The high-resolution infrared spectrum of pyrrole between 900 and 1500 cm revisited

The Fourier transform gas-phase infrared spectrum of pyrrole, C₄H₅N, has been recorded with a resolution of ca. 0.003 cm⁻¹ in the 900-1500 cm⁻¹ spectral region. Four fundamental bands, ν₈(A₁; 1016.9 cm⁻¹), ν₂₃(B₂; 1049.1 cm⁻¹), ν₇(A₁; 1074.6 cm⁻¹), ν₂₀(B₂; 1424.4 cm⁻¹) and the overtone band 2ν₁₆(A₁; 962.7 cm⁻¹) have been analysed using the Watson model. The ν₈ and 2ν₁₆ bands are unperturbed; the ν₇ and ν₂₃ bands are locally perturbed, while the ν₂₀ band is globally perturbed by weak c-Coriolis resonance. Upper state vibrational term values, and rotational and centrifugal distortion constants, have been obtained from fits using S-reduction and I^r-representation as well as A-reduction and III^r-representation. A set of ground state rotational and centrifugal distortion constants using A-reduction was obtained from a simultaneous fit of ground state combination differences from all five bands and previous microwave and millimetre-wave data.     

Characterization of MeWO4 (Me = Ba, Sr and Ca) nanocrystallines prepared by sonochemical method

Metal tungstates (MeWO₄, Me = Ba, Sr and Ca) were successfully prepared using the corresponding Me(NO₃)₂·2H₂O and Na₂WO₄·2H₂O in ethylene glycol by the 5 h sonochemical process. The tungstate phases with scheelite structure were detected with X-ray diffraction (XRD) and selected area electron diffraction (SAED). Their calculated lattice parameters are in accord with those of the JCPDS cards. Transmission electron microscopy (TEM) revealed the presence of nanoparticles composing the products. Their average sizes are 42.0 ± 10.4, 18.5 ± 5.1 and 13.1 ± 3.3 nm for Me = Ba, Sr and Ca, respectively. Interplanar spaces of the crystals were also characterized with high-resolution TEM (HRTEM). Their crystallographic planes are aligned in systematic array. Six different vibration wavenumbers were detected using Raman spectrometer and are specified as ν₁(A_g), ν₃(B_g), ν₃(E_g), ν₄(B_g), ν₂(A_g) and free rotation. Fourier transform infrared (FTIR) spectra provided the evidence of scheelite structure with W-O anti-symmetric stretching vibration of [WO₄]²⁻ tetrahedrons at 786-883 cm⁻¹. Photoluminescence emission of the products was detected over the range of 384-416 nm.     

High-resolution infrared and theoretical study of the fundamental bands ν6, ν7, ν9 and ν13 of 1,2,3-thiadiazole

The Fourier transform gas-phase IR spectrum of 1,2,3-thiadiazole, C₂H₂N₂S, has been recorded with a resolution of ca. 0.003 cm⁻¹ in the 700-1100 cm⁻¹ spectral region. Four fundamental bands ν₆(A^/; 1101.8 cm⁻¹), ν₇(A^/; 1038.8 cm⁻¹), ν₉(A^/, 858.9 cm⁻¹), and ν₁₃(A^//; 746.2 cm⁻¹) have been analyzed using the Watson model in A-reduction. Two additional bands, ν₈ (A^/; 894.6 cm⁻¹) and ν₁₂(A^//; 881.2 cm⁻¹) were assigned by their weak Q-branches. Ground state rotational and quartic centrifugal distortion constants as well as upper state spectroscopic constants have been obtained from fits. A number of weak global and local interactions are present in the bands. The resonances identified were qualitatively explained by Coriolis type perturbations with neighboring levels. Ground state rotational and quartic centrifugal distortion constants, anharmonic frequencies, and vibration-rotational α-constants predicted by quantum chemical calculations using a cc-pVTZ basis and B3LYP methodology, have been compared with the present experimental data, where there is generally good agreement.     

