Precision infrared spectroscopy in CF379Br by means of infrared-microwave double resonance

From the observation of double resonance effects on the microwave spectrum two coincidences between 9.4 μm CO₂ laser lines and infrared transitions of the ν₆ → (ν₆ + ν₁) band of CF₃⁷⁹Br have been determined: R(30) laser line coincident with ^qR₂(7), F = 17/2→17/2 transition, R(28) laser line coincident with all four ΔF = 0 hyperfine components of the ^qQ₈(13) transition. In both cases other infrared transitions lay within the tuning range of the laser. The frequencies of these two laser lines allowed calculations of the band center frequency ν₀ = 1083.530 ± 0.001cm^?1 and α_A = 11.93 ± 0.3MHz, for the ν₆ → (ν₆ + ν₁) band.α_B constants were determined for the vibrational states v₆, (v₆ + v₁), v₁, and v₃.     

Microwave spectrum of the vibrational excited states ν6 and ν8 of formic acid: Contribution to the assignment of the Formic Acid Submillimeter Laser

The microwave spectrum of the ν₆ and ν₈ vibrationally excited states of H¹²COOH has been reinvestigated in the 10–200-GHz region, and 23 new transitions, essentially of the b type, were measured. The transitions allowed us to obtain a set of improved parameters for each of these two states which contribute to the assignment of the Formic Acid Submillimeter Laser. The vibrational energies of the ν₆ and ν₈ states have been derived from the assignment of infrared pump transitions and the corresponding submillimeter transition of the optically pumped submillimeter laser.     

The absorption of ethylene in the 10-μm region

The ν₇, ν₁₀, and ν₄ interacting band system has been studied from three complementary sources: classical, diode laser, and waveguide laser spectra. In addition to the two first-order Coriolis interaction terms associated with ζ_7.10^a and ζ_4.10^b, we were obliged to introduce the corresponding second-order terms to obtain a statistical agreement between calculated and experimental data. High-quality vibrational and rotational data are presented for the two infrared active fundamentals, ν₇ and ν₁₀, and the rotational constants for the inactive ν₄ fundamental are determined for the first time. We also present the list of all the infrared transitions starting from the vibrational ground state of ethylene and being in quasi coincidence with CO₂ or N₂O laser lines.     

Infrared-microwave two-photon spectroscopy of the ν4 and ν6 bands of D2CO

Transitions in the ν₄ and ν₆ bands of D₂CO have been recorded by means of an infrared-microwave two-photon spectometer. The two-photon frequencies have been combined with frequencies obtained by infrared laser Stark and microwave spectroscopy to obtain rotational and centrifugal distortion constants for the ground, ν₄, and ν₆ states as well as vibrational frequencies and the Coriolis coupling constant for the two excited states. Expressions are reported for the linestrengths of two-photon transitions for an asymmetric rotor for the cases of parallel and perpendicular orientation of the planes of polarization of the infrared and microwave radiation.     

Laser Stark spectroscopy of the coriolis coupled ν2 and ν5 bands of CD3Cl

About 940 Stark resonances for CD₃³⁵Cl and 610 resonances for CD₃³⁷Cl have been measured by using a CO₂ laser with the 9- and 10-μm regions. They were assigned to 59 rovibrational transitions of ν₂ (J′ ≤ 37, K ≤ 14) and 200 of ν₅ (J′ ≤ 47, ?14 ≤ k′l′ ≤ +10) for ³⁵Cl, and 31 of ν₂ (J′ ≤ 12, K ≤ 10) and 175 of ν₅ (J′ ≤ 46, ?14 ≤ k′l′ ≤ +9) for ³⁷Cl. These data, combined with the microwave and FIR data in the ν₂ and ν₅ states, were analyzed by taking account of the Coriolis interaction between ν₂ and ν₅, and the (2, 2) and (2, ?1) interactions in ν₅. Several ΔK = +2 transitions of the ν₅ band were observed in the Stark spectra, and the ground state constants, A₀ and D_K0, were determined precisely for both ³⁵Cl and ³⁷Cl species. Also, the vibrationally induced dipole moments were obtained. The molecular constants and the zero-field transition frequencies of the ν₂ and ν₅ bands were determined.     

