High resolution electronic spectroscopy of uranium mononitride, UN.

The isoelectronic molecules UN and UO+ are known to have Ω = 3.5 and Ω = 4.5 ground states, respectively (where Ω is the unsigned projection of the electronic angular momentum along the internuclear axis). A ligand field theory model has been proposed to account for the difference [Matthew and Morse, J. Chem. Phys. 138, 184303 (2013)]. The ground state of UO+ arises from the U3+(5f3(4I4.5))O2- configuration. Owing to the higher nominal charge of the N3- ligand, the U3+ ion in UN is stabilized by promoting one of the 5f electrons to the more polarizable 7s orbital, reducing the repulsive interaction with the ligand and rendering U3+(5f27s(4H3.5))N3- the lowest energy configuration. In the present work, we have advanced the characterization of the UN ground state through studies of two electronic transitions, [18.35]4.5-X(1)3.5 and [18.63]4.5-X(1)3.5, using sub-Doppler laser excitation techniques with fluorescence detection. Spectra were recorded under field-free conditions and in the presence of static electric or magnetic fields. The ground state electric dipole moment [µ = 4.30(2) D] and magnetic ge-factor [2.160(9)] were determined from these data. These values were both consistent with the 5f27s configurational assignment. Dispersed fluorescence measurements were used to determine vibrational constants for the ground and first electronically excited states. Electric dipole moments and magnetic ge-factors are also reported for the higher-energy electronically excited states.

Electronic Configuration Assignments for UO from Electric Dipole Moment Measurements.

Diatomic UO has more than 48 bound states within 10000 cm-1 of the ground state. This electronic state congestion has been attributed to interleaved states from the electronic configurations U2+(5f37s)O2- and U2+(5f27s2)O2-, respectively. Ligand field theory predicts that each electronic configuration will exhibit states with distinguishable, characteristic vibrational and rotational constants. However, vibronic state mixing modifies the observed vibration-rotation constants, leading to uncertainty in the configurational assignments. The permanent electric dipole moment (µe) of an electronic state should also manifest a value that is characteristic of the parent electronic configuration. µe and other electrostatic and magnetostatic properties should be less influenced by the vibronic state mixing, providing more robust indicators for configurational assignments. In the present study, we have measured the µe values for four electronic states of UO. The results clearly demonstrate that the ground state (X(1)4) and the first electronically excited state ((2)4) are derived from the U2+(5f37s)O2- and U2+(5f27s2)O2- configurations, respectively.

Electronic Spectroscopy of SmO in the 645 to 670 nm Range.

The associative ionization reaction Sm + O → SmO+ + e- is being investigated as an electron source that could transiently modify high-altitude electron densities via Sm vapor release. Electronic spectra have been obtained from tests where sounding rockets released Sm vapor, but the interpretation of these results has been hampered by the limited laboratory spectral data available for both SmO and SmO+. The present study extends the spectroscopic characterization of SmO in the 645-670 nm range, where the field data show the most prominent molecular emission features. Rotationally resolved excitation spectra, dispersed laser-induced fluorescence spectra, and fluorescence decay lifetimes are reported. The results are consistent with the assignment of a subset of the red-region bands to configurational transitions of the form Sm2+(4f56s)O2- ↔ Sm2+(4f55d)O2-. Analysis of the excited state hyperfine structure supports this configurational description.

Fine and hyperfine interactions in 171YbOH and 173YbOH.

