Several new vibrational bands of the [15.9] B Ω=0⁺-X ³Σ⁻_{(Ω = 0⁺)} and [12.5] Ω=0⁺-X ³Σ⁻_{(Ω = 0⁺)} transitions of PtS have been recorded at high resolution using Intracavity Laser Spectroscopy (ILS). These new bands have been rotationally analyzed and incorporated into a comprehensive PtS data set that was fit to a mass-independent Dunham expression using PGOPHER. The comprehensive data set included all of the reported spectroscopic data for PtS, including: 32 FTMW transitions (estimated accuracy: 1 kHz) [Cooke and Gerry, J. Chem. Phys., 121, 3486 (2004)], 9 MODR transitions (25 kHz) [Li et al., J. Mol. Spec., 170, 310 (1995)], 51 mm- and sub-mm transitions (25-50 kHz) [Okabayashi et al., J. Mol. Spec., 248, 7 (2012)], 469 MB-LIF transitions (0.003 cm⁻¹) [Li et al.], and 4651 ILS transitions (0.005 cm⁻¹) [Handler et al., J. Mol. Spec., 263, 78 (2010) and from this work]. Deviations from the Dunham model were observed due to both the breakdown of the Born-Oppenheimer approximation and field-shift effects resulting from differences in nuclear charge density between Pt-isotopes. The observed field-shift effects extended to isotope-dependent shifts in electronic excitation energy, which have been reported previously only for PbS (and for PtF and PtCl in recent work by our group). The results of the analysis and a discussion of the deviations from the Dunham model will be presented.

Several vibrational bands of new electronic transitions of PtF and PtCl have been recorded in absorption using Intracavity Laser Spectroscopy (ILS). The PtX molecules were produced in current-regulated RF plasma discharges, operating with 0.30-0.80 A applied to a Pt-lined Cu hollow cathode in approximately 1 Torr of an Ar/He sputter gas mixture. A trace amount of SF₆ was used as the fluoride source for PtF, and a trace amount of CCl₄ was used as the chloride source for PtCl. The hollow cathode was located within the resonator cavity of either a DCM dye laser (14,500-16,500 cm⁻¹) or Ti:Sapphire laser (12,890-12,990 cm⁻¹; 13,255-13,365 cm⁻¹), and effective pathlengths of 0.4-2.0 km were utilized with the ILS method. Six vibrational bands were identified for PtF and eight vibrational bands were identified for PtCl. These band systems were assigned to the [15.8+x] Ω=5/2-B ²∆_5/2 transition of PtF and the [13.8] Ω=3/2-X ²Π_3/2 transition of PtCl. Both electronic transitions were fit to a mass-independent Dunham type Hamiltonian using PGOPHER. Isotope dependent deviations from the Dunham model were observed due to both Born-Oppenheimer breakdown and field-shift effects resulting from differences in nuclear charge density between Pt-isotopes. The results of the analyses will be presented.

The auto-ionization reaction Nd + O → NdO⁺ + e⁻ has been explored as a possible means for controlled modulation of the electron density in the thermosphere. High-altitude Nd release experiments have been conducted using sounding rockets, but the degree of ionization achieved was uncertain. The ionization energy (IE) of NdO is a key parameter for determination of the electron yield from the auto-ionization reaction, and the value available from the literature was of questionable accuracy. Resonantly enhanced two photon ionization (R2PI) was used to remeasure the IE. The value obtained, 5.5083(2) eV, was 0.54 eV higher than previous estimates. Combined with estimates of the NdO⁺ bond dissociation energy, our result indicates that the auto-ionization reaction is exothermic by 1.76(10) eV. Low energy states of NdO⁺ were examined using pulsed-field ionization zero kinetic energy photoelectron spectroscopy (PFI-ZEKE). A total of thirty vibronic levels arising from eight electronic states of NdO⁺ were observed. The pattern of electronic states indicates that the lowest energy electronic configuration is Nd³⁺(4f3)O²⁻, which agrees with electronic structure calculations and ligand field theory models.

Two new electronic transitions of TaF have been recorded at high resolution using Intracavity Laser Spectrscopy (ILS). The TaF molecules were produced in a current-regulated RF discharge operating with 0.35-0.40 A applied to a Ta-lined Cu hollow cathode. The hollow cathode was located within the resonator cavity of a dye laser, tunable over the 14,500-17,200 cm⁻¹range using DCM and R6G laser dyes. Effective pathlengths from 0.40-2.25 km were utilized with the ILS method. Five bands were observed with red-degraded bandheads near 15,366 cm⁻¹, 16,033 cm⁻¹, 15,630 cm⁻¹, 16,327 cm⁻¹, and 16,930 cm⁻¹that have been respectively assigned as the (0,0) and (0,1) bands of the [16.0] Ω=0-X Ω=0 transition of TaF, and (0,1), (0,0), and (1,0) bands of the [16.3] Ω=1-X Ω=0 transition of TaF. Rotational assignments for the transitions have been confirmed through combination difference analysis using the reported line positions of Ng et al. [J. Chem. Phys., 146, 094308 (2017)]. These line positions from Ng et al. were included in the PGOPHER fit of the newly observed transitions. Results of the analysis will be presented.