A high-resolution infrared study of five bands of 1,2,5-thiadiazole in the range 750-1250 cm, together with ab initio and DFT studies

The Fourier transform gas-phase IR spectrum of 1,2,5-thiadiazole, C₂H₂N₂S, has been recorded with a resolution of ca. 0.003 cm⁻¹ in the wavenumber region 750-1250 cm⁻¹. Five fundamental bands in this region, ν₄ (A₁), ν₅ (A₁), ν₁₁ (B₁), ν₁₃ (B₁), and ν₁₄ (B₂), have been analysed by the Watson Hamiltonian model to yield ground-state rotational and quartic centrifugal distortion constants as well as upper-state spectroscopic constants. A global perturbation of the ν₄ level is explained by Fermi resonance with the 2ν₁₅ level which has been located from its resonance effect. Rotational constants, harmonic and anharmonic frequencies have been calculated using a cc-pVTZ basis, at the MP2 and B3LYP methodology levels, and compared with the experimental data.     

High-resolution infrared and theoretical study of the fundamental bands ν2, ν4 and ν9 and the c-Coriolis interacting dyad ν5, ν14 of 1,3,4-thiadiazole

The Fourier transform gas-phase IR spectrum of 1,3,4-thiadiazole, C₂H₂N₂S, has been recorded with a resolution of ca. 0.003 cm⁻¹ in the 800-1500 cm⁻¹ spectral region. Five fundamental bands ν₂(A₁; 1391.9 cm⁻¹), ν₄(A₁; 964.4 cm⁻¹), ν₅(A₁; 894.6 cm⁻¹), ν₉(B₁; 821.5 cm⁻¹), and ν₁₄(B₂; 898.4 cm⁻¹) have been analysed using the Watson model. Ground state rotational and quartic centrifugal distortion constants as well as upper state spectroscopic constants have been obtained from fits. The ν₄ and ν₉ bands are unperturbed while a strong c-Coriolis resonance perturbs the close-lying ν₅ and ν₁₄ bands. This dyad system has been analysed by a model including first and second order c-Coriolis resonance using the theoretically predicted Coriolis coupling constant . The ν₂ band is strongly perturbed by a local resonance, and we obtain a set of spectroscopic parameters using a model including second order a-Coriolis resonance with the inactive ν₁₀ + ν₁₄ band. Ground state rotational and quartic centrifugal distortion constants, anharmonic frequencies, and vibration-rotational α-constants predicted by quantum chemical calculations using a cc-pVTZ basis and B3LYP methodology, have been compared with the present experimental data, where there is generally good agreement.     

The absorption spectrum of phosphine (PH3) between 2.8 and 3.7 μm: Line positions, intensities, and assignments

Over 8000 line positions and intensities of phosphine (PH₃) at 3 μm have been measured at 0.0115 cm⁻¹ resolution with the McMath-Pierce Fourier Transform spectrometer at Kitt Peak. The observed line intensities ranged from 4.13 × 10⁻⁶ to 4.69 × 10⁻² cm⁻² atm⁻¹ at 296 K, for line positions between 2724.477 and 3601.652 cm⁻¹. This region spans eight interacting vibrational states: 3ν₂ (2940.8 cm⁻¹), 2ν₂ + ν₄ (3085.6 cm⁻¹), ν₂ + 2ν₄ (3214.9 cm⁻¹), ν₁ + ν₂ (3307.6 cm⁻¹), ν₂ + ν₃ (3310.5 cm⁻¹), 3ν₄ (∼3345 cm⁻¹), ν₁ + ν₄ (3426.9 cm⁻¹), and ν₃ + ν₄ (3432.9 cm⁻¹). Assignments have been determined for all the bands except 3ν₄ (a weak band in a highly congested area) for a total of 4232 transitions. The total integrated intensity for this region is 5.70 cm⁻² atm⁻¹ near 296 K, and assigned lines account for 79% of the observed absorption. The two strongest bands in the region are ν₁ + ν₄ and ν₃ + ν₄ with band strengths at 296 K of 1.61 and 2.01 cm⁻² atm⁻¹, respectively. An empirical database of PH₃ line parameters (positions, intensities, and assignments) is now available. Lower state energies (corresponding to assignments from this study) and line widths from the literature are included; default values are used for unassigned features.     

