Laser Excitation Spectroscopy of the Jet-Cooled Methoxy Radical Amidst Hydroxyl Transitions

Abstract

Laser-induced fluorescence excitation spectra of the methoxy radical have been recorded under high resolution in a supersonic jet expansion. The rotational structure associated with the 3¹ ₀ band of methoxy has been identified in the midst of strong overlapping rotational transitions due to the hydroxyl radical in the 32240 - 32580 cm^?1 spectral region. Rotationally-resolved à ²A₁ – [Xtilde] ²E spectra of the 3¹ ₀ band of methoxy have been explicitly assigned using the nomenclature for prolate symmetric top transitions in doublet states.     

High resolution Fourier transform infrared spectroscopy on CH2DI and CHD2I: evaluation of the ground state constants and analyses of the C-I stretching bands ν3

Abstract

The high resolution (0.0010cm^?1) Fourier transform infrared spectra of the partially deuterated methyl iodide molecules CH₂DI and CHD₂1 have been recorded and analysed in the ν₃ band regions around 510cm^?1. The fundamental band ν₃ is associated with the stretching of the C-I bond and the spectra appear therefore as an asymmetric rotor hybrid a/b-type band and hybrid a/c-type band for CH₂DI and CHD₂I, respectively. About 4700 transitions in the case of CH₂DI and about 3900 transitions in the case of CHD₂I have been assigned. The ground state rotational constants of CH₂DI and CHD₂I have been obtained using the ground state combination differences calculated from the assigned ν₃ transitions and 16 microwave transitions from literature. The S reduced Watson's Hamiltonian has been used in the calculations. In addition, the upper state parameters describing the v₃=1 vibrational states of these molecules have been determined. The obtained ground state constants as well as the upper state parameters have been compared to the corresponding constants of the symmetric top species CH₃I and CD₃I     

The υ1 fundamental bands of trans- and cis-DONO studied by high-resolution Fourier-transform spectroscopy

The absorption spectrum of deuterated nitrous acid DONO in the region from 2350 to 3000 cm⁻¹ has been recorded at a resolution of 0.003 cm⁻¹ using a Fourier-transform spectrometer. For the first time, 1366 a- and b-type transitions in the υ₁ fundamental band of trans-DONO and 741 b-type transitions in the υ₁ fundamental band of cis-DONO have been assigned. Rotational and centrifugal distortion constants up to sextic order were determined for the v₁ = 1 states of trans- and cis-DONO using non-linear least-squares calculations. Synthetic spectra calculated using the new rovibrational constants obtained for both species reproduce the observed spectra very well. In addition, the infrared transitions of this study were used, together with previously published pure rotational transitions, to determine improved rotational and centrifugal distortion constants of the ground states of trans- and cis-DONO.     

Lyman transitions of high rovibrationally excited H2, HD and D2 molecules

Energies and probabilities of Lyman transitions of high rovibrationally excited H₂, HD and D₂ molecules have been measured and compared with calculations. The experimental results are obtained from laser-induced fluorescence spectra that have been recorded in the spectral range from 60 500 to 83 500 cm⁻¹, covering 2/3 of the hydrogen Lyman band system. The necessary vacuum-UV radiation is produced by stimulated anti-Stokes Raman scattering, providing a widely tunable radiation source with narrow spectral bandwidth to resolve single Lyman transitions. The highest internal energies of detected hydrogen isotopologues are close to the dissociation limit. This extends the available data base of Lyman transitions from and to higher rotational states (J > 10) of HD and D₂.     

Pure Rotational Raman Spectra of Vapor Phase Methanols

Abstract

The rotational Raman spectra of four vapor phase isotopic methanols, CH₃OH, CH₃OD, CD₃OH and CD₃OD, have been reported for the first time in the wavenumber regions from 5 to 100–120 cm^?1. The major parts of the spectra consist of bands equispaced at 3.19, 3.04, 2.56 and 2.46 cm^?1 intervals, respectively, and have been interpreted as the pure rotational S-branch transitions.     

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.     

New measurements and global analysis of chloromethane in the region from 0 to 1800 cm

New high resolution Fourier transform spectra of pure ¹²CH₃³⁵Cl and ¹²CH₃³⁷Cl isotopomers of chloromethane have been recorded in Wuppertal covering the region from 600 to 3800 cm⁻¹. New rotational transitions within the v₂=1, v₅=1, and v₃=2 states have been measured at Lille. A first global analysis of the lower four band systems of the molecule (700-1800 cm⁻¹) is reported. The model was based on an effective Hamiltonian and dipole moment expressed in terms of irreducible tensor operators. A common set of 125 effective hamiltonian parameters (sixth order) has been adjusted to fit simultaneously some 11 000 IR data for each of the isotopomers including 153 mm wave data for 12CH₃35Cl. The assignments involve 12 sets of transitions (6 cold bands, 3 hot bands, and 3 pure rotational systems for ¹²CH₃³⁵Cl). The standard deviation was on average 0.00014 cm⁻¹ and 175 kHz for the IR and MMW data, respectively. The v₃=v₆=1 state was analysed for the first time principally from observed hot band transitions.     

