Frequency measurement of pure rotational transitions of OH

Frequencies of pure rotational transitions of OH⁻ ion were measured in the 1-5 THz region with a high-precision tunable far-infrared spectrometer. The measured frequencies were analyzed together with the data of infrared measurements to refine rotational parameters.     

The Lamb-dip spectrum of the J + 1 ← J (J = 0, 1, 3-8) transitions of HCN: The nuclear hyperfine structure due to H, C, and N

The pure rotational J + 1 ← J transitions, with J = 0, 1, 3-8, of H¹³CN have been observed in the millimeter- and submillimeter-wave region using the Lamb-dip technique to resolve the hyperfine structure due to H, ¹³C, and ¹⁴N. The present observations allow us to provide for the first time the spin-rotation constant of ¹³C and the spin-spin interaction constant S₁₂ (between H and ¹³C) as well as to remarkably improve the quadrupole coupling and spin-rotation constants of ¹⁴N. In addition, a good empirical estimation of C_I(H), based on ab initio calculations, has also been provided. Furthermore, our frequencies together with previous data permit to determine the most accurate ground state rotational parameters known up to now.     

The pure rotational spectrum of TiS (XΔr) at submillimeter wavelengths

The pure rotational spectrum of TiS in its X³Δ_r ground state has been measured using millimeter-wave direct-absorption techniques in the frequency range of 313-425 GHz. This free radical was created by the reaction of titanium vapor, produced in a high-temperature Broida-type oven, with H₂S. Eight to ten rotational transitions were recorded for the main titanium isotopologue, ⁴⁸TiS, in the v = 0 and v = 1 levels, as well as for the v = 0 state of ⁴⁶TiS, observed in natural abundance (⁴⁸Ti:⁴⁶Ti = 74:8). All three Ω components were observed in almost every recorded transition, with no evidence for lambda-doubling. The data were fit with a Hund’s case(a) Hamiltonian, and rotational, spin-orbit, and spin-spin constants were determined, as well as equilibrium parameters for ⁴⁸TiS. Relatively few fine structure parameters were needed for the analysis of TiS (A, A_D, and λ), unlike other 3d metal species. The rotational pattern of the three fine structure components suggests the presence of a nearby excited ¹Δ state, lying ∼3000 cm⁻¹ higher in energy. From the equilibrium parameters, the dissociation energy for TiS was estimated to be ∼5.1 eV, in reasonable agreement with past thermochemical data.     

15N216O在1650-3450 cm-1的高分辨红外光谱

采用傅里叶变换红外光谱仪记录了富含¹⁵N₂¹⁶O同位素的一氧化二氮样品在1650-3450 cm^-1波段的高分辨振转光谱,得到了该同位素分子超过7300吸收谱线位置的实验值,经分析实验精确度好于5.0×10^-4 cm^-1. 基于有效哈密顿量模型预测和带带转动分析,确定了所有吸收线的归属;获得了29个新吸收带的振转光谱参数,并优化了其他44个吸收带的光谱参数值. 并且发现有效哈     

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.     

Spectroscopic constants of the ground and lower vibrational states of CH2BrF: A combined high resolution infrared and microwave study

The enriched ⁸¹Br isotopic species of bromofluoromethane has been investigated in the infrared and microwave regions. The rovibrational spectrum of the ν₅ fundamental has been studied by high resolution FTIR spectroscopy, while the rotational spectra of the ground and v₆ = 1 states have been observed by means of microwave spectroscopy. More than 2700 transitions have been assigned in the ν₅ band and the analysis of the rovibrational structure reveals a first-order c-type Coriolis resonance with the v₆ = 2 state. The present study improves the ground state constants available in the literature and enables the determination of further centrifugal distortion parameters together with the full bromine quadrupole coupling tensor. A set of spectroscopic parameters up to the sextic distortion terms for the vibrational excited states has been accurately evaluated for the first time.     