Six bands have been recorded at high resolution in absorption in the visible using Intracavity Laser Spectroscopy (ILS). The bands were observed in the current-regulated RF discharge resulting when 0.30 A was applied to a W-lined Cu hollow cathode, using approximately 300 mTorr of an Ar/H₂ sputter gas mixture with a trace amount of either CS₂ or SF₆. The hollow cathode was located within the resonator cavity of a DCM dye laser operating over the 14,500-16,500 cm⁻¹range, utilizing effective pathlengths of 0.2-1.0 km with the ILS method. The six observed bands are grouped currently into two vibrational progressions. The (0,0) bands have been identified by negligible W-isotope shifts, and have red-degraded bandheads near 15,050 cm⁻¹and 15,304 cm⁻¹. Both series have a vibrational separation of approximately 525 cm⁻¹, and preliminary rotational constants of 0.14 cm⁻¹. These values are consistent with the predicted spectroscopic constants for WS [Sevy et al., J. Phys. Chem. A, 121, 9446 (2017)], which has not been previously studied experimentally at high resolution. The inclusion of H₂ in the sputter gas mixture results in a roughly 10-fold increase in transition intensity. However, this increase in transition intensity is also observed if D₂ is added to the sputter gas mixture in place of H₂, with no observable rotational or vibrational shift for any of the observed bands. The transitions will be rotationally analyzed and fit using PGOPHER. The results of this analysis will be presented.

Beryllium is known to defy conventional bonding motifs in even the smallest of molecular systems. Notable diatomic examples of anomalous bonds include the Be dimer, and dative bonding in BeF⁻ anion. There is a fundamental interest in understanding how beryllium’s bonding characteristics develop with increasing molecular complexity. In the past year, we have moved forward with studies of triatomic species, specifically BeO₂⁻ and BeC₂⁻, through a combination of photoelectron velocity map imaging spectroscopy and ab initio computational methods. In this talk, we will present our current understanding of the bonding in these molecules, with comparisons to previously characterized diatomic molecules (BeO⁻, BeS⁻, BeF⁻).

Rotational spectra of LiNH₂ and NaNH₂ in their ~X¹A₁ ground electronic states have been recorded using pulsed-beam Fourier transform spectroscopy in the frequency range 22-58 GHz. These species were synthesized in a DC discharge by the reaction of ammonia and the respective laser-ablated alkali metal, in argon carrier gas. Observed transitions were analyzed with previously-measured millimeter-wave frequencies, improving previous rotational constants and determining the metal electric quadrupole hyperfine parameter, χ_aa, for both species. We find that χ_aa (Li) = 0.494 and χ_aa (Na) = -7.688. We also compare our results to DFT calculations. A Townes-Dailey analysis of the quadrupole constants suggest that the bonding of the –NH₂ ligand to lithium and sodium is comparable.

The millimeter-wave spectrum of the high spin radical chromium bromide, CrBr, in its X⁶Σ⁺ state has been measured using direct absorption methods between 220-300 GHz. The radical was created in a DC discharge by the reaction of dibromomethane with chromium vapor, produced in a Broida-type oven. This study is the first measurement of CrBr by any spectroscopic technique. Eight rotational transitions of four isotopologues (⁵²Cr⁷⁹Br, ⁵²Cr⁸¹Br, ⁵³Cr⁷⁹Br, and ⁵³Cr⁸¹Br) of this radical were recorded in the ground vibrational state, each consisting of fine structure sextets with additional bromine hyperfine splitting. Spectra were also obtained for the v=1 and v=2 states of ⁵²Cr⁸¹Br and ⁵²Cr⁷⁹Br. The data were fit with a Hund’s case b Hamiltonian and rotational, spin-spin, spin-rotation and hyperfine parameters were determined, including the higher order spin terms γ_s and Θ. The hyperfine constants indicate that CrBr has a significant covalent component to its bonding, unlike its chlorine and fluorine counterparts.

Lanthanide (Ln = La and Ce) atom reactions with water are carried out in a pulsed-laser ablation molecular beam source and characterized by mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical calculations. Both reactions yield Ln(OH)₂ as the main product through a hydrogen atom elimination of each water molecule. The MATI spectra of Ln(OH)₂ are dominated by the origin band and metal-ligand symmetric stretching and bending vibronic progressions. Adiabatic ionization energies measured from the spectra are 40135 (5) cm⁻¹for La(OH)₂ and 40756 (5) cm⁻¹for the Ce(OH)₂. The molecular symmetry of Ln(OH)₂ is C_2v, and the observed transitions are ¹A₁ - ²A₁ for La(OH)₂ and ²B₁ - ³B₁ for Ce(OH)₂. The ground valence electron configurations of La(OH)₂ and Ce(OH)₂ are La 6s¹ and Ce 4f¹6s¹, respectively. Ionization of each species removes a Ln 6s-based electron, and the resultant ion also has C_2v symmetry. The spectrum of Ce(OH)₂ has a broader linewidth than that of La(OH)₂, which is attributed to the unresolved spin-orbit levels by comparing with relativistic quantum calculations at the level of spin-orbit multi-reference quasi-degenerated perturbation theory. The metal-mediated hydrogen elimination of water is predicted to be thermodynamically and kinetically favorable by the density functional theory calculations.