Laser spectroscopy of the B[21.68]8-X8, B′[21.65]8-X8 and C[22.3]7-X27 transitions of holmium monofluoride

The spectrum of holmium monofluoride (HoF) in the blue (420-480 nm) region has been studied using laser-induced fluorescence. Previous work [J. Phys. B 7 (1974) L234] had assigned several bands in this region to the B8-X8 transition. By obtaining wavelength selected laser excitation spectra at high resolution and rotationally analyzing seven bands in this region, we have shown that not all the bands previously assigned to the B8-X8 system belong to the same electronic transition and have identified three separate transitions which we have labelled B8-X8, B′8-X8, and C7-X₂7. Preliminary low resolution dispersed fluorescence spectra have shown several excited states at energies greater than 4000 cm⁻¹ above the ground state and, though not all could be assigned, ligand field theory calculations are consistent with assigning them to the first excited spin-orbit component of the Ho⁺(4f¹⁰6s²)F⁻ ground state configuration or to the first excited configuration, Ho⁺(4f¹¹6s)F⁻. The results of the dispersed fluorescence experiments also tentatively place the X₂7 state at ∼70 cm⁻¹ above the ground X7 state.     

Laser spectroscopy of the A[16.4]8.5-X7.5, A[16.4]8.5-Y[0.15]8.5, and A[16.4]8.5-Z[0.85]7.5 transitions of dysprosium monochloride

Laser-induced fluorescence spectra have been obtained at low resolution using a laser ablation source and pulsed dye laser, and at high resolution using a Broida oven and cw ring dye laser. Dispersed fluorescence spectra from two different excited states, A[16.4]8.5 and B[15.4]Ω (unknown Ω) (the states are labelled [10⁻³T₀]Ω according to their energy and Ω assignment) showed transitions to the same four low lying electronic states, X7.5, Y[0.15]8.5, Z[0.85]7.5, and an unassigned state at 970 cm⁻¹. High resolution excitation spectra of the A-X 0-0, A-Y 0-0 and 0-1, and A-Z 0-0 and 0-1 transitions were obtained and a global fit to all the data yielded rotational constants for both ¹⁶²Dy³⁵Cl and ¹⁶⁴Dy³⁵Cl. From the band origins, vibrational frequencies of 291 and 284 cm⁻¹ were obtained for the Y[0.15]8.5 and Z[0.85]7.5 states, respectively, suggesting that these two states originate from the Dy⁺(4f¹⁰6s)Cl⁻ configuration. The ¹⁶²Dy-¹⁶⁴Dy and ³⁵Cl-³⁷Cl isotope effects were studied and both indicated a ground state, X7.5, vibrational frequency of ∼230 cm⁻¹ which was reinforced by the observation, in dispersed fluorescence from the B[15.4] state, of a weak transition to a state 233 cm⁻¹ above the ground state. The observed electronic states and their configurational origin are discussed in terms of ligand field theory predictions.     

Infrared emission studies of the AΣ-XΠ electronic transition of the SiC radical

The gas phase infrared emission spectrum of the A³Σ⁻-X³Π electronic transition of SiC has been observed using a high resolution Fourier transform spectrometer. Three bands ν′ − ν″ = 0-1, 0-0, and 1-0 have been observed in the 2770, 3723, and 4578 cm⁻¹ regions, where the 0-1 and 0-0 bands were observed for the first time. The SiC radical was generated by a dc discharge in a flowing mixture of hexamethyl disilane [(CH₃)₆Si₂] and He. A total of 1074 rotational transitions assigned to the 0-1, 0-0, and 1-0 bands have been combined in a simultaneous analysis with previously reported pure rotational data to determine the molecular constants for SiC in the two electronic states. The principal equilibrium molecular constants for the A³Σ⁻ state are: B_e = 0.6181195(18) cm⁻¹, α_e = 0.0051921(20) cm⁻¹, r_e = 1.8020884(26) Å, and T_e = 3773.31(17) cm⁻¹, with one standard deviation given in parentheses. The effect of a perturbation was recognized between the ν = 4 level of X³Π and the ν = 0 level of A³Σ, and the analysis was carried out to determine the interaction parameter between the two states.     