High sensitivity cw-cavity ringdown and Fourier transform absorption spectroscopies of CO2

The absorption spectrum of ¹³CO₂ has been recorded by cw-cavity ringdown spectroscopy with a new set up based on fibered DFB lasers. By using a series of 31 DFB lasers, the spectrum of carbon dioxide could be recorded in the 6130-6750 cm⁻¹ region with a typical sensitivity of 5 × 10⁻¹⁰ cm⁻¹. The spectrum has also been recorded between 4400 and 8500 cm⁻¹ with a Fourier transform spectrometer associated with a multi-pass cell (maximum path length of 105 m). The new observations obtained both by FTS and CRDS represent a significant extension of the available data. For instance, more than 4000 line positions were measured and assigned in the CRDS spectrum while only 232 line positions are listed in the HITRAN database. Altogether, the band by band analysis has led to the determination of the rovibrational parameters of 65, 7, and 24 bands for the ¹³C¹⁶O₂, ¹⁶O¹³C¹⁷O, and ¹⁶O¹³C¹⁸O isotopomers, respectively. As some observed line positions show significant deviations from the predictions of the effective Hamiltonian model, the new observed line positions were gathered with the data available in the literature to refine the set of effective Hamiltonian parameters of the ¹³C¹⁶O₂ isotopic species. The refined set of 96 effective Hamiltonian parameters reproduces more than 14 650 line positions of ¹³C¹⁶O₂ with an RMS=0.002 cm⁻¹. A detailed comparison with the line positions retrieved from Venus spectra and the line list provided by HITRAN is also presented and discussed.     

Emission spectroscopy of a new Δ-1Δ system of VO

High-resolution spectra of VO have been reinvestigated in the 12 000-31 000 cm⁻¹ region. VO was produced in a vanadium hollow cathode lamp by discharging 1.5 Torr of Ar and the spectra were recorded using a Fourier transform spectrometer. The oxygen needed to produce VO was present in the system as an impurity. Three new bands observed in the 21 000-22 100 cm⁻¹ region have been attributed to a new ²Δ-1²Δ electronic transition of VO. Two bands, with origins near 21 044 and 22 038 cm⁻¹, have been assigned as the 0-1 and 0-0 bands of the ²Δ_3/2-1²Δ_3/2 sub-band while a weak band with an origin near 21 975 cm⁻¹ has been assigned as the 0-0 band of the corresponding ²Δ_5/2-1²Δ_5/2 sub-band. A rotational analysis of these sub-bands has been obtained and spectroscopic constants have been extracted. The 1²Δ state is known from the previous analyses of the doublet transitions of VO in the near infrared. The present observation has allowed the determination of the vibrational interval ΔG_1/2 and the equilibrium rotational constants for the 1²Δ_3/2 state.     

Rotational Spectra of XeH and Its Isotopic Species

Frequencies of rotational transitions of XeH⁺ and its isotopic species were measured in the 1–5 THz region with a highprecision far-infrared spectrometer using a tunable radiation source. Measured frequencies were analyzed together with previous microwave and infrared measurements to refine mass-independent Dunham parameters.     

Torsion-rotation far-infrared spectrum of O-18 methanol

High-resolution Fourier transform spectra have been recorded from 15–470 cm^–1 for the far-infrared trosion-rotation band of O-18 methanol in the vibrational ground state. So far, 57 subbands have been assigned in the 15–220 cm^–1 region for a wide range of rotational and torsional states, and their J-independent origins have been determined to an estimated accuracy of ±0.01 cm^–1. The observed origins were found to deviate in many cases by several tenths of a cm^–1 from the values calculated with the previous molecular parameters. Together with 4 known microwave origins, the new data have been fitted to a model torsion-rotation Hamiltonian in order to refine the set ofb-type molecular constants for the ground state. With the new parameter set, the experimental subband origins are reproduced with an rms error of ±0.02 cm^–1, representing a substantial improvement over the earlier situation. The spectroscopic results have also been of great assistance with our assignments of optically-pumped FIR laser emission in CH₃ ¹⁸OH, in providing FIR data for checking the identification of the IR-pump/FIR-laser transition systems through combination loop relations.     

