Fourier transform spectroscopy of N2O weak overtone transitions in the 1-2 μm region

The absorption spectrum of the natural sample of nitrous oxide has been recorded at Doppler limited resolution with a Fourier-transform spectrometer in the spectral range 5000-10 000 cm⁻¹. Ten cold bands (8Σ − Σ and 2Σ − Π), thirteen hot bands (11Π − Π, Σ − Σ, and Δ − Δ) of ¹⁴N₂¹⁶O and the 3ν₃ band of ¹⁴N¹⁵N¹⁶O have been newly detected. The uncertainty of the line position determination is estimated to be about 0.005 cm⁻¹ for unblended lines. The assignment of the spectrum has been done with the help of the prediction performed within the framework of the polyad model of effective Hamiltonian. The spectroscopic parameters G_v, B_v, D_v, H_v, and q_v have been determined for all newly detected bands. The line intensities of 13 weak bands have been measured. The uncertainty of the obtained line intensity values varies from 7 to 13%.     

The pure rotational spectrum of ZnO in the XΣ and aΠi states

The pure rotational spectrum of ZnO has been measured in its ground X¹Σ⁺ and excited a³Π_i states using direct-absorption methods in the frequency range 239-514 GHz. This molecule was synthesized by reacting zinc vapor, generated in a Broida-type oven, with N₂O under DC discharge conditions. In the X¹Σ⁺ state, five to eight rotational transitions were recorded for each of the five isotopologues of this species (⁶⁴ZnO, ⁶⁶ZnO, ⁶⁷ZnO, ⁶⁸ZnO, and ⁷⁰ZnO) in the ground and several vibrational states (v = 1-4). Transitions for three isotopologues (⁶⁴ZnO, ⁶⁶ZnO, and ⁶⁸ZnO) were measured in the a³Π_i state for the v = 0 level, as well as from the v = 1 state of the main isotopologue. All three spin-orbit components were observed in the a³Π_i state, each exhibiting splittings due to lambda-doubling. Rotational constants were determined for the X¹Σ⁺ state of zinc oxide. The a³Π_i state data were fit with a Hund’s case (a) Hamiltonian, and rotational, spin-orbit, spin-spin, and lambda-doubling constants were established. Equilibrium parameters were also determined for both states. The equilibrium bond length determined for ZnO in the X¹Σ⁺ state is 1.7047 Å, and it increases to 1.8436 Å for the a excited state, consistent with a change from a π⁴ to a π³σ¹ configuration. The estimated vibrational constants of ω_e ∼ 738 and 562 cm⁻¹ for the ground and a state agreed well with prior theoretical and experimental investigations; however, the estimated dissociation energy of 2.02 eV for the a³Π_i state is significantly higher than previous predictions. The lambda-doubling constants suggest a low-lying ³Σ state.     

Fourier transform emission spectroscopy of the EΠ-XΣ transition of CaH and CaD

The emission spectra of CaH and CaD have been recorded at high resolution using a Fourier transform spectrometer and bands belonging to the E²Π-X²Σ⁺ transition have been measured in the 20 100-20 700 cm⁻¹ region. A rotational analysis of 0-0 and 1-1 bands of both the isotopologues has been carried out. The present measurements have been combined with the previously available pure rotation and vibration-rotation data to provide improved spectroscopic constants for the E²Π state. The constants ΔG(½) = 1199.8867(34) cm⁻¹, B_e = 4.345032(49) cm⁻¹, α_e = 0.122115(92) cm⁻¹, r_e = 1.986633(11) Å for CaH, and ΔG(½)=868.7438(46) cm⁻¹, B_e = 2.212496(51) cm⁻¹, α_e = 0.036509(97) cm⁻¹, r_e = 1.993396(23) Å for CaD have been determined.     

