The Rotational Spectrum of ClClO2 in Its v4=1 and v6=1 Vibrationally Excited States: An Example of Strong Coriolis Interaction

The two lowest vibrational states of ³⁵Cl³⁵ClO₂, v₄=1 (A′) and v₆=1 (A″), were investigated between 223 and 500 GHz. More than 250 rotational transitions were recorded with J and K_a up to 71 and 34, respectively. The spectra are heavily perturbed by strong c-type and weaker a-type Coriolis interactions. Near degeneracies of rotational levels of the two vibrational states having ΔJ=0, ΔK_a=5 to 1, and ΔK_a+ΔK_c= odd cause moderate to severe perturbations in the rotational structure, preventing the states from being fit as isolated ones. Distortions in the hyperfine structure facilitated the assignment of rotational quantum numbers. Several resonantly interacting levels with ΔK_a=5 to 2 were accessed, and a number of transitions between the states were observed. While resonant Coriolis interaction with ΔK_a=1 occurs only at K_a>40, the effects of this interaction are so severe that nonresonant interaction considerably perturbs the highest K_aQ-branches observed. The observed transitions could be fit to within experimental uncertainties employing the first-order Coriolis coupling constants fixed to those from the harmonic force field, sextic distortion constants fixed to those of the ground state, and some higher order Coriolis terms. The energy difference calculated from the fit agrees well with that obtained from the matrix-isolation infrared spectrum. Quadrupole coupling constants were determined for both Cl nuclei and both vibrational states.     

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.     

Experimental determination of pressure-broadening parameters of millimeter-wave transitions of HNO3 perturbed by N2 and O2, and of their temperature dependences

We report on linewidth measurements on the J=24_K,11−23_K^′,10 and J=38_K,33−37_K^′,32 millimeter wave transitions in the ground vibrational state of nitric acid, located near 470.23 and 544.36 GHz, respectively. Experiments were performed with N₂ and O₂ as perturber molecules, in the 240-350 K temperature range by using a video-type spectrometer. The foreign-gas broadening parameters and their temperature dependence coefficients were determined using the Voigt profile, no narrowing effect being observed. In order to check the reliability of reported values, we carried out measurements on the J=14_K,12−13_K^′,11 transition located near 206.6 GHz, previously observed in two other laboratories. For this last line all the reported values are consistent themselves within one claimed standard deviation.     

Self-broadening coefficients in the ν7 band of ethylene at room and low temperatures

Using a tunable diode-laser spectrometer, we have measured self-broadening coefficients for a few transitions in the ν₇ fundamental band of C₂H₄ at 298 and 174 K. The studied transitions J^′, K_a^′, K_c^′←J, K_a, K_c with 3?J?17, 1?K_a?4, and 1?K_c?14 are located in the spectral range 919-982 cm⁻¹. The collisional widths are measured by fitting each spectral line with Voigt, Rautian, and speed-dependent Rautian profiles. The latter model provides larger broadening coefficients than the Rautian profile and still larger coefficients than the Voigt profile. An approximate semiclassical calculation performed by considering only electrostatic interactions leads to reasonable agreement with the experimental data. By comparing the results obtained at room and low temperatures, the temperature dependence of the self-broadening has been determined both experimentally and theoretically.     

Measurements and theoretical calculations of N2-broadening and N2-shift coefficients in the ν2 band of CH3D