High-resolution infrared and theoretical study of gaseous 1,2,5-selenadiazole in the 600-1400 cm range

The Fourier transform gas-phase IR spectrum of natural isotopic 1,2,5-selenadiazole, C₂H₂N₂Se, has been recorded with a resolution of ca. 0.0025 cm⁻¹ in the wavenumber region 600-1400 cm⁻¹. The three a-type bands, ν₂ (A₁), ν₄ (A₁), ν₅ (A₁), the two b-type bands ν₁₁ (B₁), ν₁₂ (B₁), and the c-type band ν₁₄ (B₂) for each of the isotopologues C₂H₂N₂⁸⁰Se and C₂H₂N₂⁷⁸Se have been analyzed using the Watson model. Ground state rotational and quartic centrifugal distortion constants as well as upper state spectroscopic constants have been obtained from the fits. The rotational constants, harmonic and anharmonic frequencies, and vibration-rotation constants (alphas, ) have been predicted by quantum chemical calculations using a cc-pVTZ basis at the MP2 and B3LYP methodology levels, and compared with the present experimental data. Although the rotation constants are marginally closer to experiment from the MP2 calculations, in general the B3LYP frequencies and alphas are closer to experiment.     

CW-cavity ring down spectroscopy of the ozone molecule in the 6625-6830 cm region

The absorption spectrum of ozone, ¹⁶O₃, has been recorded by CW-cavity ring down spectroscopy in the 6625-6830 cm⁻¹ region. The typical sensitivity of these recordings (α_min ∼ 3 × 10⁻¹⁰ cm⁻¹) allows observing very weak transitions with intensity down to 2 × 10⁻²⁸ cm/molecule. 483 and 299 transitions have been assigned to the 2ν₁ + 3ν₂ + 3ν₃A-type band and to the 2ν₁ + 4ν₂ + 2ν₃B-type band, respectively, which are the highest frequency bands of ozone recorded so far under high resolution. Rovibrational transitions with J and K_a values up to 46 and 12, respectively, could be assigned. Despite well-known difficulties to correctly reproduce the energy levels not far from the dissociation limit, it was possible to determine the parameters of an effective Hamiltonian which includes six vibrational states, four of them being dark states. The line positions analysis led to an rms deviation of 8.5 × 10⁻³ cm⁻¹ while the experimental line intensities could be satisfactorily reproduced. Additional experiments in the 5970-6021 cm⁻¹ region allows detecting the (233) ← (010) hot band reaching the same upper state as the preceding cold band. From the effective parameters of the (233) state just determined and those of the (010) level available in the literature, 329 transitions could be assigned and used for a further refinement of the rovibrational parameters of the effective Hamiltonian leading to a value of 7.6 × 10⁻³ cm⁻¹ for the global rms deviation. The complete list of the experimentally determined rovibrational energy levels of the (233), (242), and (520) states is given. The determined effective Hamiltonian and transition moment operators allowed calculating a line list (intensity cut off of 10⁻²⁸ cm/molecule at 296 K), available as Supplementary material for the 6590-6860 and 5916-6021 cm⁻¹ regions. The integrated band strength values are 1.75 × 10⁻²⁴ and 4.78 × 10⁻²⁵ cm/molecule at 296 K for the 2ν₁ + 3ν₂ + 3ν₃A-type band and to the 2ν₁ + 4ν₂ + 2ν₃B-type band, respectively, while the band intensity value of the (233) ← (010) is estimated to be 1.03 × 10⁻²⁴ cm/molecule.     

