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← ¹Σ⁺_g) of BeOBe. Preliminary data for the first electronic transition of the isovalent species, CaOCa, was presented previously (71^st ISMS, talk RI10). We now report the first electronic spectrum of MgOMg. Jet-cooled laser induced fluorescence spectra were recorded for multiple bands that occurred within the 21,000 - 24,000 cm⁻¹ range. 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 (²⁴Mg has zero nuclear spin). 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.

Heavy polar molecules have been used for some time in experiments designed to measure the permanent molecular electric dipole moment, EDM, that is induced by the electron electric dipole moment, eEDM. More recently, ¹⁸¹TaN has been proposedV.V. Flambaum, D. DeMille, M.G. Kozlov, Phys Rev Lett 113 (2014) 103003.s a prime candidate for experiments to measure the EDM induced by the magnetic quadrupole moment, MQM, of the nucleus. There have been a number of calculations to predict these quantities and hyperfine structure parameters are useful indicators of the quality of the electronic wavefunctions used in these calculations with the low-lying a³∆₁ state being of particular interestV.Skripnikov, A.N. Petrov, N.S. Mosyagin, A.V. Titov, V.V. Flambaum, Phys. Rev. A: At., Mol., Opt. Phys. 92 (2015) 012521/1.T. Fleig, M.K. Nayak, M.G. Kozlov, Physical Review A 93 (2016) 012505.. High resolution Laser Induced Fluorescence (LIF) spectra of the of the 0-0 band of the [15.45]0 – a³∆₁ transition of TaN have been obtained using the laser ablation source at Arizona State University. Tantalum hyperfine structure was completely resolved and magnetic and quadrupole hyperfine parameters were determined and, where available, have been compared with predicted values. Calculations of the molecular hyperfine constants using atomic hyperfine parameters have been used to determine the nature and configurations of the electronic states.

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Footnotes:

V.V. Flambaum, D. DeMille, M.G. Kozlov, Phys Rev Lett 113 (2014) 103003.a V.Skripnikov, A.N. Petrov, N.S. Mosyagin, A.V. Titov, V.V. Flambaum, Phys. Rev. A: At., Mol., Opt. Phys. 92 (2015) 012521/1.

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Footnotes:

Electronic transition spectrum of the tungsten monosulfide (WS) molecule in the near infrared region between 725 nm and 885 nm has been recorded using laser ablation/reaction free-jet expansion and laser induced fluorescence spectroscopy. The WS molecule was produced by reacting laser - ablated tungsten atoms with 1% CS₂ seeded in argon. Fifteen vibrational bands with resolved rotational structure have been recorded and analyzed, which were organized into seven electronic transition systems. The ground state has been identified to be the X³Σ⁻(0⁺) state, and the determined vibrational frequency, ∆G_1/2 and bond length, r₀, are respectively 556.7 cm⁻¹ and 2.0676 Å. In addition, vibrational bands belong to another transition system involving lower state with Ω = 1 component have also been analyzed. Least-squares fit of the measured line positions yielded molecular constants for the electronic states involved. The low-lying Λ-S states and Ω sub-states of WS have been calculated using state-averaged complete active space self-consistent field (SA-CASSCF) and followed by MRCISD+Q (internally contracted multi-reference configuration interaction with singles and doubles plus Davidson’s cluster correction). The active space consists of 10 electrons in 9 orbitals corresponding to the W 5d6s and S 3p shells. The lower molecular orbitals from W 5s5p and S 3s are inactive but are also correlated, and relativistic effective core potential (RECPs) are adopted to replace the core orbitals with 60 (W) and 10 (S) core electrons, respectively. Spin-orbit coupling (SOC) is calculated via the state-interaction (SI) approach with RECP spin-orbit operators using SA-CASSCF wavefunctions, where the diagonal elements in the SOC matrix are replaced by the corresponding MRCISD+Q energies calculated above. Spectroscopic constants and potential energy curves of the ground and many low-lying Λ-S states and Ω sub-states of the WS molecule are obtained. The calculated spectroscopic constants of the ground and low-lying states are generally in good agreement with our experimental determination. This work represents the first experimental investigation of the electronic and molecular structure of the WS molecule.