The odd isotopologues of ytterbium monohydroxide, 171,173YbOH, have been identified as promising molecules to measure parity (P) and time reversal (T) violating physics. Here, we characterize the Ã2Π1/2(0,0,0)-X̃2Σ+(0,0,0) band near 577 nm for these odd isotopologues. Both laser-induced fluorescence excitation spectra of a supersonic molecular beam sample and absorption spectra of a cryogenic buffer-gas cooled sample were recorded. In addition, a novel spectroscopic technique based on laser-enhanced chemical reactions is demonstrated and used in absorption measurements. This technique is especially powerful for disentangling congested spectra. An effective Hamiltonian model is used to extract the fine and hyperfine parameters for the Ã2Π1/2(0,0,0) and X̃2Σ+(0,0,0) states. A comparison of the determined X̃2Σ+(0,0,0) hyperfine parameters with recently predicted values [Denis et al., J. Chem. Phys. 152, 084303 (2020); K. Gaul and R. Berger, Phys. Rev. A 101, 012508 (2020); and Liu et al., J. Chem. Phys. 154,064110 (2021)] is made. The measured hyperfine parameters provide experimental confirmation of the computational methods used to compute the P,T-violating coupling constants Wd and WM, which correlate P,T-violating physics to P,T-violating energy shifts in the molecule. The dependence of the fine and hyperfine parameters of the Ã2Π1/2(0,0,0) and X̃2Σ+(0,0,0) states for all isotopologues of YbOH are discussed, and a comparison to isoelectronic YbF is made.

Branching Ratios, Radiative Lifetimes, and Transition Dipole Moments for YbOH.

Medium resolution (Δν̃ ∼ 3 GHz) laser-induced fluorescence (LIF) excitation spectra of a rotationally cold sample of YbOH in the 17300-17950 cm-1 range have been recorded using two-dimensional (excitation and dispersed fluorescence) spectroscopy. High resolution (Δλ ∼ 0.65 nm) dispersed laser-induced fluorescence (DLIF) spectra and radiative decay curves of numerous bands detected in the medium resolution LIF excitation spectra were recorded. The vibronic energy levels of the X̃2Σ+ state were predicted using a discrete variable representation approach and compared with observations. The radiative decay curves were analyzed to produce fluorescence lifetimes. DLIF spectra resulting from high resolution (Δν̃ < 10 MHz) LIF excitation of individual low-rotational lines in the Ã2Π1/2(0,0,0)-X̃2Σ+(0,0,0), Ã2Π1/2(1,0,0)-X̃2Σ+(0,0,0), and [17.73]Ω = 0.5(0,0,0)-X̃2Σ+(0,0,0) bands were also recorded. The DLIF spectra were analyzed to determine branching ratios which were combined with radiative lifetimes to obtain transition dipole moments. The implications for laser cooling and trapping of YbOH are discussed.

Characterization of gas-phase thorium nitride.

Properties of gas-phase thorium nitride, ThN, have been experimentally determined from a combined optical and microwave spectroscopic study. An intense band near 555 nm has been assigned as the [18.0]1.5-X2Σ+ (0,0) transition and recorded at high resolution in the presence of static electric and magnetic fields. The observed optical Stark shifts were analyzed to determine permanent electric dipole moments, µâ†’el for the [18.0]1.5 and X2Σ+ states of 4.38 ± 0.02D and 5.11 ± 0.09D, respectively. Zeeman shifts were used to determine the magnetic g-factors. The pure rotational spectrum was recorded using a separated field optical pump/probe microwave repopulation scheme and analyzed to determine the bond length and 14N magnetic hyperfine and nuclear electric quadrupole parameters. A molecular orbital correlation diagram and ligand field electronic structure models are used to provide a qualitative interpretation of the electronic state ordering, magneto- and electro-static properties, and hyperfine interactions. Electronic structure calculations for the X2Σ+ state were performed, and results were compared with observations. Observed trends in µâ†’el for the ThX (X = N, S, O, F, and Cl) series are discussed.

The electric dipole moments in the ground states of gold oxide, AuO, and gold sulfide, AuS.

The B2Σ- - X2Π3/2(0,0) bands of a cold molecular beam sample of gold monoxide, AuO, and gold monosulfide, AuS, have been recorded at high resolution both field free and in the presence of a static electric field. The observed electric field induced splittings and shifts were analyzed to produce permanent electric dipole moments, µâ†’el, of 2.94±0.06 D and 2.22±0.05 D for the X2Π3/2(v = 0) states of AuO and AuS, respectively. A molecular orbital correlation diagram is used to rationalize the trend in ground state µâ†’el values for AuX (X = F, Cl, O, and S) molecules. The experimentally determined µâ†’el are compared to those computed at the coupled-cluster singles and doubles (CCSD) level augmented with a perturbative inclusion of triple excitations (CCSD(T)) level of theory.