The visible spectrum of rhodium monoxide: RhO and RhO

Spectroscopic observations are reported for rhodium monoxide from hollow-cathode emission and laser-induced fluorescence experiments. Eleven bands of Rh¹⁶O and 10 of Rh¹⁸O, from the [15.8]²Π-X⁴Σ⁻ (b) and [16.0]²Π-X⁴Σ⁻ (b) transitions, have been rotationally analyzed. The ground state constants have been determined as B₀ = 0.4132, λ₀ = −0.58 and γ₀ = −0.102, in cm⁻¹. Rotational and lambda doubling parameters in v = 0, 1, 2, and 3 excited state vibrational levels have also been determined.     

Near infrared emission spectra of CoH and CoD

New high resolution emission spectra of CoH and CoD molecules have been recorded in the 640 nm to 3.5 μm region using a Fourier transform spectrometer. The bands were excited in a carbon tube furnace by the reaction of cobalt metal vapor and a mixture of H₂ or D₂ with He at a temperature of about 2600 °C. Eight bands were observed for the A′³Φ₄-X³Φ₄ electronic transition of CoD, and five bands for the corresponding transition of CoH. The (0, 0) bands of the A′³Φ₃-X³Φ₃ system were also recorded for both isotopologues, although one of the parity components in the X³Φ₃ sub-state of CoH was found to be perturbed. The A′³Φ₃-X³Φ₄ transition was also observed in our spectrum of CoH. In addition, a new [13.3]4 electronic state was found by observing [13.3]4-X³Φ₃ and [13.3]4-X³Φ₄ transitions in the spectrum of CoD. Analysis of the transitions with ΔΩ = 0, ± 1 provided more accurate values of spin-orbit splittings between Ω = 4 and Ω = 3 components. The ground-state data for both molecules were fitted both to band-constant and Dunham-expansion expressions, and a combined-isotopologue analysis of the X³Φ₄ spin component was carried out using the data for CoH and CoD. The upper states were represented by term values in these analyses because of perturbations, but estimated band constants for them were obtained in separate fits in which ground-state constants were held fixed.     

Laser spectroscopy of holmium monosulphide: Electronic, vibrational and rotational structure of the A[14.79]8.5-X8.5, A[14.79]8.5-W[0.25]7.5 and A[14.79]8.5-V[0.98]7.5 transitions

Laser induced fluorescence spectra of HoS have been obtained using a Broida oven and a ring dye laser. Dispersed fluorescence spectra showed transitions from a common upper state, A[14.79]8.5 to the v = 0 and 1 vibrational levels of three low lying states, labelled X8.5, W[0.25]7.5 and V[0.98]7.5 (the states are labelled [10⁻³T₀]Ω according to their energy and Ω assignment). High resolution excitation spectra were obtained for all six transitions and a rotational analysis yielded the following principal constants, in cm⁻¹, for the X, W and V states, respectively: T₀ = 0, 251.8713(31), 980.6969(37); B_e = 0.121903(42), 0.121729(37), 0.122561(34); ΔG_1/2 = 463.8811(46), 462.9411(45), 461.2084(127). For the A state, T₀ = 14794.6987(28) cm⁻¹ and B₀ = 0.112596(29) cm⁻¹. The three low lying states are shown to arise from the Ho²⁺[4f¹⁰(⁵I₈)6s]S²⁻ configuration in accord with Ligand Field Theory predictions. The atomic origin of each of the three low lying electronic states was determined from the observed resolved hyperfine structure.     

