The v6 = 1 and v6 = 2 vibrational states of DCF3

The high-resolution infrared spectra of DCF₃ were reinvestigated in the ν₆ fundamental band region near 500 cm⁻¹ and around 1000 cm⁻¹ with the aim to assign and analyze the overtone level of the asymmetric CF₃ bending vibration v₆ = 2.The present paper reports on the first study of both its sublevels (A₁ and E corresponding to l = 0 and ±2, respectively) through the high-resolution analysis of the overtone band and the hot and bands.The well-known “loop method”, applied to and , yielded ground state energy differences Δ(K, J) = E₀(K, J) − E₀(K − 3,J) for the range of K = 6 to 30.In the final fitting of molecular parameters, we used the strategy of fitting all upper state data together with the ground state rotational transitions.This is equivalent to that calculating separately the and coefficients of the K-dependent part of the ground state energy terms from the combination loops.All rotational constants of the ground state up to sextic order could be refined in the calculation.This led to a very accurate determination of C₀ = 0.18924413(25) cm⁻¹, , and also .In the course of analyzing simultaneously the overtone band together with the and ν₆ bands, the original assignment of the fundamental ν₆ band [Bürger et al., J. Mol. Spectrosc. 182 (1997) 34-49] was found to be incompatible with the present one. Assignments of the (k + 1, l₆ = +1)/(k − 1,l₆ = −1) levels had to be interchanged, which changed the value of Cζ₆ = −0.14198768(26) cm⁻¹ and the sign of the combination of constants C − B − Cζ in the v₆ = 1 level to a negative value.     

High-resolution infrared and subterahertz spectroscopy of the v2 = 1, v5 = 1, and v3 = 2 levels of CH3Cl

High-resolution Fourier-transform infrared spectra between 1235 and 1680 cm⁻¹ and subterahertz spectra between 250 and 630 GHz of monoisotopic ¹³CH₃³⁵Cl have been recorded and analyzed simultaneously, with all Coriolis, α-resonance, and l-type interactions in the polyad of the v₂ = 1, v₅ = 1, and v₃ = 2 levels taken into account. Several α-resonances (Δk = ±2, Δl = ?1) generating perturbation-allowed transitions have been assigned in the rovibrational spectra. These resonances enabled us to determine accurately and independently the ground state rotational and centrifugal distortion parameters A₀ = 5.205 746 9 (55) cm⁻¹ and . Even , which is, however, correlated to higher-order α-resonance terms, was determined. With 51 upper state parameters varied, about 5800 rovibrational wavenumbers and more than 550 rotational frequencies pertaining to the excited vibrational states were fitted within their experimental accuracy.     

Frequency measurement of pure rotational transitions in the v2 = 1 state of H2O

Frequencies of pure rotational transitions in the v₂ = 1 vibrationally excited state of H₂¹⁶O were measured with a tunable far-infrared spectrometer in the frequency range of 0.5-5 THz. Molecular parameters of Watson’s A-reduced Hamiltonian have been obtained to reproduce the observed frequencies.     

Accurate rotational spectroscopy of sulfur dioxide, SO2, in its ground vibrational and first excited bending states, v2 = 0, 1, up to 2 THz

Approximately 150 pure rotational transitions each have been recorded for SO₂, v₂ = 0 and 1, in selected frequency regions up to 2 THz. The J and K_a quantum numbers reach very high values: 92 and 23, respectively, for the ground vibrational state and 81 and 21, respectively, for the first excited bending state. The highest levels accessed are almost 3000 cm⁻¹ above ground. The relative experimental uncertainties Δν/ν are about 10⁻⁸ for several medium to strong, isolated lines, and generally better than 2.5 × 10⁻⁷. Improved spectroscopic parameters have been obtained for both states, particularly for the excited bending state. In fact, the accuracies with which the energy levels of the v₂ = 1 state are known depend essentially only on the accuracy with which the vibrational spacing is known from infrared spectroscopy.     

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.     