Au-S Bonding Revealed from the Characterization of Diatomic Gold Sulfide, AuS.

Gold monosulfide, AuS, has been detected and characterized in the gas phase using optical spectroscopy. The symmetries of the ground and low-lying electronic excited states have been determined by application of a synergy of hot and cold laser excitation techniques. The electronic spectra are assigned to progressions in four band systems associated with excitations from the X(2)Πi ((2σ)(2)(2π)(3)) ground state to the A(2)Σ(+) state arising from the (2σ)(1)(2π)(4) configuration and to the a(4)Σ(-), B(2)Σ(-), and C(2)Δi states arising from the (2σ)(2)(2π)(2)(3σ*)(1) configuration. The bond length and dissociation energy of the ground X(2)Πi state are determined to be 2.156(2) Å and 298 ± 2 kJ/mol, respectively. A molecular orbital correlation diagram is used to rationalize the energy ordering of the excited states and the associated harmonic frequencies.

High resolution electronic spectroscopy of the A (2)Σ- - X (2)Π1/2 transition of PtN.

The (2,0) vibrational band of the A (2)Σ(-) - X (2)Π1/2 transition of platinum nitride, PtN, was recorded at Doppler-limited resolution using intracavity laser absorption spectroscopy (ILS) and at sub-Doppler resolution using molecular beam laser induced fluorescence (LIF) spectroscopy. Isotopologue structure for (194)PtN, (195)PtN, and (196)PtN, magnetic hyperfine splitting due to (195)Pt (I = ½), and nuclear quadrupole splitting due to (14)N (I = 1) were observed in the spectrum. Molecular constants for the ground and excited states are derived. The hyperfine interactions are used to illuminate the nature of the A (2)Σ(-) excited electronic state.

The electric dipole moment of magnesium deuteride, MgD.

The (0,0) A(2)Π-X (2)Σ(+) band of a cold molecular beam sample of magnesium monodeuteride, MgD, has been recorded field-free and in the presence of a static electric field of up to 11 kV/cm. The lines associated with the lowest rotational levels are detected for the first time. The field-free spectrum was analyzed to produce an improved set of fine structure parameters for the A(2)Π (v = 0) state. The observed electric field induced splittings and shifts were analyzed to produce permanent electric dipole moments, µ(el) of 2.567(10)D and 1.31(8)D for A(2)Π (v = 0) and X(2)Σ(+)(v = 0) states, respectively. The recommended value for µ(el)(X(2)Σ(+) (v = 0)) for MgH, based upon the measured value for MgD, is 1.32(8)D.

The electric dipole moment of cobalt monoxide, CoO.

A number of low-rotational lines of the E(4)Δ7/2 ← X(4)Δ7/2 (1,0) band system of cobalt monoxide, CoO, were recorded field free and in the presence of a static electric field. The magnetic hyperfine parameter, h7/2, and the electron quadrupole parameter, eQq0, for the E(4)Δ7/2(υ = 1) state were optimized from the analysis of the field-free spectrum. The permanent electric dipole moment, µ(→)(el), for the X(4)Δ7/2 (υ = 0) and E(4)Δ7/2 (υ = 1) states were determined to be 4.18 ± 0.05 D and 3.28 ± 0.05 D, respectively, from the analysis of the observed Stark spectra of F' = 7 ← F″ = 6 branch feature in the Q(7/2) line and the F' = 8 ← F″ = 7 branch feature in the R(7/2) line. The measured dipole moments of CoO are compared to those from theoretical predictions and the trend across the 3d-metal monoxide series discussed.

The permanent electric dipole moment of thorium sulfide, ThS.

Numerous rotational lines of the {18.26}1-X(1)Σ(+) band system of thorium sulfide, ThS, were recorded near 547.6 nm at a resolution of approximately 30 MHz. Measurements were made under field-free conditions, and in the presence of a static electric field. The field-free spectrum was analyzed to produce rotational and Λ-doubling parameters. The Stark shifts induced by the electric field were analyzed to determine permanent electric dipole moments, µâƒ—el, of 4.58(10) D and 6.72(5) D for the X(1)Σ(+) (v = 0) and {18.26}1 states, respectively. The results are compared with the predictions of previous and new electronic structure calculations for ThS, and the properties of isovalent ThO.