Laser spectroscopy of the B[17.7]8-X8 and C[19.3]9-X8 transitions of holmium monochloride

Several new transitions of holmium monochloride (HoCl) have been studied at high resolution using laser excitation spectroscopy. Two main transitions, B[17.7]8-X8 and C[19.3]9-X8 have been observed and five bands, 0-0, 0-1, 1-0, 1-1, and 2-1 of the B-X transition and three bands, 0-0, 0-1, and 0-3 of the C-X transition have been obtained at high resolution and rotationally analyzed. Among several low lying states observed in dispersed fluorescence was a strong transition from the C state to a state ∼2140 cm⁻¹ above the ground state. Excitation spectra of this transition have shown that there are apparently two states, ∼6 cm⁻¹ apart. Comparison with ligand field theory calculations are consistent with assigning these states to the excited low lying Ho⁺(4f¹¹6s)Cl⁻ configuration. Several other low lying electronic states have been observed in dispersed fluorescence spectra. Although their assignments could not be established, their energies suggest that they are from the Ho⁺(4f¹⁰6s²)Cl⁻ or Ho⁺(4f¹¹6s)Cl⁻ configurations. Rotational constants have been obtained for the B[17.7]8 and C[19.3]9 states and have been used to speculate on the possible electron configurations for these states.     

Fourier Transform Emission Spectroscopy of the FΣ-XΣ System of RuN

Emission spectra of RuN have been recorded at high resolution in the region 12 000-35 000 cm⁻¹ using a Fourier transform spectrometer. The molecules were excited in a ruthenium hollow cathode lamp in the presence of about 2.5 Torr of Ne and 5 m Torr of N₂. New bands with origins near 17 758.1, 18 866.4, 19 800.4 and 20 721.5 cm⁻¹ have been assigned as the 0-1, 0-0, 1-0, and 2-0 bands of a new ²Σ⁺-²Σ⁺ system with the lower state as the ground state. This transition has been labeled as F²Σ⁺-X²Σ⁺, with the F²Σ⁺ state arising from the 1σ²2σ²1π⁴1δ⁴4σ¹ configuration. A rotational analysis of these bands has been carried out and spectroscopic constants have been extracted. The principal equilibrium constants for the ground state of RuN are ΔG(1/2)″=1108.3235(22) cm⁻¹, B_e″=0.5545023(42) cm⁻¹, α_e″=0.0034468(57) cm⁻¹, r_e″=1.5714269(60) Å, while the equilibrium constants for the excited state are ω_e′=946.8471(40) cm⁻¹, ω_ex_e′=6.4229(14) cm⁻¹, B_e′=0.50085(21) cm⁻¹, α_e′=0.00375(10) cm⁻¹, r_e′=1.65345(34) Å. This transition is analogous to the E²Σ⁺-X²Σ⁺ system of RhC (W. J. Balfour et al., J. Mol. Spectrosc.198, 393 (1999)).     

The bΣ(b0) → XΣ(X10,X21) and aΔ(a2) → X21 transitions of AsBr

Emission spectra of the b¹Σ⁺(b0⁺) → X³Σ⁻(X₁0⁺,X₂1) and a¹Δ(a2) → X₂1 transitions of AsBr have been measured in the near-infrared spectral region with a Fourier-transform spectrometer. The arsenic bromide radicals were generated in fast-flow systems by reaction of arsenic vapor (As_x) with bromine and were excited by microwave-discharged oxygen. The most prominent features in the spectrum are the Δv = +1,0,−1, and −2 band sequences of the b¹Σ⁺(b0⁺) → X³Σ⁻(X₁0⁺) transition in the range 11 700-12 700 cm⁻¹. With lower intensities, the Δv = 0 and −1 sequences of the b¹Σ⁺(b0⁺) → X³Σ⁻(X₂1) sub-system show up in the same range. Further to the red, between 6000 and 6700 cm⁻¹, the Δv = 0, +1, and −1 sequences of the hitherto unknown a¹Δ(a2) → X₂1 transition are observed. Analyses of medium- and high-resolution spectra have yielded improved molecular constants for the X₁0⁺, X₂1, and b0⁺ states and first values of the electronic energy and the vibrational constants of the a2 state.     