In this paper, we report measured Lorentz N₂-broadening and N₂-induced pressure-shift coefficients of CH₃D in the ν₂ fundamental band using a multispectrum fitting technique. These measurements were made by analyzing 11 laboratory absorption spectra recorded at 0.0056 cm⁻¹ resolution using the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory on Kitt Peak, Arizona. The spectra were obtained using two absorption cells with path lengths of 10.2 and 25 cm. The total sample pressures ranged from 0.98 to 402.25 Torr with CH₃D volume mixing ratios of 0.01 in nitrogen. We have been able to determine the N₂ pressure-broadening coefficients of 368 ν₂ transitions with quantum numbers as high as J″ = 20 and K = 16, where K″ = K′ ≡ K (for a parallel band). The measured N₂-broadening coefficients range from 0.0248 to 0.0742 cm⁻¹ atm⁻¹ at 296 K. All the measured pressure-shifts are negative. The reported N₂-induced pressure-shift coefficients vary from about −0.0003 to −0.0094 cm⁻¹ atm⁻¹. We have examined the dependence of the measured broadening and shift parameters on the J″, and K quantum numbers and also developed empirical expressions to describe the broadening coefficients in terms of m (m = −J″, J″, and J″ + 1 in the ^QP-, ^QQ-, and ^QR-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 4.7%. The N₂-broadening and pressure-shift coefficients were calculated on the basis of a semiclassical model of interacting linear molecules performed by considering in addition to the electrostatic contributions the atom-atom Lennard-Jones potential. The theoretical results of the broadening coefficients are in good overall agreement with the experimental data (8.7%). The N₂-pressure shifts whose vibrational contribution is derived from parameters fitted in the ^QQ-branch of self-induced shifts of CH₃D, are also in reasonable agreement with the scattered experimental data (20% in most cases).     

The ground state torsion-rotation spectrum of propargyl alcohol (HCCCH2OH)

The rotation-torsion spectrum of the asymmetric frame-asymmetric top internal rotor propargyl alcohol (HCCCH₂OH) has been extended into the millimeter and submillimeter wave spectral regions. Over 2000 ground torsional state transitions have been measured and analyzed up to rotational quantum numbers J = 80 and K_a = 33 through a frequency of 633 GHz. The newly measured transitions were added to approximately 200 previously reported and now unambiguously assigned microwave transitions to comprise a data set of 2390 transitions which has been fit to 59 kHz using a reduced axis method (RAM) Hamiltonian. The ground state has been confirmed to consist of a symmetric and an antisymmetric gauche conformer with no spectroscopic evidence of stable trans conformer. A complete set of rotation and distortion constants through 6th order and a number of the 8th and one 10th order constants for the normal species are presented along with those determined from a re-analysis of the existing OD species data. The a and b symmetry Coriolis interaction constants and the gauche+ gauche− tunnelling frequency of 652389.4 MHz has been determined for the OH species while the b symmetry Coriolis interaction and the 213 480 MHz tunnelling frequency were determined for the OD species.     

Measurements and theoretical calculations of self-broadening and self-shift coefficients in the ν2 band of CH3D

In this paper, we report measured Lorentz self-broadening and self-induced pressure-shift coefficients of ¹²CH₃D in the ν₂ fundamental band (ν₀ ≈ 2200 cm⁻¹). The multispectrum fitting technique allowed us to analyze simultaneously seven self-broadened absorption spectra. All spectra were recorded at the McMath-Pierce Fourier transform spectrometer of the National Solar Observatory (NSO) on Kitt Peak, AZ with an unapodized resolution of 0.0056 cm⁻¹. Low-pressure (0.98-2.95 Torr) as well as high-pressure (17.5-303 Torr) spectra of ¹²C-enriched CH₃D were recorded at room temperature to determine the pressure-broadening coefficients of 408 ν₂ transitions with quantum numbers as high as J″ = 21 and K = 18, where K″ = K′ ≡ K (for a parallel band). The measured self-broadening coefficients range from 0.0349 to 0.0896 cm⁻¹ atm⁻¹ at 296 K. All the measured pressure-shifts are negative. The reported pressure-induced self-shift coefficients vary from about −0.004 to −0.008 cm⁻¹ atm⁻¹. We have examined the dependence of the measured broadening and shift parameters on the J″, and K quantum numbers and also developed empirical expressions to describe the broadening coefficients in terms of m (m = −J″, J″, and J″ + 1 in the ^QP-, ^QQ-, and ^QR-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 3.6%. A semiclassical theory based upon the Robert-Bonamy formalism of interacting linear molecules has been used to calculate these self-broadening and self-induced pressure-shift coefficients. In addition to the electrostatic interactions involving the octopole and hexadecapole moments of CH₃D, the intermolecular potential includes also an atom-atom Lennard-Jones model. For low K (K ? 3) with |m| ? 8 the theoretical results of the broadening coefficients are in overall good agreement (3.0%) with the experimental data. For transitions with K approaching |m|, they are generally significantly underestimated (8.8%). The theoretical self-induced pressure shifts, whose vibrational contribution is derived from results in the ^QQ-branch, are generally smaller in magnitude than the experimental data in the ^QP-, and ^QR-branches (15.2%).     