High-resolution FTIR and MMW study of the v4 = 2 (A1, E) excited state of NF3 near 985 cm: the axial ground state rotational constants derived by the “loop-method”

The two substates v₄ = 2⁰ (A₁, 983.702 cm⁻¹) and v₄ = 2^±2 (E, 986.622 cm⁻¹) of the oblate symmetric top molecule, ¹⁴NF₃, have been studied by high-resolution (2.5 × 10⁻³ cm⁻¹) infrared spectroscopy of the overtones and 2ν₄ − ν₄ hot bands. Transitions of the overtone, the hot band, and the previously measured fundamental band were combined to yield 585 ground state combination differences differing in K by ±3, with K_max = 36. Using the “loop-method,” a fit (standard deviation σ = 0.320 × 10⁻³ cm⁻¹) provided a complete set of the hitherto not experimentally known axial ground state constants. In units of cm⁻¹ these have the following values: . Upper state parameters were determined using a vibrationally isolated model. Considering l (2, 2) and l (2, −1) interactions between the v₄ = 2⁰ and v₄ = 2^±2 substates and effects accounting for the l (4, −2) interactions within the kl = −2 levels, 25 upper state parameters were obtained by fitting 2747 IR data (1842 transitions, 905 deduced energies, J_max = 42, K_max = 39) with σ_IR = 0.353 × 10⁻³ cm⁻¹. Moreover, millimeter-wave spectroscopy furnished 86 transitions (J_max = 16, K_max = 13) measured on the v₄ = 2 excited state. A merged fit, refining 24 parameters using the described model gave σ_IR = 0.365 × 10⁻³ cm⁻¹ andσ_MMW = 0.855 × 10⁻⁶ cm⁻¹ (26 kHz). The anharmonicity constants (in cm⁻¹) are x₄₄ = −0.84174 (2) and g₄₄ =  + 0.73014 (1). In addition to this model, the D, Q, and L reductions of the rovibrational Hamiltonian were tested. Standard deviations σ_IR = 0.375 × 10⁻³ cm⁻¹ and σ_MMW = 0.865 × 10⁻⁶ cm⁻¹ were obtained for both D and L reductions, and σ_IR = 0.392 × 10⁻³ cm⁻¹ and σ_MMW = 0.935 × 10⁻⁶ cm⁻¹ for Q reduction. The unitary equivalence of the majority of the 18 tested relations between the derived parameters was satisfactorily fulfilled. This confirms that the v₄ = 2 excited vibrational state can be considered in reasonable approximation to be isolated.     

Spectroscopy of XY3Z (C3v) molecules: A tensorial formalism adapted to the O (3) ⊃ C∞v ⊃ C3v group chain

A tensorial formalism adapted to the case of XY₃Z symmetric tops has been developed. We use the O (3) ⊃ C_∞v ⊃ C_3v group chain. All the coupling coefficients and formulas for the computation of the matrix elements are given for this chain. Such relations are also deduced in C_3v group itself.     

High-resolution study of the ν1 + ν2 and ν2 + ν3 strongly interacting bands of D2Se

A high-resolution Fourier transform spectrum of the D₂^MSe species (M = 82, 80, 78, 77, and 76) in the region 2300-2500 cm⁻¹ was recorded for the first time and assigned. On the basis of these experimental data, rotation-vibration energies of the (1 1 0) and (0 1 1) vibrational states were fitted, and band centers, and rotational, centrifugal distortion, and resonance interaction parameters were determined for the main D₂⁸⁰Se species. The obtained set of 32 fitted parameters reproduces the 647 rotation-vibration energies with a rms deviation of 0.00024 cm⁻¹. The ν₁ + ν₂ and ν₂ + ν₃ bands of the other four isotopic species are analyzed as well.     