Fourier transform spectroscopy of CO2 and OCO in the 3800-8500 cm region and the global modeling of the absorption spectrum of CO2

The absorption spectrum of the ¹⁸O enriched carbon dioxide has been recorded at Doppler limited resolution with a Fourier transform spectrometer in the spectral range 3800-8500 cm⁻¹. Seventeen cold bands (14Σ-Σ and 3Σ-Π) and nine hot bands (9Π-Π) of ¹²C¹⁸O₂, nineteen cold bands (18Σ-Σ and 1Σ-Π) and eighteen hot bands (6Σ-Σ, 9Π-Π and 3Δ-Δ) of ¹⁶O¹²C¹⁸O have been observed. Among them, 14 ¹²C¹⁸O₂ bands and 12 ¹⁶O¹²C¹⁸O bands are observed for the first time. The spectroscopic parameters G_v, B_v, and centrifugal distortion constants, have been determined for all observed bands. Effective Hamiltonian parameters for the ¹²C¹⁸O₂ isotopic species are retrieved from the global fitting of the observed line positions presented in this paper and collected from the literature. As the result, 65 obtained effective Hamiltonian parameters reproduce 5443 observed line positions of 73 ¹²C¹⁸O₂ bands with RMS = 0.00145 cm⁻¹.     

The laser-induced fluorescence study of AΣ-XΠi band system of CuS

The laser-induced fluorescence excitation spectra of jet-cooled CuS molecules have been recorded in the energy range of 17 200-19 500 cm⁻¹. Fourteen observed vibronic bands have been assigned as three transition progressions: A²Σ⁻ (v′ = 0-4)-X²Π_3/2 (v″ = 0), A²Σ⁻ (v′ = 0-4)-X²Π_3/2 (v″ = 1), and A²Σ⁻ (v′ = 0-3)-X²Π_1/2 (v″ = 0). Spectroscopic constants of both the X²Π ground state and the A²Σ⁻ excited state of ⁶³CuS and ⁶⁵CuS were determined by analyzing their rotationally resolved spectra. Furthermore, the lifetimes of most observed bands were measured for the first time.     

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.     

Sub-millimeter wave spectroscopy of the C3H radical: Ro-vibrational transitions from ground to the lowest bending state

Linear C₃H in its (X²Π) electronic ground state possesses strong Renner-Teller coupling in the two lowest bending modes, ν₄ and ν₅. The ²Σ^μ level of the v₄ = 1 bending mode is shifted towards lower energies and is supposed to lie only 20.3 cm⁻¹ above the ground state [S. Yamamoto, S. Saito, H. Suzuki, S. Deguchi, N. Kaifu, S. Ishikawa, M. Ohishi, Astrophys. J. 348 (1990) 363]. In the present study, first measurements of ro-vibrational transitions from the ²Π_3/2 ground state to the ²Σ^μ lowest vibrational state were performed using a Terahertz spectrometer equipped with a supersonic jet nozzle. Rotational levels of the ²Π_3/2 and v₄ = 1(²Σ^μ) state are close in energy and a crossing of the rotational energy ladders occurs between J = 24.5 and 25.5. A strong vibronic coupling leads to a significant intensity enhancement of ²Π_3/2 − ²Σ^μ ro-vibrational transitions. The search for ro-vibrational transitions was facilitated by measurements on pure rotational transitions in the ²Π_1/2, ²Π_3/2 and v₄ = 1(²Σ^μ) states, substantially extending the former data set published by Yamamoto et al. Data analysis yields an accurate value for the v₄ = 1(²Σ^μ) energy level which has been found to lie 609.9771(42) GHz or 20.34664(14) cm⁻¹ above the ²Π ground state. Furthermore, the value of the vibronic coupling constant β has been improved significantly and determined as 1231.77(51) MHz. The new set of spectroscopic parameters obtained in the present study permits very reliable frequency predictions into the Terahertz region.     