The vibrational spectrum of thiazole between 600 and 1400 cm revisited: A combined high-resolution infrared and theoretical study

The Fourier transform infrared gas-phase spectrum of thiazole, C₃H₃NS, has been recorded in the 600-1400 cm⁻¹ wavenumber region with a resolution around 0.0030 cm⁻¹. Nine fundamental bands (ν₅(A′) to ν₁₁(A′), ν₁₅(A″), and ν₁₆(A″)) are analysed employing the Watson model. Ground-state rotational and quartic centrifugal distortion constants as well as upper state spectroscopic constants have been obtained from the fits. A detailed analysis of perturbations identified in the ν₁₁(A′) band at 866.5 cm⁻¹ enables a definitive location of the very weak ν₁₀(A′) and ν₁₄(A″) bands at 879.3 and 888.7 cm⁻¹, respectively. The three levels are analysed simultaneously by a model including Coriolis resonance using an ab initio predicted first order c-Coriolis coupling constant; second and higher order Coriolis parameters are determined. Qualitative explanations in terms of Coriolis resonances are given for a number of crossings observed in ν₅(A′), ν₆(A′), and ν₇(A′) at 1383.7, 1325.8, and 1240.5 cm⁻¹, respectively. The rotational constants, anharmonic frequencies, and vibration-rotation constants (alphas, ) calculated by quantum chemical calculations using a cc-pVTZ and TZ2P basis with B3LYP methodology, have been compared with the present experimental data. The rotation constant differences for each vibrational state, from the ground state values, are closer to experiment from the TZ2P calculations relative to those using cc-pVTZ. The values for Δ_J, Δ_JK, Δ_K, δ_J, and δ_K are close to experiment with both basis sets.     

The stretching fundamental bands ν1, ν2 and ν4 of HSiD3

The ν₁(A₁), Si-H stretching, ν₂(A₁) and ν₄(E), Si-D stretchings, fundamental bands of HSiD₃ have been recorded at an effective resolution of ca. 0.003 cm⁻¹ between 2080 and 2280 cm⁻¹ and between 1480 and 1720 cm⁻¹, respectively. Ro-vibrational transitions of the H²⁸SiD₃ isotopologue have been assigned in the two spectral ranges, about 700 belonging to ν₁, with J′ up to 25 and K up to 21, and about 1600 to the ν₂/ν₄ dyad, with J′ up to 24 and K′ up to 19. The spectra of all the bands evidence the existence of several perturbations. The transitions of ν₁ have been analyzed either neglecting or including in the model A₁/E Coriolis-type interactions with nearby dark states. The υ₂ = 1 and υ₄ = 1 states have been fitted simultaneously taking into account several ro-vibrational interactions between them and, in addition, with the υ₅ = 2, l = 0 component, and with few other close dark states. The standard deviation of the fit for both ν₁ and the ν₂/ν₄ dyad is, however, more than one order of magnitude larger than the estimated experimental precision and is independent on the adopted model.     

Analysis of some combination-overtone infrared bands of SO3

Several new infrared absorption bands for ³²S¹⁶O₃ have been measured and analyzed. The principal bands observed were ν₁+ν₂ (at 1561 cm⁻¹), ν₁+ν₄ (at 1594 cm⁻¹), ν₃+ν₄ (at 1918 cm⁻¹), and 3ν₃ (at 4136 cm⁻¹). Except for 3ν₃, these bands are very complicated because of (a) the Coriolis coupling between ν₂ and ν₄, (b) the Fermi resonance between ν₁ and 2ν₄, (c) the Fermi resonance between ν₁ and 2ν₂, (d) ordinary l-type resonance that couples levels that differ by 2 in both the k and l quantum numbers, and (e) the vibrational l-type resonance between the A₁^′ and A₂^′ levels of ν₃+ν₄. The unraveling of the complex pattern of these bands was facilitated by a systematic approach to the understanding of the various interactions. Fortunately, previous work on the fundamentals permitted good estimates of many constants necessary to begin the assignments and the fit of the measurements. In addition, the use of hot band transitions accompanying the ν₃ band was an essential aid in fitting the ν₃+ν₄ transitions since these could be directly observed for only one of four interacting states. From the hot band analysis we find that the A₁^′ vibrational level is 3.50 cm⁻¹ above the A₂^′ level, i.e., r₃₄=1.75236(7) cm⁻¹. In the case of the 3ν₃ band, the spectral analysis is straightforward and a weak Δk=±2, Δl₃=±2 interaction between the l₃=1 and l₃=3 substates locates the latter A₁^′ and A₂^′ “ghost” states 22.55(4) cm⁻¹ higher than the infrared accessible l₃=1 E^′ state.     