Sub-Doppler and Doppler spectroscopy of DCN isotopomers in the terahertz region: ground and first excited bending states (v1v2v3)=(0 1 0)

The rotational spectra of the deuterium cyanide isotopic species DCN, D¹³CN, DC¹⁵N, and D¹³C¹⁵N were recorded in the vibrational ground and first excited bending state (v₂=1) up to 2 THz. The R-branch transitions from J=3←2 to J=13←12 were measured with sub-Doppler resolution. These very high resolution (∼70 kHz) and precise (±3-10 kHz) saturation dip measurements allowed for resolving the underlying hyperfine structure due to the ¹⁴N nucleus in DCN and D¹³CN for transitions as high as J=10←9. Additional high JR-branch (J=25←24 to J=28←27) transitions around 2 THz and direct l-type (ΔJ=0, J=19 to J=25) transitions from 66 to 118 GHz were recorded in Doppler-limited resolution. For the ground state of D¹³C¹⁵N, the J=1←0 transition was measured for the first time. The transition frequency accuracies for the other deuterated species were significantly improved. These new experimental data, together with the available infrared rovibrational data and previously measured direct l-type transitions, were subjected to a global least squares analysis for each isotopomer. This yielded precise sets of molecular constants for the ground and first excited vibrational states, including the nuclear quadrupole and magnetic spin-rotation coupling constants of the ¹⁴N nucleus for DCN and D¹³CN. The hyperfine structure due to the D, ¹³C, and ¹⁵N nuclei have not been resolved, but led to a broadening of the observed saturation dips.     

Sub-Doppler high-resolution excitation spectroscopy of the S1 ← S0 transition of dibenzofuran

Rotationally resolved ultrahigh-resolution fluorescence excitation spectra of the S₁ ← S₀ transition of dibenzofuran have been observed using the technique of crossing a collimated molecular beam and the single-mode UV laser beam. 3291 rotational lines of the band and 3047 rotational lines of the band have been assigned. The band has been found to be a b-type transition, in which the transition moment is along the twofold symmetry axis of this molecule, and only the ΔK_a = ± 1 transitions were observed. The excited state is identified to be the S₁¹A₁(ππ^∗) state. In contrast with this, the band has been found to be an a-type transition in which the transition moment is along the long axis in plane. It indicates that the intensity of this vibronic band arises from vibronic coupling with the S₂¹B₂(ππ^∗) state. We determined the accurate rotational constants and the molecule have been shown to be planar both in the ground and excited states.     

High-precision frequency measurements of the ν1 + ν3 combination band of C2H2 in the 1.5 μm region

A pair of 1.5 μm semiconductor laser frequency standards have been developed for optical telecommunications use, stabilised to transitions of ¹²C₂H₂ and ¹³C₂H₂, using cavity-enhanced Doppler-free saturation absorption spectroscopy. The absolute frequencies of 41 lines of the ν₁ + ν₃ band of ¹²C₂H₂, covering the spectral region 1520-1545 nm, have been measured by use of a passive optical frequency comb generator, referenced to ¹³C₂H₂ transitions of known frequency. The mean experimental uncertainties (coverage factor k = 1) of the frequency values are 3.0 kHz (type A) and 10 kHz (type B). Improved values of the band origin ν₀, rotational constants B′ and B″, and centrifugal distortion coefficients D′, D″, H′, and H″ are presented.     

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.     

Fourier transform emission spectroscopy of Δv = 2 sequence bands of the CO molecule in the ground electronic state

High-resolution emission spectroscopy of rovibrational Δv = 2 sequence bands is carried out from a low-pressure discharge through pure CO gas. The effect of rare gases on the production of the Δv = 2 sequence bands is also studied. The v′ → (v′-2) sequence bands up to v′ = 17 are observed. Bands involving 8 ? v′ ? 17 in the Δv = 2 sequence are reported for the first time. The 16-14 and 17-15 bands could be observed only in the presence of xenon as a buffer gas. Accurate molecular constants (T, B, D, H) for different vibrational states of the ground electronic state of ¹²C¹⁶O are determined from a global fit.     