The rotational spectrum of BiO radical in its X1Π1/2 and X2Π3/2 states

Rotational spectra have been observed for BiO produced in a DC discharge through a low pressure mixture of O₂, Ar, and Bi vapor. Because of the highly non-thermal distribution of states, it has been possible to observe spectra arising from the X₁²Π_1/2 level up to v = 9 and for the X₂²Π_3/2 level up to v = 5 near 10 538 cm⁻¹. Precise rotational and hyperfine parameters have been determined for the observed states. By using available near infrared (NIR) data in a merged fit, the 0-0 and 1-1 fine structure intervals have been more precisely determined. Although the quality of the fit is very good, the interpretation of the hyperfine constants is complicated by relativistic effects and the interaction of the X₂ state with A₁⁴Π_3/2 state. The magnetic and quadrupole coupling constants will be compared with those of the Bi atom and related molecules.     

The electronic spectrum of AgBr2: Ab initio benchmark vs. DFT calculations on the lowest ligand-field states including spin-orbit effects

The X²Π_g, ²Σ_g⁺ and ²Δ_g states of AgBr₂ have been studied through benchmark ab initio CASSCF + Averaged Coupled Pair Functional (ACPF) and DFT calculations using especially developed valence basis sets to study the transition energies, geometries, vibrational frequencies, Mulliken charges and spin densities. The spin-orbit (SO) effects were included through the effective hamiltonian formalism using the |ΛSΣ〉 ACPF energies as diagonal elements. At the ACPF level, the ground state is ²Π_g, in contradiction with ligand-field theory and Hartree-Fock results. The ACPF adiabatic excitation energies of the ²Σ_g⁺ and ²Δ_g states are 3825 and 20 152 cm⁻¹, respectively. The inclusion of the SO effects leads to a pure Ω = 3/2 (²Π_g) ground state, a Ω = 1/2 (97% ²Π_g + 3% ²Σ_g⁺) A state, a Ω = 1/2 (3% ²Π_g + 97% ²Σ_g⁺) B state, a Ω = 5/2 (²Δ_g) C state and a Ω = 3/2 (99% ²Δ_g) D state. The B97, B3LYP and PBE0 functionals, which were shown to yield accurate transition energies for CuCl₂, overestimate the X²Π_g-²Σ_g⁺ T_e by around 25% but provide a qualitative energetic ordering in agreement with CASSCF and ACPF results. The nature of the bonding in the X²Π_g ground state is different from that of AgCl₂ since the Mulliken charge on the metal is 0.95 while the spin density is only 0.39. DFT strongly delocalizes the spin density providing even smaller values of around 0.13 on Ag not only for the ground state, but also for the ²Σ_g⁺ state.     

The sub-millimeter and Fourier transform microwave spectrum of HZnCl (X Σ)

The pure rotational spectrum of HZnCl (X ¹Σ⁺) has been recorded using sub-millimeter direct-absorption methods in the range of 439-540 GHz and Fourier transform microwave (FTMW) techniques from 9 to 39 GHz. This species was produced by the reaction of zinc vapor and chlorine gas with H₂ or D₂ in a d.c. glow discharge for the sub-millimeter studies. In the FTMW measurements, HZnCl was created in a discharge nozzle from Cl₂ and (CH₃)₂Zn. Between 5 and 10 rotational transitions were measured in the sub-millimeter regime for four zinc and two chlorine isotopologues; four transitions were recorded with the FTMW machine for the main isotopologue, each consisting of several chlorine hyperfine components. The data are consistent with a linear molecule and a ¹Σ⁺ ground electronic state. Rotational and chlorine quadrupole constants were established from the spectra, as well as an r_m⁽²⁾ structure. The Zn-Cl and Zn-H bond lengths were determined to be 2.0829 and 1.5050 Å, respectively; in contrast, the Zn-Cl bond distance in ZnCl is 2.1300 Å, longer by ∼0.050 Å. The zinc-chlorine bond distance therefore shortens with the addition of the H atom. The ³⁵Cl electric quadrupole coupling constant of eQq = −27.429 MHz found for HZnCl suggests that this molecule is primarily an ionic species with some covalent character for the Zn-Cl bond.     