Laser-microwave double-resonance spectroscopy in CF3I with four CO2-laser lines

Double-resonance effects produced by three CO₂-laser lines, the 9.4-μmR(12),R(14), and R(18), have been newly observed. From an analysis of the observed laser-induced changes in intensity of various microwave transitions, the infrared transitions which were accidentally coincident with these three laser lines were determined. In every case an exact rotational assignment of the infrared transition was possible, but in some cases the assignment of the vibrational band involved was difficult. When the previously discussed (l) effects produced by the R(16) laser line are included these four consecutive laser lines pump a total of seven infrared transitions of CF₃I. It appears that all seven transitions belong to different fundamental, combination, and hot bands.     

Identification of hot band transitions of CH4 near 3000 cm

Rovibrational transitions between vibrationally excited states of ¹²CH₄ in the 3.4 μm wavelength region are investigated by a pump-probe technique using an optical parametric oscillator as a pump and a tunable diode laser as a probe. Methane molecules are excited into selected levels of the 2ν₃ state of the tetradecad and numerous transitions between pentad and tetradecad, and between tetradecad and triacontad, have been observed in this spectral range. Positions and assignments of transitions involving a level of the 2ν₃ (F₂) substate are reported. Reliable energy values for 2ν₃ (F₂) levels up to J = 6 are obtained, and the energies and assignments of a number of 3ν₃ levels have been deduced allowing identification of IR lines in the 1.1 μm region.     

Microwave spectrum of formic acid and its isotopic species in D, 13C and 18O. Study of Coriolis resonances between ν7 and ν9 vibrational excited states

In the investigation of the 8 → 280 GHz region, 241 and 57 transitions of H¹²COOH and DCOOH, respectively, have been assigned to the ν₇ and ν₉ vibrational states coupled by a strong Coriolis resonance. The numerical analysis based on Watson's theory of centrifugal distortion coupled with the addition of Coriolis interaction allows us to obtain a set of parameters which fits the transitions well. The rotational spectra of the isotopic species HCOOD and DCOOD have also been investigated. In this investigation 55 and 67 transitions have been assigned to the ν₇ and ν₉ vibrational states of these two molecules, respectively. A very weak Coriolis resonance was detected. Two non-rigid independent rotors were thus employed and gave us a set of parameters which fits the transitions quite well. The rotational spectrum of the ground state of H¹²COOH, H¹³COOH, HCOOD, DCOOH, H¹²C¹⁶O¹⁸OH, and H¹²C¹⁸O¹⁶OH have been reinvestigated and a set of improved parameters was obtained for each species.     

Collisional transfer of rotational energy in the 2B1 electronic state of nitrogen dioxide

Collisional satellite lines have been observed in fluorescence from nitrogen dioxide excited by the 4545-Å line of the argon laser. The 13_0,13 level of the (0, 8, 0) vibrational state is populated by the laser and undergoes collisionally induced transitions to the 11_0,11, 15_0,15, and 17_0,17 states. These collisionally populated states are identified by their fluorescence to the well-studied (0, 0, 0) and (0, 1, 0) levels of the ground electronic state. These satellite lines are also observed in fluorescence to the (0, 2, 0) and (0, 3, 0) vibrational levels of the ground electronic state. The wavenumbers of those lines, together with those from unrelaxed fluorescence and previously published microwave transitions, allow vibrational and rotational constants for the higher vibrational states to be determined more accurately than was previously possible. Several much weaker forbidden transitions have also been observed, including ΔK_a = 0 through ?6 transitions in the (0, 8, 0)-(0, 0, 1) band.     

Spectroscopy of the ν5 band of CDF3 by heterodyne measurement of SMMW laser emission frequencies

Submillimeter wave laser action has been previously reported in deuterated fluoroform (CDF₃) which is optically pumped by a CO₂ laser. In this paper, accurate frequency measurements are reported for 23 laser emissions. Of these lines, 21 can be assigned to the ν₅ degenerate vibrational state. The data were fitted with a theoretical expression for the transitions containing terms up to sixth order in J and K and also containing all important doubling effects. The quality of the fit was very good, yielding accurate values for many of the molecular constants of the ν₅ state.     