The copper dimer is one of the most studied transition metal (TM) diatomics due to its alkali-metal like electronic shell structure, strongly bound ground state and chemical reactivity. The high electronic promotion energy in the copper atom yields numerous low-lying electronic states compared to TM dimers with (d)-hole electronic configurations. Thus, through extensive study the excited electronic structure of Cu₂ is relatively well known, however in practice few excited states have been investigated with rotational resolution or even assigned term symbols or dissociation limits. The spectroscopic methods that have been used to investigate the copper dimer until now have not possessed sufficient spectral selectivity, which has complicated the analysis of the often overlapping transitions. Resonant four-wave mixing is a non-linear absorption based spectroscopic method. In favorable cases, the two-color version (TC-RFWM) enables purely optical mass selective spectral measurements in a mixed molecular beam. Additionally, by labelling individual rotational levels in the common intermediate state the spectra are dramatically simplified. In this work, we report on the rotationally resolved characterization of low-lying electronic states of dicopper. Several term symbols have been assigned unambiguously. De-perturbation studies performed shed light on the complex electronic structure of the molecule. Furthermore, a new low-lying electronic state of Cu₂ is discovered and has important implications for the high-level theoretical structure calculations performed in parallel. In fact, the ab initio methods applied yield relative energies among the electronic levels that are almost quantitative and allow assignment of the newly observed state that is governed by spin-orbit interacting levels.

Extensive wavelength-resolved fluorescence studies have been carried out for the electronic bands of ScC and Sc¹³C lying in the range 14000 - 16000 cm⁻¹. Taken together with detailed rotational analyses of these bands, these studies have clarified the natures of the low-lying electronic states. The ground state is an Ω = 3/2 state, with a vibrational frequency of 648 cm⁻¹, and the first excited electronic state is an Ω = 5/2 state, with a frequency of 712 cm⁻¹, lying 155.54 cm⁻¹ higher. These states are assigned as the lowest spin-orbit components of X²Π_i and a⁴Π_i, respectively. The quartet nature of the a state is confirmed by the observation of the ⁴Π_3/2 component, 18.71 cm⁻¹ above the ⁴Π_5/2 component. The strongest bands in the region studied are two ⁴∆_7/2 - ⁴Π_5/2 transitions, where the upper states lie 14355 and 15445 cm⁻¹ above X²Π_3/2. Extensive doublet-quartet mixing occurs, which results in some complicated emission patterns. The energy order, a⁴Π above X²Π, is consistent with the ab initio calculations of Kalemos et al., A. Kalemos, A. Mavridis and J.F. Harrison, J. Phys. Chem. A155, 755 (2001).ut differs from that found by Simard et al in the isoelectronic YC molecule.B. Simard, P.A. Hackett and W.J. Balfour, Chem. Phys. Lett., 230, 103 (1994).html:<hr /><h3>Footnotes: A. Kalemos, A. Mavridis and J.F. Harrison, J. Phys. Chem. A155, 755 (2001).b B. Simard, P.A. Hackett and W.J. Balfour, Chem. Phys. Lett., 230, 103 (1994).

Cerium oxides are widely used in heterogeneous catalysis due to their ability to switch between different oxidation states. We report here the mass-analyzed threshold ionization (MATI) spectroscopy of cerium monoxide (CeO) produced by laser ablating a Ce rod in a molecular beam source. The MATI spectrum in the range of 40000-45000 cm⁻¹exhibits several band systems with similar vibrational progressions. The strongest band is at 43015 (5) cm⁻¹, which can be assigned as the adiabatic ionization energy of the neutral species. The spectrum also shows Ce-O stretching frequencies of 817 and 890 cm⁻¹in the neutral and ion states, respectively. By comparing with spin-orbit coupled multireference quasi-degenerate perturbation theory (SO-MCQDPT) calculations, the observed band systems are assigned to transitions from various low-energy spin-orbit levels of the neutral oxide to the two lowest spin-orbit levels of the corresponding ion. The current work will also be compared with previous experimental and computational studies on the neutral species.