Room-temperature broadening and pressure-shift coefficients in the ν2 band of CH3D-O2: Measurements and semi-classical calculations

We report measured Lorentz O₂-broadening and O₂-induced pressure-shift coefficients of CH₃D in the ν₂ fundamental band. Using a multispectrum fitting technique we have analyzed 11 laboratory absorption spectra recorded at 0.011 cm⁻¹ resolution using the McMath-Pierce Fourier transform spectrometer, Kitt Peak, Arizona. Two absorption cells with path lengths of 10.2 and 25 cm were used to record the spectra. The total sample pressures ranged from 0.98 to 339.85 Torr with CH₃D volume mixing ratios of 0.012 in oxygen. We report measurements for O₂ pressure-broadening coefficients of 320 ν₂ transitions with quantum numbers as high as J″ = 17 and K = 14, where K″ = K′ ≡ K (for a parallel band). The measured O₂-broadening coefficients range from 0.0153 to 0.0645 cm⁻¹ atm⁻¹ at 296 K. All the measured pressure-shifts are negative. The reported O₂-induced pressure-shift coefficients vary from about −0.0017 to −0.0068 cm⁻¹ atm⁻¹. We have examined the dependence of the measured broadening and shift parameters on the J″, and K quantum numbers and also developed empirical expressions to describe the broadening coefficients in terms of m (m = −J″, J″, and J″ + 1 in the ^QP-, ^QQ-, and ^QR-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 4.4%. The O₂-broadening and pressure shift coefficients were calculated on the basis of a semiclassical model of interacting linear molecules performed by considering in addition to the electrostatic contributions the atom-atom Lennard-Jones potential. The theoretical results of the broadening coefficients are generally larger than the experimental data. Using for the trajectory model an isotropic Lennard-Jones potential derived from molecular parameters instead of the spherical average of the atom-atom model, a better agreement is obtained with these data, especially for |m| ? 12 values (11.3% for the first calculation and 8.1% for the second calculation). The O₂-pressure shifts whose vibrational contribution are either derived from parameters fitted in the ^QQ-branch of self-induced shifts of CH₃D or those obtained from pressure shifts induced by Xe in the ν₃ band of CH₃D are in reasonable agreement with the scattered experimental data (17.0% for the first calculation and 18.7% for the second calculation).     

Rotational spectrum of the v11 = 1 and v14 = 1 vibrational states of CH3CCCCH

The pure rotational spectra of the v₁₁ = 1 and v₁₄ = 1 vibrational states of the main isotopic species of methyldiacetylene have been recorded and assigned in the 80-400 GHz frequency range, spanning the quantum numbers 19 ? J ? 95 and 0 ? K ? 15. The present study allows us to provide accurate rotational, centrifugal distortion and vibration-rotation interaction constants. The experimental investigation has been strongly supported by quantum-chemical computations at the second-order Møller-Plesset theory (MP2) in conjunction with a triple-zeta quality basis set.     