Millimeter wave spectrum of HCS+1

High-resolution Fourier transform spectra have been used to measure precisely the line positions and intensities of the K′_a = 0–12 stacks of the ν₁ band of ¹⁴N¹⁶O₂ in the 1200–1850 cm^?1 region. Using a Hamiltonian which explicitly takes into account the Coriolis resonances between the (0 0 1) state and the (1 0 0) and (0 2 0) states, it has been possible to reproduce satisfactorily the rotational energy levels of the three interacting states {(0 2 0), (1 0 0), (0 0 1)} of ¹⁴N¹⁶O₂. An improved set of spin-rotation, rotational, and Coriolis coupling constants was determined for these three interacting states. In particular, we have been able to determine, for the (1 0 0) state, asymmetry-dependent constants such as (B - C) and (?_bb ? ?_cc) which could not be obtained in the previous work concerning the ν₁ band by M. Laurin and A. Cabana (J. Mol. Spectrosc.69, 421–434 (1978)). In addition, individual intensities of transitions belonging to the ν₁ band were measured, leading to the precise determination of the vibrational part of the transition moment operator of the ν₁ band together with five correcting rotational terms appearing in the expansion of this operator.     

The first high-resolution analysis of the low-lying ν9 band of propane

The ν₉ fundamental band (C-C-C deformation) of propane (C₃H₈) at 369 cm⁻¹ has been studied at high-resolution (0.0011 cm⁻¹) with spectra recorded using the synchrotron radiation from the French light source facility at SOLEIL coupled to a Bruker IFS 125HR Fourier transform spectrometer. A 2.526 m base multipass cell with optical paths from 10.296 to 151.78 m was used. In addition, a spectrum was also recorded using a conventional globar source. Comparison of these experimental spectra shows clearly the gain obtained on the signal-to-noise ratios with the synchrotron radiation. The spectra have been thoroughly analyzed and transitions up to J=65 and K_a=33 have been assigned. The upper-state rotational levels were fitted using an A-type Watson Hamiltonian written in the I^r representation. An accurate band center ν₀ (ν₉)=369.228080(25) cm⁻¹ as well as accurate rotational and centrifugal distortion constants have been obtained and used to simulate a synthetic spectrum. These parameters should be useful to simulate hot bands of propane involving the 9¹ vibrational level as their lower state.     

Doppler-limited dye laser excitation spectroscopy of the HSO radical

The cw dye laser excitation spectrum of the vibronic transition of the HSO radical was observed between 16 420 and 16 520 cm⁻¹ with Doppler-limited resolution, 0.03 cm⁻¹. The HSO radical was produced by reaction of discharged oxygen with H₂S or CH₃SH. The observed spectra were assigned to 751 transitions of the K′_a ← K″_a = 2 ← 3, 1 ← 2, 0 ← 1, 1 ← 0, 2 ← 1, and 3 ← 2 subbands, and were analyzed to determine rotational constants, centrifugal distortion constants, and spin-rotation interaction constants with good precision. The signs of the spin-rotation interaction constants were determined for both the upper and the lower state from the observed spectra. The band origin obtained is 16 483.0252 (2.5σ = 0.0013) cm⁻¹. The molecular constants which were determined reproduce the observed transitions with an average deviation of 0.0045 cm⁻¹.     

Vibration-rotation transitions in the CF radical, studied by laser magnetic resonance spectroscopy at 7.8 μm

Several transitions in the vibration-rotation spectrum of the CF radical in its X²Π state have been detected by CO-laser magnetic resonance. In addition to strong resonances for the ²Π_3/2-²Π_3/2 transitions in the fundamental band at 1286 cm⁻¹, weaker “cross” ²Π_3/2-²Π_1/2 and hot band transitions have also been observed. The ¹⁹F nuclear hyperfine splitting is clearly resolved for almost every transition. These observations provide an interesting comparison with the recent study of the same (1, 0) band of CF by diode laser spectroscopy.     

Observation of a forbidden vibrational absorption band of H2 in nanoporous aerogel

Room-temperature absorption spectra of H₂ in nanoporous aerogel with a pore diameter of ～20 nm have been studied on a Fourier spectrometer in the spectral range of 4000–4800 cm^?1. Absorption at the forbidden transitions of the 0–1 vibrational band has been observed. The recorded spectra of H₂ in aerogel have been compared with the spectra of free high-pressure H₂.     

