determining the physical properties (bond lengths, angles, dipole moments, etc) of transition metal oxides and dioxides is relevant to catalysis, high temperature chemistry, materials science and astrophysics. Analysis of optical spectra is a convenient method for extraction of physical properties, but can be difficult because of the density of electronic states and in the case of the dioxides, presence of both the oxide and superoxide forms. Here we demonstrate the application of two dimensional fluorescence spectroscopy¹ for aiding in the assignment and analysis. Particular attention will be paid to the spectroscopy of first row transition metal monoxides and dioxides of Nickel, NiO and NiO₂, and Manganese, MnO. Furthermore, the application of this technique to discovering the spectrum of other transition metal systems such as Metal-dicarbides will be outlined.
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¹N.J. Reilly, T.W. Schmidt, S.H. Kable, J. Phys. Chem. A., 110(45), 12355-12359, 2006

High resolution infrared emission spectra of hot MgF₂ in the 700 to 1300 cm⁻¹ region have been recorded. The molecules were generated by heating solid MgF₂ to 1675 ^°C. Four vibrational bands were rotationally analyzed yielding band origins and rotational constants. Observed bands are: 001-000 (Σ_u⁺ - Σ_g⁺), 01¹1 – 01¹0 (Π_g – Π_u), 02²1 (f parity) – 02²0 (f parity) (∆_u – ∆_g), and 03³1 – 03³0 (Φ_g – Φ_u). High level ab initio calculations were essential in making assignments and in helping to fit the data. The ∆_u – ∆_g band was only observed for f-parity because the e-parity is significantly perturbed by l-resonance.

A rod of depleted uranium metal (mp = 1,132^° C) has been ablated with the fundamental operating frequency of a Nd:YAG laser. The resulting ablation plume of uranium was then mixed with argon gas and expanded between the transmit/receive horn antennae of a chirp-pulse Fourier transform microwave spectrometer. The recorded spectra show nine strong transitions which are not present when the laser is not used in the experimental procedure. A series of experiments in which the backing gas conditions were altered provides evidence that the nine observed transitions are carried by the same species. Should the transitions be from one species it is most likely an asymmetric top. The transitions persist even when ultra-pure argon is used as the sole backing gas. The oxide coating of the uranium metal likely provides a source of oxygen and, presently, the "top" candidate for the unknown molecule is UO₃, which is known to have C₂v symmetry. Double resonance experiments are planned to aid transition assignments. A plausible explanation for an elusive assignment to date is the presence of pseudo-rotation.

We report mass spectra, 488 nm anion photoelectron spectra, and density functional theory (DFT) calculations of organometallic complexes produced by flow tube reactions of niobium with butadiene (C₄H₆), and compare these results with those obtained upon reactions with ethylene (C₂H₄). In the C₄H₆ experiments, NbC₄H₄⁻ is the most abundant product anion, indicating loss of H₂ upon reaction with Nb. DFT analysis of the vibrationally-resolved photoelectron spectrum indicates that the ³A′ anion incorporates a five-membered Nb-C₄ ring in which the Nb atom lies outside the C₄ plane. The electron affinity of the corresponding neutral molecule (²A′) is measured to be 0.997 ± 0.006 eV. Upon reaction with C₂H₄, at least one additional isomer of NbC₄H₄⁻ is produced, giving rise to broad spectral features at higher electron binding energies. Reactions with C₄H₆ also yield relatively small amounts of the NbC₆H₆⁻ and NbC₆H₄⁻ product anions, indicating C-C bond activation in addition to dehydrogenation. The former anion displays the ³A₁, C_6v Nb-benzene π-complex structure previously observed upon reaction with C₂H₄. The NbC₆H₄⁻ anion produced upon reaction with C₄H₆ yields at least two vibrationally-resolved photodetachment transitions. DFT calculations performed to date suggest that the lower electron binding energy transition, which indicates an electron affinity of 1.110 ± 0.008 eV for the corresponding neutral complex, is due to the ⁴B₂ ← ³B₂ detachment from a planar, C_2v Nb-benzyne anion.

Ab initio calculations were employed to investigate M⁺—RG₂ species. Trends in binding energies, D_e, bond lengths, and bond angles are discussed and rationalised by analysing the electronic wavefunction. Mulliken, natural population, and atoms-in-molecules (AIM) population analyses are performed. It is found that some complexes are linear whereas others are bent. Those results are discussed in terms of hybridization and the various interactions present in these species. The work is a continuation from a previously published study¹ where Group 2 Be⁺—RG₂ and Mg⁺—RG₂ species are investigated and compared with Group 1 Li⁺—RG₂ and Na⁺—RG₂ species.
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¹A. Andrejeva, A. M. Gardner, J. B. Graneek, R. J. Plowright, W. H. Breckenridge and T. G. Wright, J. Phys. Chem. A., 117, 13578 (2013)