First high-resolution analysis of the 5ν3 band of nitrogen dioxide near 1.3 μm

The first high-resolution absorption spectrum of the 5ν₃ band of the ¹⁴N¹⁶O₂ molecule at 7766.071 cm^?1 was recorded by high sensitivity CW-Cavity Ring Down Spectroscopy between 7674 and 7795 cm^?1. The noise equivalent absorption of the recordings was α_min≈1×10^?10 cm^?1. The assignments involve energy levels of the (0,0,5) vibrational state with rotational quantum numbers up to K_a=9 and N=47. The set of the spin–rotation energy levels were reproduced within their experimental uncertainty using a theoretical model, which takes explicitly into account the Coriolis interactions between the spin rotational levels of the (0,0,5) vibrational state and those of the (0,2,4) dark state together with the electron spin–rotation resonances within the (0,0,5) and (0,2,4) states. Precise values were determined for the (0,0,5) vibrational energy rotational, spin-rotational constants and for the (0,2,4)?(0,0,5) coupling constants. In addition the (0,2,4) rotational and spin-rotational constants were estimated. Using these parameters and the value of the transition dipole moment operator determined from a fit of a selection of experimental line intensities, the synthetic spectrum of the 5ν₃ band was generated and is provided as Supplementary material.     

The interacting states (030), (110), and (011) of H216O

A fit of 382 rotational levels of the three vibrational states (030), (110), and (011) of H₂¹⁶O has been performed using 51 effective constants. The Fermi-type interaction between (030) and (110) and the Coriolis-type interaction between (110) and (011) as well as between (030) and (011) are taken into account. The part of the Hamiltonian which is diagonal in the vibrational quantum numbers is a Watson-type Hamiltonian. Considering the wide spread of J and K_a values, the general agreement between experimental and calculated levels is satisfactory. A comparison with the results relative to the states (020), (100), and (001) is given.     

Direct observation of the torsional fundamental of gaseous C2F6 in the far infrared

The forbidden a_1u torsional vibration of C₂F₆ has been observed in far-infrared absorption at 67.5 cm^?1 with an integrated intensity of 0.20 ± 0.08 × 10^?2 cm^?2. The observed intensity is compared with that expected theoretically from Coriolis coupling of the torsion to the infarred-active a_2u and e_u vibrations. For certain force fields and choices of sign for the dipole moment derivatives the agreement is satisfactory. The potential barrier to internal rotation has been recomputed from the observed torsional frequency to be 1367 cm^?1. (3.91 kcal mole^?1). This value is compared with those of ethane and partially fluorinated ethanes.     

Infrared and microwave high-resolution spectrum of the ν3 band of ozone

The vibration-rotation band ν₃ of ozone has been recorded with a high-resolution (0.012 cm^?1) spectrometer, and microwave absorption spectra of ozone have been identified in the excited vibrational states (100) and (001). A strong Coriolis interaction has been observed. More than 1200 spectral lines have been identified in the ν₃ band, using a Watson-type Hamiltonian, including all the sextic centrifugal distortion terms. Band constants and an atlas listing line wavenumbers, intensities, and assignments are given, from 1007 to 1072 cm^?1. It is shown that transitions with high values of the quantum numbers K_?1 (≥11) contribute to significant absorption.     

Rotation-torsion-vibration term-value mapping for CH3OH: Torsion-mediated doorways and corridors for intermode population transfer

Fourier transform infrared spectra of CH₃OH from 930-1650 cm⁻¹ have been analyzed to reveal details of the rotation-torsion-vibration energy manifold of the CO-stretching, CH₃-rocking, OH-bending and CH₃-deformation modes and their torsional combination states. Mapping of the upper-state term values as a function of the rotational quantum number J has shown the locations of numerous substate crossing resonances that give rise to J-localized spectral perturbations and substate mixing and thereby create “doorways” for collision-induced population transfer among the different modes. Other near-degenerate substates are more globally mixed over a wide range of J, corresponding to “corridors” of doorways. Where both partner substates in a doorway resonance have been identified, the perturbations have been analyzed to find estimates of the interaction matrix elements and the degree of mixing between the coupled states. Many of the resonances are between substates of differing torsional quantum number, highlighting the importance of torsion in generating the doorway channels and enhancing intermode vibrational population transfer.     