The far-infrared spectrum of acrolein, CH2CHCHO: The ν18 fundamental and (ν17 + ν18) − ν18 hot bands

The ν₁₈ fundamental band (∼158 cm⁻¹) of acrolein is studied at high resolution (0.0015 cm⁻¹) using synchrotron radiation from the Canadian Light Source facility and a Bruker IFS 125HR Fourier transform spectrometer. By fitting this band, together with some pure rotational transitions, molecular parameters are obtained to accurately determine the energies of the ν₁₈ = 1 state levels for values of (J, K_a) up to at least (45, 24). These parameters should be useful for future high resolution studies of acrolein hot bands. This is demonstrated here by a detailed analysis of the (ν₁₇ + ν₁₈) − ν₁₈ hot band at ∼589 cm⁻¹. The upper state (ν₁₇ + ν₁₈) of this band is found to be perturbed by Coriolis interactions analogous to those affecting the ν₁₇ state.     

Microwave and sub-mmwave study of CH3SiH3 including the perturbation-allowed torsion-vibration difference band (ν12=0,ν6=3)↔(ν12=1,ν6=0)

The vibration-torsion-rotation Hamiltonian in CH₃SiH₃ has been investigated using Fourier transform microwave methods and tunable sideband far-infrared spectroscopy. Four different studies have been carried out. First, the Q-branch of the torsion-vibration difference band (ν₁₂=0,ν₆=3)↔(ν₁₂=1,ν₆=0) has been measured between 17.8 and 26.6 GHz. When three quanta of the torsional mode ν₆ are excited in the ground vibrational state (gs) for (σ=−1) torsional sublevels with K=6, these transitions become allowed through resonant Coriolis-like coupling to the lowest lying degenerate mode ν₁₂ with no quanta of ν₆ excited. Second, direct l-doubling transitions in the state (v₁₂=1, v₆=0) have been observed between 8.3 and 17.5 GHz for both torsional sublevels σ=0 and σ=±1. In the limit that the intervibrational interactions vanish, the σ-splitting between lines of the same J would be difficult to resolve, but frequency differences of more than 1 GHz due to these interactions have been determined. Third, the (J=1←0) spectrum just below 22 GHz has been re-measured with higher resolution for 0?v₆?4 in the gs and for (v₆=0) in ν₁₂. Finally, the (J=45←44) spectrum near 1 THz has been obtained for 0?v₆?2 in the gs. A global data set of 3423 frequencies has been formed by merging the present 123 measurements with the data set used recently in the simultaneous analysis of the ν₁₂ and ν₅ bands by Schroderus et al. [J. Chem Phys. 115 (2001) 1392]. By refining the (gs/ν₁₂/ν₅) Hamiltonian developed in this earlier work in which the torsional motion is grouped with the vibrational degrees of freedom, a good fit to within experimental error has been obtained by varying 45 parameters. A fit of comparable quality has also been obtained using a similar analysis in which the torsional motion is grouped with the rotational degrees of freedom. The values of the molecular constants determined in the two models are compared.     

New high-resolution analysis of the {ν1 + ν3} band of the NO2 isotopomer of nitrogen dioxide: Line positions and intensities

The high-resolution Fourier transform absorption spectrum of an isotopic sample of nitrogen dioxide, ¹⁵N¹⁶O₂, was recorded in the 3.4 μm region. Starting from the results of a previous study [Y. Hamada, J. Mol. Struct. 242 (1991) 367-377] a new analysis of the ν₁ + ν₃ band located at 2858.7077 cm⁻¹ has been performed. This new assignment concerns (1 0 1) energy levels involving rotational quantum numbers up to K_a = 10 and N = 54. Using a theoretical model which accounts for both the electron spin-rotation resonances within each vibrational state and the Coriolis interactions between the (1 2 0) and (1 0 1) vibrational states, the spin-rotation energy levels of the (1 0 1) vibrational state could be reproduced within their experimental uncertainty. In this way, the precise vibrational energy, rotational, spin-rotation, and coupling constants were achieved for the {(1 2 0), (1 0 1)} interacting states of ¹⁵N¹⁶O₂. Using these parameters and the transition moment operator which was obtained for the main isotopic species, ¹⁴N¹⁶O₂, a comprehensive list of the line positions and intensities was generated for the ν₁ + ν₃ band of ¹⁵N¹⁶O₂.     