Near-infrared Fourier-transform and millimeterwave spectra of the BiS radical

This paper reports the 6400-7400 cm⁻¹ Fourier-transform (FT) near-infrared (NIR) emission spectrum of the BiS X₂²Π_3/2 → X₁²Π_1/2 fine structure bands as well as the millimeterwave rotational spectrum of the X₁²Π_1/2 state. For the FTNIR observations, BiS was produced by reaction of bismuth with sulfur vapor and excited by energy transfer from metastable oxygen, O₂(a¹Δ_g), in a fast-flow system. As was the case for BiO [O. Shestakov, R. Breidohr, H. Demes, K.D. Setzer, E.H. Fink, J. Mol. Spectrosc. 190 (1998) 28-77], the 0.5 cm⁻¹resolution spectrum revealed a number of strong bands in the Δv = 0 and ±1 sequences which showed perturbed band spacings, band shapes, and intensities due to avoided crossing of the X₂²Π_3/2 and A₁⁴Π_3/2 potential curves for v^′ ? 4 of X₂²Π_3/2. The millimeterwave rotational spectrum of BiS in its X₁²Π_1/2 state was observed when BiS was produced in a high-temperature oven by a discharge in a mixture of Bi vapor and CS₂. The signal to noise ratio was markedly improved by using a White-type multipath cell. Ninety seven features from J′ = 23.5 to J′ = 41.5 were measured between 150 and 300 GHz. Analysis of the 0.5 cm⁻¹ resolution FT spectrum yielded the fine structure splitting and vibrational constants of the states. A simultaneous analysis of millimeterwave and a 0.005 cm⁻¹ FT spectrum of the 0-0 band of the NIR system was carried out to give precise rotational, fine, and hyperfine constants for the X₁²Π_1/2 and X₂²Π_3/2 states. The results are consistent with those reported earlier for BiO and indicate only a slight decrease in the unpaired electron density in the 6p(π^∗) orbital on the Bi atom.     

High-resolution infrared spectra of bicyclo[1.1.1]pentane

Infrared spectra of bicyclo[1.1.1]pentane (C₅H₈) have been recorded at a resolution (0.0015 cm⁻¹) sufficient to resolve for the first time individual rovibrational lines. This initial report presents the ground state constants for this molecule determined from the detailed analysis of three of the ten infrared-allowed bands, ν₁₄(e′) at 540 cm⁻¹, ν₁₇ (a₂″) at 1220 cm⁻¹, ν₁₈(a₂″) at 832 cm⁻¹, and a partial analysis of the ν₁₁(e′) band at 1237 cm⁻¹. The upper states of transitions involving the lowest frequency mode, ν₁₄(e′), show no evidence of rovibrational perturbations but those for the ν₁₇ and ν₁₈ (a₂″) modes give clear indication of Coriolis coupling to nearby e′ levels. Accordingly, ground state constants were determined by use of the combination-difference method for all three bands. The assigned frequencies provided over 3300 consistent ground state difference values, yielding the following constants for the ground state (in units of cm⁻¹): B₀ = 0.2399412(2), D_J = 6.024(6) × 10⁻⁸, D_JK = −1.930(21) × 10⁻⁸. For the unperturbed ν₁₄(e′) fundamental, more than 3500 transitions were analyzed and the band origin was found to be at 540.34225(2) cm⁻¹. The numbers in parentheses are the uncertainties (two standard deviations) in the values of the constants. The results are compared with those obtained previously for [1.1.1]propellane and with those computed at the ab initio anharmonic level using the B3LYP density functional method with a cc-pVTZ basis set.     

Spectroscopy of nickel chloride: Identification of the [15.0] Π3/2 and [15.0] Δ5/2 states

Vibrational bands belonging to the [15.0] ²Δ_5/2-A²Δ_5/2, [15.0] ²Δ_5/2-X²Π_3/2, and [15.0] ²Π_3/2-X²Π_3/2 electronic transitions of NiCl have been observed in the 14 000-16 000 cm⁻¹ region. The [15.0] ²Δ_5/2 and [15.0] ²Π_3/2 states are identified for the first time. The observed bands have been recorded at high spectral resolution using several techniques, which include intracavity laser spectroscopy (ILS), Fourier transform emission spectroscopy (FTS), and laser induced fluorescence (LIF) spectroscopy. For the ILS absorption spectra, NiCl molecules were produced in a nickel hollow cathode operated with a small amount of CCl₄. For the FTS emission spectra, excited NiCl molecules were produced in a King-type carbon tube furnace loaded with NiCl₂ and heated to 1600 °C. In the LIF work, NiCl molecules were produced by reacting laser-ablated nickel with PCl₃ seeded in argon. Detailed analysis of rotational transition lines indicates that the observed [15.0] ²Δ_5/2 and [15.0] ²Π_3/2 states are only separated by 10 cm⁻¹ and are interacting with each other. Molecular constants for these newly observed electronic states are reported.     