Joint ro-vibrational analysis of the HDS high resolution infrared data

High resolution Fourier transform spectra of the HDS molecule were recorded and analyzed for the first time in the region of the bands ν₁ + 2ν₂ (3938.6 cm⁻¹), ν₁ + ν₃ (4522.6 cm⁻¹), 2ν₂ + ν₃ (4638.8 cm⁻¹), 2ν₁ + ν₂ (4767.7 cm⁻¹), ν₁ + ν₂ + ν₃ (5525.2 cm⁻¹), 3ν₁ (5560.6 cm⁻¹), ν₁ + 2ν₃ (7047.2 cm⁻¹), and 2ν₂ + 2ν₃ (7123.9 cm⁻¹). The ro-vibrational energies of the upper vibrational states of these bands together with the ro-vibrational energies of 12 other bands already studied at high resolution were used as inputs in a Global Fit analysis firstly described in [O.N. Ulenikov, G.A. Onopenko, H. Lin, J.-H. Zhang, Z.-Y. Zhou, Q.-S. Zhu, R.N. Tolchenov, J. Mol. Spectrosc. 189 (1998) 29-39]. In this case, the resonance interactions between the states (v₁v₂v₃) and (v₁ ± 2 v₂ ? 1 v₃ ? 1) were taken into account. The resulting set of 143 parameters reproduces all the experimental data (2984 vibration-rotation energies of 20 vibrational states which correspond to about 9700 ro-vibrational transitions with J^max = 23) with accuracies comparable with the experimental uncertainties.     

The high-resolution infrared spectrum of thiophene between 600 and 1200 cm: A spectroscopic and theoretical study of the fundamental bands ν6, ν7, ν13, and the c-Coriolis interacting dyad ν5, ν19

The Fourier transform infrared spectrum of gaseous thiophene, C₄H₄S, has been recorded in the 600-1200 cm⁻¹ spectral region with a resolution of ca. 0.0030 cm⁻¹. Five fundamental bands ν₁₃ (B₁, 712.1 cm⁻¹), ν₇ (A₁; 840.0 cm⁻¹), ν₆ (A₁; 1036.4 cm⁻¹), ν₅ (A₁; 1081.5 cm⁻¹) and ν₁₉ (B₂; 1084.0 cm⁻¹) have been analysed by the standard Watson model (A-reduction). Ground state rotational and quartic centrifugal distortion constants have been obtained from a simultaneous fit of ground state combination differences from four of these bands and previous microwave transitions. Upper state spectroscopic constants have been obtained for all five bands from single band fits using the Watson model. A strong c-Coriolis resonance perturbs the close lying ν₅ and ν₁₉ bands. We have analysed this dyad system by a model including first and second order Coriolis resonance using the theoretically predicted Coriolis coupling constant . From this analysis we locate the previously unobserved ν₁₉ band at 1083.969 cm⁻¹. The rotational constants, ground state quartic centrifugal distortion constants, anharmonic frequencies, and vibration-rotational constants (α-constants) predicted by quantum chemical calculations using a cc-pVTZ basis with B3LYP methodology, are compared with the present experimental data, where there is generally good agreement. A complete set of anharmonic frequencies and α-constants for all fundamental levels of the molecule is given.     