The electronic spectrum of the SiC radical: A theoretical study

Electronic structure and spectroscopic properties of the low-lying electronic states of the SiC radical have been determined from the ab initio based configuration interaction calculations. Potential energy curves of 32 Λ-S states of singlet, triplet, and quintet spin multiplicities have been constructed. Spectroscopic constants (r_e, T_e, and ω_e) of 23 states within 6 eV are reported and compared with the existing data. The dipole moments (μ_e) of most of these states at their respective equilibrium bond lengths have been computed. Effects of the spin-orbit coupling on the spectroscopic properties of SiC have been studied. The E³Π state is found to be an important one which has not been studied before. A transition of the type E³Π-X³Π is predicted to take place in the range 25 000-26 000 cm⁻¹. The partial radiative lifetimes for several electric dipole allowed transitions such as A³Σ⁺-X³Π, B³Σ⁺-X³Π, C³Π-X³Π, D³Δ-X³Π, E³Π-X³Π etc. have been reported.     

The rotational spectrum of 13C2HD in the ground and excited bending states

The pure rotational spectrum of ¹³C₂HD was recorded in the range 100–700 GHz. Lines belonging to the ground vibrational state were observed from J^″ = 1 to J^″ = 11. Several absorption lines were also detected in the bending states v₄ = 1 (Π), v₅ = 1 (Π), v₄ = 2 (Σ⁺ and Δ), v₅ = 2 (Σ⁺ and Δ), v₄ = v₅ = 1 (Σ^?, Σ⁺ and Δ), v₄ = 3 (Π and Φ) and v₅ = 3 (Π and Φ). The transition frequencies measured in this work were fitted together with all the infrared lines available in the literature. The global fit allowed a very accurate determination of the vibrational, rotational and ?-type interaction parameters for the bending states of this molecule.     

Rovibrational laser jet-cooled spectroscopy of the NH3–Ar complex in the ν2 umbrella region of NH3: comparison between new infrared data and an ab initio calculated spectrum*

ABSTRACT

Five ortho and para bands of the ν₂ umbrella mode of the NH₃–Ar van der Waals complex have been recorded at high resolution using jet-cooled infrared laser spectroscopy. A rovibrational analysis provides accurate band centres and upper state rotational constants for the Π_s(j?=?1,k?=?0)?←?Σ_a(j,k?=?0) and Σ_s(j?=?1,k?=?0)?←?Σ_a(j,k?=?0) ortho bands. The puzzling para bands observed in the region of the lower and upper components of the inversion splitting doublet have been assigned by comparison with rovibrational and tunnelling levels and transitions calculated ab initio. The latter calculations are based on the four-dimensional potential energy surface reported by Loreau et al. [J. Chem. Phys. 141, 224303 (2014)], which takes explicitly into account the umbrella motion of the ammonia molecule. The very good agreement found between Π_s/a,lower(j?=?1,k?=?1)?←?Σ_a(j?=?1,k?=?1) and Π_s/a,upper(j?=?1,k?=?1)?←?Σ_s(j?=?1,k?=?1) experimental and calculated transitions has been exploited to determine precisely two different inversion splittings in the ν₂ state (32.003(1) and 36.008(1)?cm^?1) from extrapolated Q(0) line frequencies and to obtain a qualitative picture of Coriolis couplings present in both the ν₂?=?0 and ν₂?=?1 states.     