Temperature dependence of rotational relaxation of methane in the 2ν3 vibrational state by self- and nitrogen-collisions and comparison with line broadening measurements

Depopulation rates of rotational levels in the v₃ = 2 vibrational state of ¹²CH₄ are investigated by a pump-probe technique. Methane molecules are excited into selected rotational levels by tuning the pump laser to 2ν₃ lines. The time evolution in population of the excited level after the pumping pulse is monitored by tuning the probe laser to a (3ν₃ ← 2ν₃) line corresponding to a transition with the excited rotational level as the lower level. Measurements were performed from room temperature down to 100 K in pure CH₄ and in CH₄-N₂ mixtures. The rotational relaxation rate coefficients are given for the J = 1, A₂, J = 1, E, J = 1, F₂ and J = 0, F₂ levels. The results are compared with the available data on line broadening coefficients. The temperature dependence of the data on N₂-broadening is particularly well reproduced by the power law deduced from the results on rotational relaxation.     

Simultaneous analysis of the ν1, ν4, 2ν2, ν2 + ν5, and 2ν5 infrared bands of 12CH3F

The Fourier-transform spectrum of CH₃F from 2800 to 3100 cm^?1, obtained by Guelachvili in Orsay at a resolution of about 0.003 cm^?1, was analyzed. The effective Hamiltonian used contained all symmetry allowed interactions up to second order in the Amat-Nielsen classification, together with selected third-order terms, amongst the set of nine vibrational basis functions represented by the states ν₁(A₁), ν₄(E), 2ν₂(A₁), ν₂ + ν₅(E), 2ν₅⁰(A₁), and 2ν₅^±2(E). A number of strong Fermi and Coriolis resonances are involved. The vibrational Hamiltonian matrix was not factorized beyond the requirements of symmetry. A total of 59 molecular parameters were refined in a simultaneous least-squares analysis to over 1500 upper-state energy levels for J ≤ 20 with a standard deviation of 0.013 cm^?1. Although the standard deviation remains an order of magnitude greater than the precision of the measurements, this work breaks new ground in the simultaneous analysis of interacting symmetric top vibrational levels, in terms of the number of interacting vibrational states and the number of parameters in the Hamiltonian.     

The rotation-vibration constants of the 12CH3F ν3 band

Accurate rotational and vibrational constants for the ground and the ν₃ states of ¹²CH₃F are derived from a simultaneous least-squares fit of all the previous microwave, laser Stark and far-infrared laser data related to the ν₃ ← 0 band. Spectroscopic data, concerning the far-infrared laser emission in ¹²CH₃F, are discussed.     

Measurements of spatially resolved electron number densities and modes temperatures using optical emission spectroscopy of atmospheric pressure microplasma jet

The electrical gas discharge parameters of direct-current non-thermal microplasma jet in Ar-2%H₂ flow at open atmospheric air was investigated by using spatially resolved optical emission spectroscopy (OES). The jet was confined from microhollow of tungsten-carbide (～500 μm inner diameter) to a molybdenum foil. Despite its small volume, the atmospheric pressure microplasma jet provides a range of power densities, from low to ～10¹² W m^?3 generated either in rare gases or in molecular gases. A high resolution spectrometer (Jobin-Yvon, Czerny-Turner model THR1000, resolution of 0.001 nm, with focal length of 1.0 m and numerical aperture of 0.13 ? f/7.5) was used to allow registration of OH (A ²Σ⁺, ν = 0 → X ²Π, ν′ = 0) rotational bands at 306.357 nm, Ar I 603.213 nm line and N₂ (C ³Π _u , ν = 0 → B ³Π _g , ν′ = 0) second positive system with the band head at 337.13 nm in order to estimate the rotational temperature from the cathode sheath of the plasma jet to the anode. For currents ranging from 20 to 100 mA and for a particular excited levels, the excitation temperature was measured in the negative glow region either from a Boltzmann plot of Ar I 4p–4s and 5p–4s transitions of excited argon or using the Mo I (from 440 to 450 nm) two-lines method of excited Mo atoms sputtered from the cathode surface, giving 24 000 K (100 mA at 100 μm) and 7000 K (20 mA at 500 μm from the cathode). From the N₂ (C ³Π _u , ν = 0 → B ³Π _g , ν′ = 0) rotational transition the rotational temperature along the positive column was estimated. The vibrational temperature of the bulk plasma (1400 to 4500 K) was estimated for a current varying from 20 to 120 mA using the N₂ second positive system with Δν = ?2. Using the broadening of H _β Balmer line it was possible to estimate the electron number density of the negative glow (10¹⁴ to 10¹⁵ cm^?3) as a function of the current.     