The AE-XA1 System of CaOCH3

We have recorded laser excitation spectra of the CaOCH₃ free radical in a laser ablation molecular beam apparatus, at a spectral resolution of about 0.010 cm⁻¹ and a rotational temperature estimated at 15 K. The two spin-orbit components of the A²E-X²A₁ 0₀⁰ origin band between 625 and 630 nm have been analyzed. Five main subbands were revealed, with ΔK=+1 and K″=0,±1,±2. There was clear evidence of lambda-doubling in the A²E_1/2-X²A₁ 0₀⁰ (F′₁) K′=+1←K″=0 component. A nonlinear least-squares fitting program based on the model developed by Endo et al. [Y. Endo, S. Saito, and E. Hirota, J. Chem. Phys.81, 122-135 (1984)] fit the experimental data (514 A-X lines, N″≤37) with a root mean square deviation of 0.003 cm⁻¹, using known molecular constants of the ground state. The main vibronic (T₀=15 925.1232(5) cm⁻¹), spin-orbit (aζ_ed=66.974 48(51) cm⁻¹), Coriolis (Aζ_t=5.437 30(24)) cm⁻¹, rotational (A=5.439 97(24) cm⁻¹, B=0.117 884(2) cm⁻¹), and fine structure constants (ε₁=−8.208(14)×10⁻³ cm⁻¹, h₁=1.50(12)×10⁻⁴ cm⁻¹, ε_aa=3.58(89)×10⁻³ cm⁻¹, ε_bc=3.20(76)×10⁻³ cm⁻¹) for the excited state have been obtained.     

High resolution emission spectroscopy of the AП-XΣ (red) system of CN

The emission spectra of the A²П-X²Σ⁺ (red) system of ¹²C¹⁴N have been reinvestigated in the 3500-22 000 cm⁻¹ region at high resolution using a Fourier transform spectrometer. In total, spectra of 63 bands involving vibrational levels up to v′ = 22 of the A²П state and v″ = 12 of the X²Σ⁺ ground state have been measured and rotationally analyzed providing an improved set of spectroscopic constants. The present measurements of the Δv = −2 sequence bands of ¹²C¹⁴N and those of ¹³C¹⁴N from Ram et al. (2010) [36] allow for a much improved identification of these two isotopologues in the near infrared spectra of carbon stars.     

Intracavity laser absorption spectroscopy of platinum fluoride, PtF

Two vibrational bands of an electronic transition of PtF occurring at 11 940 cm⁻¹ and 12 496 cm⁻¹ were recorded and analyzed. These transitions are identified as the (0,0) and (1,0) bands of an [11.9] Ω = 3/2 − XΩ = 3/2 electronic transition. Gas phase PtF was produced in a copper hollow cathode lined with platinum foil using a trace amount of SF₆, and the spectrum was recorded at Doppler resolution by intracavity laser absorption spectroscopy. This work represents the first published spectroscopic data on PtF. Molecular constants for the ground and excited electronic states are presented.     

High resolution Fourier transform spectrum of GaCl

The electronic emission spectrum of the A³Π₀-X¹Σ⁺ and B³Π₁-X¹Σ⁺ transitions of Gallium monochloride molecule (⁶⁹GaCl) has been recorded on BOMEM DA8 Fourier transform spectrometer at an apodized resolution of 0.035 cm⁻¹. The rotational structure of the 0-0, 1-0, 2-1, and 3-2, bands belonging to A-X and 0-0, 0-1, 1-2, and 0-2 bands belonging to B-X transitions has been analyzed and equilibrium rotational constants for the X¹Σ⁺ and A³Π₀ states have been obtained. For the first time we are able to determine the Λ-doubling constants in the v = 0 and 1 levels of the B³Π₁ state.     