Analysis of the first triad of interacting states (0 2 0), (1 0 0), and (0 0 1) of D2O from hot emission spectra

The far-infrared and middle-infrared emission spectra of deuterated water vapour were measured at temperatures 1370, 1520, and 1940 K in the ranges 320-860 and 1750-3400 cm⁻¹. The measurements were performed in an alumina cell with an effective length of hot gas of about 50 cm. More than 3550 new measured lines for the D₂¹⁶O molecule corresponding to transitions from highly excited rotational levels of the (0 2 0), (1 0 0), and (0 0 1) vibrational states are reported. These new lines correspond to rotational states with higher values of the rotational quantum numbers compared to previously published determinations: J_max = 29 and K_a(max) = 22 for the (0 2 0) state, J_max = 29 and K_a(max) = 25 for the (1 0 0) state, and J_max = 30 and K_a(max) = 23 for the (0 0 1) state. The extended set of 1987 experimental rotational energy levels for the (0 2 0), (1 0 0), and (0 0 1) vibration states including all previously available data has been determined. For the data reduction we used the generating function model. The root mean square (RMS) deviation between observed and calculated values is 0.004 cm⁻¹ for 1952 rovibrational levels of all three vibration states. A comparison of the observed energy levels with the best available values from the literature and with the global predictions from molecular electronic potential energy surfaces of water isotopic species [H. Partridge, D.W. Schwenke, J. Chem. Phys. 106 (1997) 4618] is discussed. The latter confirms a good consistency of mass-dependent DBOC corrections in the PS potential function with new experimental rovibrational data.     

Ground state rotational spectrum of nitrogen trifluoride: The K = 3 splittings of NF3 and NF3

The ground state rotational spectrum of the ¹⁴NF₃ and ¹⁵NF₃ isotopic species of nitrogen fluoride has been observed in the ∼450-810 GHz frequency range. This investigation allowed us to improve the rotational parameters for both isotopologues. In particular, for the first time the K = 3 line splitting parameter and the sextic centrifugal distortion constants have been determined for ¹⁵NF₃.     

Rotational levels of the (0 0 0) and (0 1 0) states of D2O from hot emission spectra in the 320-860 cm region

The far-infrared emission spectra of deuterated water vapour were measured at different temperatures (1370, 1520, and 1950 K) in the range 320-860 cm⁻¹ at a resolution of 0.0055 cm⁻¹. The measurements were performed in an alumina cell with an effective length of hot gas of about 50 cm. More than 1150 new measured lines for the D₂¹⁶O molecule corresponding to transitions between highly excited rotational levels of the (0 0 0) and (0 1 0) vibrational states are reported. These new lines correspond to rotational states with higher values of the rotational quantum numbers compared to previously published determinations: J_max=26 and for the (0 0 0) ← (0 0 0) band, J_max=25 and for the (0 1 0) ← (0 1 0) band, and J_max=26 and for the (0 1 0) ← (0 0 0) band. The estimated accuracy of the measured line positions is 0.0005 cm⁻¹. To our knowledge no experimentally measured rotational transitions for D₂¹⁶O within an excited vibrational state have been available in the literature so far. An extended set of experimental rotational energy levels for (0 0 0) and (0 1 0) vibration states including all previously available data has been determined. For the data reduction we used the generating function model. The root mean square (RMS) deviation between observed and calculated values is 0.0012 cm⁻¹ for 692 rotational levels of the (0 0 0) state and 0.0010 cm⁻¹ for 639 rotational levels of the (0 1 0) vibrational state. A comparison of the observed energy levels with the best available values from the literature and with the global predictions from molecular electronic potential energy surface [J. Chem. Phys. 106 (1997) 4618] for the (0 0 0) and (0 1 0) states is discussed.     

Pure rotational spectrum and structural determination of silacyclopentane

The ground state pure rotational spectrum of silacyclopentane (SCP) has been investigated using both Fourier Transform Microwave (FTMW) and chirped pulse Fourier Transform Microwave (cp-FTMW) spectroscopies. In addition to the parent species, the spectra of the ¹³C, ²⁹Si and ³⁰Si singly-substituted isotopologues were recorded in the 6–24 GHz region in natural abundance. Structural analysis confirms that the ground state has C₂ symmetry and the geometric parameters determined based on heavy atom substitution include the bond distances, bond angles and dihedral angles of the SCP ring backbone.     