The spin-forbidden a ⁴Σ⁻ - X ²Π_r transition of germanium hydride, GeH, was reported in emission in 1953 by Kleman and Werhagen. In our study, Intracavity Laser Spectroscopy, ILS, was used to obtain the first high resolution spectrum of this transition between 15,000 cm⁻¹and 16,500 cm⁻¹. The GeH molecules were produced in the plasma discharge of an Al-plate electrode, using  800 mTorr H₂ and  600 mTorr of GeH₄. The plasma was formed within the cavity of a tunable dye laser system, and the molecular absorption features are enhanced during an initial generation time prior to detection. The cathode length was 150 mm, the laser cavity was 1.15 m long, and a generation time of 180 μsec was used, resulting in an effective pathlength of  7 km. The spectra were collected intermittently with those from an external I₂ cell, and the spectra were calibrated using PGOHPER and the Doppler-limited I₂ spectrum of Salami and Ross. The obtained line positions were fit using PGOPHER. Results of the analysis will be presented.

The red band of CuO has been observed at high resolution using Intracavity Laser Spectroscopy (ILS). The red band was rotationally analyzed in 1974 by Appelblad and Lagerqvist and a portion of the band structure was assigned as the spectrum of the [16.5] A ²Σ⁺ - X ²Π_i transition. Subsequent analyses of CuO showed that the character of the A state was ²Σ⁻ in character, and thus the Λ-doubling parameter, p, was inverted, and the e/f parity assignments were reversed. In this study, the spectrum of CuO was recorded in the in the regions 16,150 cm⁻¹– 16,270 cm⁻¹and 16,405 cm⁻¹- 16,545 cm⁻¹. The CuO molecules were produced in the plasma discharge of a copper hollow cathode within the cavity of a tunable dye laser, using 0.6 torr of argon as the sputter gas and a trace amount of O₂ as the source of oxygen. The plasma spectra were recorded intermittently with spectra from an external I₂ cell, and line positions from the widely used Iodine Atlas were used for calibration. In uncongested regions of the spectrum, both ⁶³CuO and ⁶⁵CuO were observed with appreciable intensity. The resulting spectra were rotationally analyzed for both isotopologues, fitting the data as a ²Σ⁻ - ²Π_i transition using PGOPHER. Line positions from the millimeter wave and FTIR studies of ⁶³CuO performed in the late 1990s were included in the fit to overcome potential complications due to the ambiguous parity assignments prevalent in the CuO literature. Previously unreported molecular constants were obtained from the fit for ⁶⁵CuO, and the constants of ⁶³CuO are determined to at least an order of magnitude greater than the results of Appelblad and Lagerqvist. Results of this analysis will be presented.

Four new electronic transitions with blue-degraded bandheads were observed in the orange-red region of the visible spectrum. The transitions were observed in the plasma discharge of a hollow copper cathode placed within the cavity of a tunable dye laser system, allowing molecular absorbance to be enhanced upon laser amplification. To produce the molecules, the surface of the copper cathode was soaked in a dilute ammonia solution prior to installation, and 1 torr of H₂ was used as the sputter gas in the dc plasma discharge. The bandheads were observed at 16,560 cm⁻¹, 16,485 cm⁻¹, 16,027 cm⁻¹, and 15,960 cm⁻¹. Using 1.5 torr of D₂ as the sputter gas resulted in a -3 cm⁻¹shift in origin for the bands in the  16,000 cm⁻¹region. Four rotational branches have been identified in each transition, and the transitions have been fit to independent ²Σ - ²Π transitions using PGOPHER, with spin-orbit splittings in the Hund’s case (a) Π-states of -71.2 cm⁻¹and -65.4 cm⁻¹. The transitions have tentatively been assigned to HCuN. Results of this analysis will be presented.

The pure rotational spectrum of potassium monoxide (KO) has been recorded using millimeter-wave direct absorption spectroscopy. KO was synthesized by the reaction of potassium vapor, produced in a Broida-type oven, with nitrous oxide. No DC discharge was necessary. Eleven rotational transitions belonging to the ²Π_3/2 spin-orbit component have been measured and have been fit successfully to a case (c) Hamiltonian. Rotational and lambda-doubling constants for this spin-orbit component have been determined. It has been suggested that the ground electronic state of KO is either ²Π (as for LiO and NaO) or ²Σ (as for RbO and CsO), both of which lie close in energy. Recent computational studies favor a ²Σ ground state. Further measurements of the rotational transitions of the ²Π_1/2 spin-orbit component and the ²Σ state are currently in progress, as well as the potassium hyperfine structure.