The pure rotational spectrum of ruthenium monocarbide, RuC, and relativistic ab initio predictions.

The J = 1 ← J = 0 and J = 2 ← J = 1 rotational transitions of ruthenium monocarbide, RuC, have been recorded using the separated field pump/probe microwave optical double resonance technique and analyzed to determine the fine and hyperfine parameters for the X(1)Σ(+) state. The (101)Ru(I = 5/2) electric quadrupole parameter, eq0Q, and nuclear spin-rotation interaction parameter, C(I)(eff), were determined to be 433.19(8) MHz and -0.049(6) MHz, respectively. The equilibrium bond distance, r(e), was determined to be 1.605485(2) Å. Hartree-Fock and coupled-cluster calculations were carried out for the properties of the X(1)Σ(+) state. Electron-correlation effects are pronounced for all properties studied. It is shown that (a) the moderate scalar-relativistic contribution to eq0Q is entirely due to the coupling between scalar-relativistic and electron-correlation effects, (b) the spin-free exact two-component theory in its one-electron variant offers a reliable and efficient treatment of scalar-relativistic effects, and (c) non-relativistic theory performs quite well for the prediction of C(I)(elec), provided that electron correlation is treated accurately.

Hyperfine interactions and electric dipole moments in the [16.0]1.5(v = 6), [16.0]3.5(v = 7), and X2Δ(5/2) states of iridium monosilicide, IrSi.

The (6,0)[16.0]1.5-X(2)Δ(5/2) and (7,0)[16.0]3.5-X(2)Δ(5/2) bands of IrSi have been recorded using high-resolution laser-induced fluorescence spectroscopy. The field-free spectra of the (191)IrSi and (193)IrSi isotopologues were modeled to generate a set of fine, magnetic hyperfine, and nuclear quadrupole hyperfine parameters for the X(2)Δ(5/2)(v = 0), [16.0]1.5(v = 6), and [16.0]3.5 (v = 7) states. The observed optical Stark shifts for the (193)IrSi and (191)IrSi isotopologues were analyzed to produce the permanent electric dipole moments, µ(el), of -0.414(6) D and 0.782(6) D for the X(2)Δ(5/2) and [16.0]1.5 (v = 6) states, respectively. Properties of the X(2)Δ(5/2) state computed using relativistic coupled-cluster methods clearly indicate that electron correlation plays an essential role. Specifically, inclusion of correlation changes the sign of the dipole moment and is essential for achieving good accuracy for the nuclear quadrupole coupling parameter eQq0.

Molecular-beam optical stark and zeeman study of the [17.8]0+-X1Σ+ (0,0) band system of AuF.

The [17.8]0(+)-X(1)Σ(+) (0,0) band of gold monofluoride, AuF, has been recorded at a resolution of 40 MHz both field free and in the presence of a static electric and magnetic field. The observed Stark shifts were analyzed to determine the permanent electric dipole moment, µel, of 2.03 ± 0.05 D and 4.13 ± 0.02 D, for the [17.8]0(+)(v = 0) and X(1)Σ(+)(v = 0) states, respectively. The small magnetic tuning observed for the [17.8]0(+)(v = 0) state is attributed to rotational and magnetic field mixing with the [17.7]1 state and has been successfully modeled using an effective Hamiltonian for the (3)Π state. A comparison with the numerous published theoretical predictions is made.

The molecular frame electric dipole moment and hyperfine interactions in hafnium fluoride, HfF.