Temperature dependence of nitrogen and oxygen broadening of the 16O3 ν 3 band

High-resolution Fourier transform absorption spectra of ozone broadened by N₂ and O₂ have been recorded at room temperature and at 225 K. Nitrogen- and oxygen-broadened half-widths and their temperature dependence for respectively 160 ro-vibrational transitions on the ¹⁶O₃ ν ₃ band with a wide range of rotational quantum numbers J (2–48) and K_a (0–8) have been determined.     

Rotational analysis of the (f0, e0)-X21 transition of the antimony monofluoride molecule

A rotational analysis is performed on the 0-0 band of the so called C₂ band system of antimony monofluoride. The results show that the band actually consits of two transitions designated as the f0⁺-X₂1 and e0⁻-X₂1 transitions.     

Measurement and analysis of the ν2 band of D216O

The rotational structure of the ν₂ band of D₂¹⁶O between 700 and 1550 cm^?1 has been analyzed from spectra recorded with a Fourier transform spectrometer (nominal resolution: 0.1 cm^?1). By applying Watson's reduced Hamiltonian and a least squares method to the set of observed transitions, together with microwave data and the infrared data of Williamson, 22 rotational constants for the ground state and 17 for the upper state have been obtained which predict the positions of more than 700 observed lines with a standard deviation of 0.04 cm^?1.     

The high-resolution infrared spectrum of the 201 band of carbonyl fluoride: Determination of the far infrared laser frequencies

The first high-resolution (0.0024 cm^?1) spectrum of the 2₀¹ band of COF₂ at 963 cm^?1 is reported. Nearly 4000 rotational transitions have been observed and assigned in the band between 936 and 990 cm^?1. The line positions are estimated to be accurate to 0.0001 cm^?1 (relative). The spectrum was calibrated using two adjacent bands of OCS. Approximately 1560 infrared transitions have been fitted simultaneously with the previously reported microwave data. The wave numbers of far infrared laser lines recently observed by Tobin and by Temps and Wagner have been calculated from the 2¹ energy levels, with estimated uncertainties of between 10^?5 and 10^?6 cm^?1.     

Intensity,transition moment,and bandshapes for the second overtone of compressed CO

Infrared spectra of the CO second overtone absorption band have been studied for pressures up to 156 bar. The absolute intensity, obtained from direct measurements of the total band, is found to be (1.27 ± 0.04) × 10^-2cm^-2Am^-1 at 298 K. Using the vibrational moments for the ground state and the transitions 0–1 to 0–4, we have evaluated the coefficients M₀ to M₄ of the quartic dipole moment function for CO and the coefficients of the vibration-rotation interaction functions. The normalized 0–3 band contours of compressed CO were first generated by summing the pressure-broadened rotational lines with Lorentz profiles. A discrepancy appears between calculated and observed bandshapes and increases with density. An empirical model, which involves the sum of CO self-broadened lines with profile described as the product of a Lorentz function by a fitted exponential function, gives reasonable agreement with the experiments. The interference effects resulting from overlapping lines have been estimated within the impact approximation.     

Diode laser jet spectra and analysis of the ν14 fundamental of 1,1,1,2-tetrafluoroethane (HFC-134a)

High resolution infrared spectra have been measured for mixtures of 1,1,1,2-tetrafluoroethane in Ne, expanded in a supersonic planar jet. The ν₁₄ fundamental is an essentially unperturbed C-type band, exhibiting many ΔK_c=±2 transitions. Accurate excited state rotational and distortion constants have been determined from an analysis of about 1250 transitions, by using Watson’s Hamiltonian in the S-reduction. A local perturbation has been observed with a crossing at K^′_a=11 for J^′ values between 17 and 18, and could be accounted for by a x-Coriolis interaction with a perturbing vibrational level of A^′ symmetry at about 1205.53(1) cm⁻¹. Due to the very efficient cooling in the jet, the rotational temperature resulted to be about 20 K, and no evidence of hot-band absorption was found.     

Measurement of rotational temperature in CO2 waveguide laser medium

A small-signal gain in CO₂ waveguide laser medium has been measured on rotational-vibrational transitions in the P-branch of the (0, 0, 1)-(0, 2⁰, 0) band. It has been found that the rotational temperature is well defined in the waveguide laser system where high excitation power is injected and a large amount of energy is flowing through vibrational, rotational, and translational degrees of freedom. The rotational temperature is slightly higher than the translational temperature.     

The diode-laser spectrum of the ν1 band of disulfur monoxide

The frequencies of approximately 460 transitions of the ν₁ band of the unstable molecule S₂O have been measured with an accuracy of ±0.001 cm^?1 using a diode-laser spectrometer. Effective constants for this band were produced by carrying out a least-squares fit on the infrared data plus 112 ground-state rotational transitions.