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.     

Optoacoustic laser Stark spectroscopy in the ν2 band of 14NH3

Laser Stark spectroscopy of the R(5, K) transitions in the ν₂ band of ammonia was carried out using coincidences with the 9-μm band CO₂ laser lines. We observed 22 Doppler-free resonances by using an optoacoustic detector and a Lamb-dip stabilized CO₂ laser. A simultaneous analysis of sa, aa, and ss lines yields zero-field transition frequencies with an absolute accuracy of 1 ～ 2 MHz.     

Infrared laser magnetic resonance (LMR) spectroscopy of NO2 (ν2) with a CO2 laser

The infrared laser magnetic resonance spectra for the ν₂ band of NO₂ were observed by using a CO₂ laser. High-K vibration-rotation transitions from ^rR₆(N) to ^rR₁₁(N) (v₂ = 1 ← 0) were observed. The analysis yielded some molecular parameters including two g factors for the excited vibrational state (v₂ = 1).     

Analysis of the rotational spectrum of pyruvonitrile up to 324 GHz

The room-temperature rotational spectrum of pyruvonitrile (acetyl cyanide, CH₃COCN) was measured up to 324 GHz, and additional measurements were also made in supersonic expansion in the region 7-19 GHz. The available data sets for the A and E torsional sublevels were extended to over 1200 transitions, J = 65 and K_a = 38 for the ground vibrational state, and to comparable numbers of transitions for first excited states of the methyl torsional mode ν₁₈, and the in-plane CCN bending mode ν₁₂. The collected experimental measurements were fitted with several different computer programs for dealing with the effects of methyl torsional motion on the rotational spectrum and many spectroscopic constants have been determined. The experimental results are discussed in detail and are augmented by ab initio computations. Stark effect measurements in supersonic expansion were used to precisely determine the electric dipole moment of pyruvonitrile, ∣μ_a∣ = 2.462(2) D, ∣μ_b∣ = 2.442(2) D, μ_tot = 3.468(2) D. Pyruvonitrile, as an 8-atom molecule with a sizable dipole moment, is a possible candidate for astrophysical detection and the present work provides the laboratory data necessary for that purpose.     

Rotational spectrum of trans-trans diethyl ether in the ground and three excited vibrational states

We report the results of a comprehensive reinvestigation of the rotational spectrum of diethyl ether based on broadband millimetre-wave spectra recently recorded at The Ohio State University and in Warsaw, covering the frequency region 108-366 GHz. The data set for the ground vibrational state of trans-trans diethyl ether has been extended to over 2000 lines and improved spectroscopic constants have been determined. Rotational spectra in the first excited vibrational states of the three lowest vibrational modes of trans-trans-diethyl ether, ν₂₀, ν₃₉, and ν₁₂ have been assigned. The v₂₀ = 1 and v₃₉ = 1 states are near 100 cm⁻¹ in vibrational term value and are coupled by a strong c-axis Coriolis interaction, which gives rise to many spectacular manifestations in the rotational spectrum. All of these effects have been successfully fitted for a dataset comprising over 3000 transitions, leading to precise determination of the energy difference between these states, (ΔE/hc)=10.400222(5) cm⁻¹. A newly developed software package for assignment and analysis of broadband spectra is described and made available.     

The Δk = ±2 perturbation-allowed ν4 band and inversion-rotation energy levels of 15NH3

More than 800 Δk = ±2 and 60 Δk = ±3 forbidden transitions to the ν₄ and 2ν₂ vibrational levels, respectively, have been assigned in the Fourier transform spectra of ¹⁵NH₃, recorded with a pathlength of 96 m. Combination differences derived from these transitions provide information on the spacing between the ground state energy levels with different rotational quantum numbers K in the interval from 0 to 16. These data along with wavenumbers of all the available allowed transitions pertaining to the ground and ν₂ states have been subjected to a simultaneous least-squares analysis using two different parametrization models to obtain precise values of the inversion-rotation energy levels.