The (1,0) [17.9]2.5-X(2)Δ(3∕2) band of hafnium monofluoride (HfF) has been recorded using high-resolution laser-induced fluorescence spectroscopy both field-free and in the presence of a static electric field. The field-free spectra of (177)HfF, (179)HfF, and (180)HfF were modeled to generate a set of fine and hyperfine parameter for the X(2)Δ(3∕2)(v = 0) and [17.9]2.5 (v = 1) states. The observed optical Stark shifts for the (180)HfF isotopologue were analyzed to produce the molecular frame electric dipole moments of 1.66(1) D and 0.419(7) D for the X(2)Δ(3∕2) and [17.9]2.5 state, respectively. Both the generalized effective core potential and all-electron four component approaches were used in ab initio calculations to predict the properties of ground state HfF including equilibrium distance, dipole moments, quadrupole coupling, and magnetic hyperfine constants.

The permanent electric dipole moment and hyperfine interactions in platinum monofluoride, PtF.

The [11.9]Ω = 3/2 ← X (2)Π(3/2)(0,0) and (1,0) bands of platinum monofluoride, PtF, have been recorded field-free and in the presence of a static electric field. The (19)F(I = 1/2) and (195)Pt(I = 1/2) magnetic hyperfine interactions have been analyzed and compared with predicted values obtained using atomic information and a proposed molecular orbital correlation diagram. The optical Stark shifts were analyzed to produce the permanent electric dipole moments, µ(el), of 2.47(11)D and 3.42(6)D for the [11.9]Ω = 3/2 and X (2)Π(3/2)states, respectively. The observed trend in µ(el) for the PtX (X = C,N,O,S and F) series is discussed and a comparison with IrF made.

Optical Zeeman spectroscopy of the (0,0) B4Γ-X4Φ band systems of titanium monohydride, TiH, and titanium monodeuteride, TiD.

The Zeeman effect in the (0,0) bands of the B(4)Γ(5/2)-X(4)Φ(3/2) system of titanium monohydride, TiH, and titanium monodeuteride, TiD, has been recorded and analyzed. Magnetic tuning of the spectral features recorded at high resolution (full width at half maximum ≅ 35 MHz) and at a field strength of 4.5 kG is accurately modeled using an effective Zeeman Hamiltonian. The determined magnetic g-factors for the X(4)Φ(3/2) (v = 0) state deviate only slightly from those expected for an isolated (4)Φ(3/2) state whereas those for the B(4)Γ(5/2)(v = 0) deviate significantly from those of an isolated (4)Γ(5/2) state. The rotational dependence of the magnetic tuning in the B(4)Γ(5/2)(v = 0) state is attributed to perturbations from a nearby (4)Φ state.

Optical Stark spectroscopy of the 2(0)(6) Ã1A''-X̃1A' band of chloro-methylene, HCCl.

The laser induced fluorescence spectra of the 2(0)(6)Ã(1)A('')-X̃(1)A(') band of a rotationally cold (<20 K) molecular beam sample of chloro-methylene, HCCl, has been recorded, field-free and in the presence of a static electric field. The field-free spectrum has been analyzed to produce an improved set of spectroscopic parameters for the Ã(1)A('') (060) vibronic state. The magnitude of the a-component of the permanent electric dipole moment, µ(a), for the X̃(1)A(') (000) vibronic state has been determined to be 0.501(1) D from the analysis of the observed electric field induced shifts. Comparisons with theoretical predictions and flouro-methylene, HCF, are presented.

Tungsten monocarbide, WC: pure rotational spectrum and 13C hyperfine interaction.

The J = 1→2 pure rotational transitions in the X(3)Δ(1)(ν = 0) state of (186)W(12)C and (184)W(12)C were recorded using a pump/probe microwave optical double resonance (PPMODR) technique and analyzed to give fine structure parameters. The field-free [17.6]2←X(3)Δ(1) (1, 0) bands of the W(13)C isotopologues were recorded using laser induced fluorescence and analyzed to produce the (13)C(I = 1/2) magnetic hyperfine parameter. Bonding in the [17.6]2(ν = 1) and X(3)Δ(1)(ν = 0) states is discussed and a comparison of the experimentally determined properties of the X(3)Δ(1)(ν = 0) state with those predicted as a prelude to the electron electric dipole moment (eEDM) measurements [J. Lee, E. R. Meyer, R. Paudel, J. L. Bohn, and A. E. Leanhardt, J. Mod. Opt. 56, 2005 (2009)] is given.