Spectroscopy of NdO: New results

¹⁴²NdO molecules have been produced by heating ¹⁴²Nd₂O₃ to about 2100 K in a vacuum furnace in the presence of argon gas. A ring dye laser operating with DCM dye has been used to excite ¹⁴²NdO transitions in the 636-666 nm spectral region, and induced fluorescence has been spectroscopically analysed at high resolution with a Fourier transform spectrometer. Contributions from thermal emission have been simultaneously observed. Two new low-lying electronic states have been detected, at energies of about 2708 and 4139 cm⁻¹, designated as [2.7], most probably observed at ν = 1, and [4.1], likely to be (2)6 (observed at ν = 0). The ν = 1 level of the (1)6 state, already known at ν = 0, has been observed for the first time. Most levels pumped by the laser, between 14 000 and 17 400 cm⁻¹, could be identified from earlier work. In addition, by studying in more detail recently obtained fluorescence spectra [J. Mol. Spectrosc. 225 (2004) 132] spectroscopic constants have been improved for a number of states. Finally, from thermal emission spectra, rotational analyses of the 0-0 bands of two new systems, [16.4] − (2)5 and [14.1] − X4, and reanalyses at higher resolution of the 0-0 bands of the systems V, VII, VIII, and X have been carried out. A consistent set of spectroscopic constants of the levels of ¹⁴²NdO characterized as yet is presented.     

Doppler-limited CW infrared cavity ringdown spectroscopy of the ν1+ν3 OH + CH stretch combination band of jet-cooled methanol

A high resolution cavity ringdown spectrometer (CRDS) has been constructed using a 1.5 μm continuous-wave external-cavity tunable diode laser, a mode-matched near-confocal ringdown cavity, and 2 cm pulsed slit jet. Without signal averaging, the RMS noise in the absorption signal is 1.7 × 10⁻⁹ cm⁻¹. The rotationally resolved overtone spectrum of the OH(ν₁) + CH(ν₃) stretch combination band of methanol between 6510 and 6550 cm⁻¹ has been observed for J^′=0-8 and K^′=0-3 at sub-Doppler resolution. In total, 418 lines are assigned and global fits yield molecular torsion-rotation parameters for the upper state. Four K^′-localized perturbations are analyzed and the pattern of residuals is discussed.     

Direct observation of the D′ 2g(P2)-A′ Π(2u) system for Cl2 by laser induced fluorescence spectroscopy: Determination of the absolute position of the A′ state

In a discharged supersonic jet of Cl₂, transitions of the D′ 2_g(³P₂)-A′ ³Π(2_u) system for ³⁵Cl₂ were observed directly by laser induced fluorescence spectroscopy. By a discharge in Cl₂, the Cl₂ molecules were populated into the A′ state, which is a metastable and optically forbidden state, from the state. An ultraviolet laser radiation excites the molecules to the D′ ion-pair state. A set of Dunham parameters for the A′ state is determined from a global least-squares fitting for 59 vibronic bands with v″ = 0-7. In the fitting, the previously reported data, T(v) and B(v) for the v = 14 and 15 bands of the A′ state [T. Ishiwata, A. Ishiguro, K. Obi, J. Mol. Spectrosc. 147 (1991) 300-320], were included. Y₀₀ = 57295.723(5) cm⁻¹ of the D′ state [J.-H. Si, T. Ishiwata, K. Obi, J. Mol. Spectrosc. 147 (1991) 334-345] was also included in the global fitting in order to determine the absolute position of the A′ state. The determined parameters of the A′ state are Y₀₀ = 17171.506(14), Y₁₀ = 255.915(85), Y₂₀ = −4.465(70), Y₃₀ = −8.7(23) × 10⁻², Y₄₀ = 6.3(35) × 10⁻³, Y₅₀ = −4.9(26) × 10⁻⁴, Y₆₀ = 1.43(69) × 10⁻⁵, Y₀₁ = 0.16282(15), Y₁₁ = −2.363(68) × 10⁻³, Y₂₁ = −5.01(93) × 10⁻⁵, and Y₃₁ = −3.01(36) × 10⁻⁶ (in cm⁻¹ and one standard deviations of the fit in parentheses). The absolute position of the A′ state is determined with good accuracy.