Determination of the rate of H + O2 + M → HO2 + M (M = N2, Ar, H2O) from ignition of syngas at practical conditions

In H₂ and H₂/CO oxidation, the H + O₂ + M termination step is one of the most important reactions at elevated pressures. With the recent, increased interest in synthetic fuels, an accurate assessment of its rate coefficient becomes increasingly important, especially for real fuel/air mixtures. Ignition delay times in shock-tube experiments at the conditions selected in this study are only sensitive to the rates of the title reaction and the branching reaction H + O₂ = OH + O, the rate of which is known to a high level of accuracy. The rate coefficient of the title reaction for M = N₂, Ar, and H₂O was determined by adjusting its value in a detailed chemical kinetics model to match ignition delay times for H₂/CO/O₂/N₂, H₂/CO/O₂/Ar, and H₂/CO/O₂/N₂/H₂O mixtures with fuel/air equivalence ratios of ? = 0.5, 0.9, and 1.0. The rate of H + O₂ + N₂ = HO₂ + N₂ was measured to be 2.7 (−0.7/+0.8) × 10¹⁵ cm⁶/mol² s for T = 916-1265 K and P = 1-17 atm. The present determination agrees well with the recent study of Bates et al. [R.W. Bates, D.M. Golden, R.K. Hanson, C.T. Bowman, Phys. Chem. Chem. Phys. 3 (2001) 2337-2342], whose rate expressions are suggested herein for modeling the falloff regime. The rate of H + O₂ + Ar = HO₂ + Ar was measured to be 1.9 × 10¹⁵ cm⁶/mol² s for T = 932-965 K and P = 1.4 atm. The rate of H + O₂ + H₂O = HO₂ + H₂O was measured to be 3.3 × 10¹⁶ cm⁶/mol² s for T = 1071-1161 K and P = 1.3 atm. These are the first experimental measurements of the rates of the title reactions in practical combustion fuel/air mixtures.     

Quantum interference effects in a multi-driven transition Fg = 3 ↔ Fe = 2

We calculated and studied the quantum coherence effects of a degenerate transition F_g = 3 ↔ F_e = 2 system interacting with a weak linearly polarized (with σ_± components) probe light and a strong linearly polarized (with σ_± components) coupling field. Due to the competition between the drive Rabi frequency and the Zeeman splitting, electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA) are appeared at the different values of applied magnetic field in both cases that the Zeeman splitting of excited state Δe is smaller than the Zeeman splitting of ground state Δg (i.e., Δe < Δg) and Δe > Δg. It is shown that the resonance is broader and contrasts are higher for Δe < Δg than that for Δe > Δg at the same Rabi frequencies of probe and coupling fields.     

Global fit analysis including the ν9 + ν4 − ν4 hot band of ethane: Evidence of an interaction with the ν12 fundamental

The ν₉ fundamental band of ethane occurs in the 12 μm region. It is the strongest band of ethane in a terrestrial window and is commonly used for the identification of ethane in the Jovian planets. The ν₉ + ν₄ − ν₄ band occurs in the same region; neither can be analysed as an isolated band, since both are embedded in the torsional bath of the ground vibrational state. We report here two global fit models including data from both of these bands as well as the ν₃ fundamental and the ν₄, 2ν₄ − ν₄, and 3ν₄ torsional transitions. The first is restricted to −5 ? KΔK ? 15 in the hot band and gives an excellent fit to the included data. Three resonant interactions are identified in this fit—a Coriolis interaction with two resonant cases between the ν₉ torsional stack and that of the ground vibrational state (gs) and a resonant Fermi interaction between the ν₃ fundamental and the gs. Hot band lines with KΔK < −5 are influenced by a fourth perturbation, with a crossing at −11 < KΔK < −10, which has been attributed to an interaction with the ν₁₂ fundamental. A second fit, demonstrating a promising treatment of this interaction, is also presented.     

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.