On the cΠ (v = 0) state of carbon monoxide

A full analysis of the near infrared c³Π-b³Σ⁺ (0-0) band is given and term values for both states determined. The c³Π (v = 0) state was jointly analysed with the perturbing k³Π (v = 2) state and data from the c³Π-X¹Σ⁺ (0-0) transition and 3A band system were included. It is shown that the available data are consistent with the c³Π (v = 0) state having near Hund’s case b coupling with a spin-orbit constant of A = 0.45 ± 0.02 cm⁻¹, a homogeneous perturbation with the k³Π (v = 2) state, and Λ-type doubling arising predominantly from its interaction with the j³Σ⁺ state. A discrepancy with a more recent report of the 3A band system is identified and discussed. The perturbed b³Σ⁺ state term values are consistent with a previously reported five state interaction model.     

A study of the AΠ-XΣ and BΣ-XΣ band systems of scandium monosulfide, ScS, using Fourier transform emission spectroscopy and laser excitation spectroscopy

Emission spectra of the A²Π_3/2-X²Σ⁺ (0, 1), (0, 0), and (1, 0) bands and the B²Σ⁺-X²Σ⁺ (0, 1), (0, 0), (1, 0), (2, 0), and (3, 1) bands of ScS have been recorded in the 10 000-13 500 cm⁻¹ region at a resolution of 0.05 cm⁻¹ using a Fourier transform (FT) spectrometer. The A²Π_r-X²Σ⁺ (1, 0) band as well as the B²Σ⁺-X²Σ⁺ (0, 0) and (1, 0) bands have been recorded at high resolution (±0.001 cm⁻¹) by laser excitation spectroscopy using a supersonic molecular beam source. The FT spectral features range up to N = 148, while those recorded with the laser cover the “low-N” regions. The lines recorded with the laser exhibit splittings due to the ⁴⁵Sc (I = 7/2) magnetic hyperfine interactions, which are large (∼6.65 GHz) in the X²Σ⁺ state and much smaller in the B²Σ⁺ and A²Π states. The energy levels were modeled using a traditional ‘effective’ Hamiltonian approach, and improved spectroscopic constants were extracted and compared with previous determinations and theoretical predictions.     

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.     

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.     

The Fourier Transform Emission Spectrum of BΠ1-XΣ Band-System of InCl

The emission spectrum of the B³Π₁-X¹Σ⁺ band-system of the InCl molecule has been recorded on a Fourier transform spectrometer at an apodized resolution of 0.025 cm⁻¹. The rotational structure of 1-0, 2-1, 0-0, 0-1, 1-2, 0-2, and 1-3 bands belonging to the B³Π₁-X¹Σ⁺ transition of In³⁵Cl has been analyzed and accurate equilibrium rotational constants of the B³Π₁ state, have been obtained. Precise Λ-doubling constants of the B³Π₁ state (v=0, 1, and 2) are also reported for the first time.     

Submillimeter-wave spectroscopy of VN (XΔr) and VO (XΣ): A study of the hyperfine interactions

The pure rotational spectra of VN (X³Δ_r) and VO (X⁴Σ⁻) have been recorded in the frequency range 290-520 GHz using direct absorption spectroscopy. These radicals were synthesized in the gas-phase from the reaction of VCl₄ with either N₂ or H₂O in an AC discharge. Seven rotational transitions were recorded for each molecule; in both sets of spectra, fine and hyperfine structures were resolved. The data sets for VN and VO were fit with Hund’s case (a) and case (b) Hamiltonians, respectively, and rotational, fine structure, and hyperfine constants determined. For VN, however, an additional hyperfine parameter, Δa, was necessary for the analysis of the Ω = 2 sublevel to account for perturbations from a nearby ¹Δ state, in addition to the usual Frosch and Foley constants. Determination of Δa suggests that the ¹Δ state lies ∼3000 cm⁻¹ above the ground state. In VO, the hyperfine structure in the F₂ and F₃ components was found to become heavily mixed due to an avoided crossing, predicted by previous optical studies to be near the N = 15 level. The hyperfine constants established for these two molecules are consistent with the proposed σ¹δ¹ and σ¹δ² electron configurations.     

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.