The ν1 + 3ν2 + 3ν3 and 4ν1 + ν2 + ν3 bands of ozone by CW-cavity ring down spectroscopy between 5900 and 5960 cm

The absorption spectrum of ozone, ¹⁶O₃, has been recorded in the 5903-5960 cm⁻¹ region by high sensitivity CW-cavity ring down spectroscopy (α_min ∼ 5 × 10⁻¹⁰ cm⁻¹). The ν₁ + 3ν₂ + 3ν₃ and 4ν₁ + ν₂ + ν₃ A-type bands centred at 5919.15 and 5947.07 cm⁻¹ were newly observed. A set of 173 and 168 energy levels could be experimentally determined for the (1 3 3) and (4 1 1) states, respectively. Except for a few K_a = 5 levels of the (4 1 1) state, the rotational structure of the two states was found mostly unperturbed. The spectroscopic parameters were determined from a fit of the corresponding line positions by considering the (1 3 3) and (4 1 1) states as isolated. The determined effective Hamiltonian and transition moment operators were used to generate a list of 785 transitions given as Supplementary Material.     

Millimeter-Wave Spectroscopy of ClBS: An Improved Evaluation of the Equilibrium Structure of Chlorothioborine

The rotational spectrum of the unstable ClBS molecule has been investigated in the millimeter-wave region, from 80 to 195 GHz. A high-temperature reaction between crystalline boron and disulfur dichloride vapor was used to produce the molecule in a flow pyrolysis system. Eight different isotopic species were studied measuring lines in the ground and excited vibrational states 01¹0 (ClBS bend), 10⁰0 (ClB stretch), 02⁰0, 02²0, and 00⁰1 (BS stretch). The analysis of the spectra has been performed taking simultaneously into account both the Fermi resonance between the 10⁰0 and 02⁰0 states, and l-type resonance effects in the v₂=2 vibrational state. This procedure allowed us to calculate directly deperturbed rotational constants, from which the equilibrium rotational constant of seven isotopic variants could be accurately determined yielding a much improved evaluation of the equilibrium structure of chlorothioborine: r_e(ClB)=1.6806±0.0001 Å and r_e(BS)=1.6049±0.0001 Å. The equilibrium structures of ClBS and of the related molecules HBS, FBS, HCP, FCP, and ClCP have been also theo-retically evaluated by high-level CCSD(T) calculations performed using cc-pVTZ, cc-pVQZ, and cc-pV5Z basis sets. The different trends respectively observed for the BS and CP bond lengths in the XBS and XCP triatomic molecules are discussed.     

The C hyperfine constants of HCS and HSC studied by microwave spectroscopy

The ¹³C hyperfine constants of the H¹³CS and HS¹³C radicals are determined by microwave spectroscopy. For H¹³CS, the 1₀₁-0₀₀ rotational transition is measured at 38.5 GHz with a Fourier transform microwave spectrometer, and two ¹³C hyperfine constants are determined. They are well interpreted in terms of a relatively large HCS bonding angle (132.8°). For HS¹³C, the N=7-6, 9-8, and 10-9 rotational transitions are measured in the 268-384 GHz region by using a source modulation spectrometer combined with a free-space discharge cell, and five ¹³C hyperfine constants including the nuclear spin-rotation constant, C_aa, are determined. From the ¹³C hyperfine constants, the p character of the unpaired electron orbital on the carbon atom is estimated to be 66.5%, supporting a classical resonance picture; .     

Highly sensitive absorption spectroscopy of carbon dioxide by ICLAS-VeCSEL between 8800 and 9530 cm

The absorption spectrum of carbon dioxide has been studied between 8800 and 9530 cm⁻¹ by intracavity laser absorption spectroscopy based on a vertical external cavity surface emitting lasers (VeCSEL). Previous laboratory spectra at high resolution were nearly absent in the considered spectral region. Experiments were carried with natural carbon dioxide and with ¹³C enriched carbon dioxide leading to the determination of the rovibrational parameters of a total of 15 very weak vibrational transitions, including two bands of the ¹⁶O¹³C¹⁸O isotopologue. The observed transitions are assigned to components of the 2ν₁ + 3ν₃ triad and of the much weaker 5ν₁ + ν₃ hexad. Our measured line positions are found in excellent agreement with the predictions of the effective Hamiltonians developed for ¹²C¹⁶O₂ and ¹³C¹⁶O₂ but significant deviations were evidenced for the ¹⁶O¹³C¹⁸O minor isotopologue. The relative band intensities within each polyad are also discussed on the basis of the effective Hamiltonian model.