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.     

Laser-induced fluorescence of Pb2

Pb₂, which occurs in lead vapor, was studied by the technique of laser-induced fluorescence using single-mode Ar-laser excitation. The fluorescence observed could be classified into the F-X system. Ten progressions involving vibrational quantum numbers v′ = 0?9 and v″ = 0?22 were analyzed. Including collision-induced lines, rotational quantum numbers from J = 25 to J = 300 were observed. The vibrational constants and the numbering of the states had to be reassigned. For the first time rotational constants were determined for the Pb₂ molecule. The internuclear distances of ²⁰⁸Pb₂ in the F and X state are $\text{r = 3.079}\text{A}\text{?}$ and $\text{r}{}_{\mathrm{<mtext>e</mtext>}}\text{= 2.930}\text{A}\text{?}$, respectively. Using the constants derived RKR potentials and Franck-Condon factors were calculated, which confirmed the vibrational assignments and constants.     

The ν2 fundamental band of H2CO

The ν₂ fundamental band of H₂CO has been studied using a combination of sub-Doppler laser Stark spectroscopy and Doppler-limited Fourier transform spectroscopy. A combined analysis of the Stark and Fourier infrared data together with previous microwave data on the ν₂ = 1 state yielded improved molecular parameters for formaldehyde, including the excited state dipole moment. A small perturbation was noted at K′_a = 7 which may be ascribed to a ΔK_a = 2 interaction with the v₃ = 1 state. Precise treatments of ν₂ with K′_a > 6 will thus require a combined analysis taking into account Coriolis interactions among ν₄, ν₆, ν₃, and ν₂.     

High-resolution FTIR measurement of the 2ν8 band of methylene fluoride (CH2F2)

A high-resolution (0.003 cm⁻¹) infrared absorption spectrum of the first overtone of the fundamental mode ν₈ of methylene fluoride (CH₂F₂) has been measured on a Bruker IFS 120-HR Fourier transform infrared spectrometer. More than 2000 ro-vibration transitions in the range of 2770-2900 cm⁻¹ with J ? 45 and K_a ? 20 have been assigned in this B-type band centered at 2838.5 cm⁻¹. Precise value for the band origin (2838.579799 cm⁻¹) and centrifugal distortion constants up to third order (Φ_JK, Φ_KJ, and Φ_K) have been obtained by fitting a total of 1474 unblended ro-vibration transitions (J ? 45 and K_a ? 13) of the 2ν₈ band with a standard deviation of 0.00029 cm⁻¹ using a Watson’s A-reduced Hamiltonian in the I^r representation. Signature of perturbations with nearby states has been seen.     

Variationally exact ro-vibrational levels of the floppy CH2+ molecule

Ro-vibrational calculations are performed on the CH₂⁺ radical using a method recently developed for atom-diatom systems. The vibrational fundamentals obtained are 2998.8, 718.3, and 3270.7 cm^?1, in good agreement with recent results. Band origins for several higher vibrational levels are also obtained. Calculations with J = 1 show that the Coriolis interaction play a significant role and two alternative embeddings are discussed. Use of correlation parameters confirms that CH₂⁺ belongs to no idealized class of molecules in keeping with its “floppy” nature.     

The fundamental band ν2 of D2CO

The ν₂ band of D₂¹³CO in the region of 1570-1760 cm⁻¹ has been analyzed with high accuracy. The limits of the quantum numbers J and K_a are 50 and 16, respectively. The number of the assigned transitions is 3858. A local anharmonic resonance ν₂/2ν₄ at K_a =  8-12 was observed. The Watson’s A-reduced Hamiltonian and anharmonic resonance term were fitted to the observed transitions. The fit resulted in the band center and rotational parameters of the ν₂ band as well as the effective parameters for the 2ν₄ band and anharmonic resonance parameter. The rms deviation of the transitions in the ν₂ band was 0.000364 cm⁻¹.