High-resolution infrared spectra of bicyclo[1.1.1]pentane

Infrared spectra of bicyclo[1.1.1]pentane (C₅H₈) have been recorded at a resolution (0.0015 cm⁻¹) sufficient to resolve for the first time individual rovibrational lines. This initial report presents the ground state constants for this molecule determined from the detailed analysis of three of the ten infrared-allowed bands, ν₁₄(e′) at 540 cm⁻¹, ν₁₇ (a₂″) at 1220 cm⁻¹, ν₁₈(a₂″) at 832 cm⁻¹, and a partial analysis of the ν₁₁(e′) band at 1237 cm⁻¹. The upper states of transitions involving the lowest frequency mode, ν₁₄(e′), show no evidence of rovibrational perturbations but those for the ν₁₇ and ν₁₈ (a₂″) modes give clear indication of Coriolis coupling to nearby e′ levels. Accordingly, ground state constants were determined by use of the combination-difference method for all three bands. The assigned frequencies provided over 3300 consistent ground state difference values, yielding the following constants for the ground state (in units of cm⁻¹): B₀ = 0.2399412(2), D_J = 6.024(6) × 10⁻⁸, D_JK = −1.930(21) × 10⁻⁸. For the unperturbed ν₁₄(e′) fundamental, more than 3500 transitions were analyzed and the band origin was found to be at 540.34225(2) cm⁻¹. The numbers in parentheses are the uncertainties (two standard deviations) in the values of the constants. The results are compared with those obtained previously for [1.1.1]propellane and with those computed at the ab initio anharmonic level using the B3LYP density functional method with a cc-pVTZ basis set.     

High resolution analysis of the ethylene-1-C spectrum in the 8.4-14.3-μm region

Fourier transform spectra of mono-¹³C ethylene have been recorded in the 8.4-14.3-μm spectral region (700-1190 cm⁻¹) using a Bruker 120 HR interferometer at a resolution of 0.0017 cm⁻¹ allowing the extensive study of the set of resonating states {10¹, 8¹, 7¹, 4¹, 6¹}. Due to the high resolution available as well as the extended spectral range involved in this study, a much larger set of line assignments are now available. The present analysis has lead to the determination of more accurate spectroscopic constants, including interaction constants, than were obtained in earlier studies. In particular, the following band centers were derived: ν₀(ν₁₀) = 825.40602(30) cm⁻¹, ν₀(ν₈) = 932.19572(15) cm⁻¹, ν₀(ν₇) = 937.44452(10) cm⁻¹, ν₀(ν₄) = 1025.6976(14) cm⁻¹. Finally a synthetic spectrum was generated leading to the assignment of a number of ¹³C¹²CH₄ lines observed in an earlier heterodyne spectroscopic study.     

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.     

The high-resolution infrared spectrum of isoxazole vapor between 800 and 1700 cm

The Fourier transform gas-phase IR spectrum of isoxazole, C₃H₃NO, between 550 and 1700 cm⁻¹ was measured with a resolution of ca. 0.003 cm⁻¹. Ten fundamental bands in the region 800-1700 cm⁻¹ have been analyzed by the Watson Hamiltonian model to yield upper state spectroscopic constants. A number of local resonances have been identified in the bands and explained qualitatively, and the unobserved ν₁₄(A″) fundamental band has been located at 897.5(5) cm⁻¹ from its perturbation effects on the neighboring fundamentals.     

Preliminary analysis of CH3D from 3250 to 3700 cm

The infrared spectrum of CH₃D from 3250 to 3700 cm⁻¹ was studied for the first time to assign transitions involving the ν₂ + ν₃, ν₂ + ν₅, ν₂ + ν₆, ν₃ + 2ν₆ and 3ν₆ vibrational states. Line positions and intensities were measured at 0.011 cm⁻¹ resolution using Fourier transform spectra recorded at Kitt Peak with isotopically enriched samples. Some 2852 line positions (involving over 900 upper state levels) and 874 line intensities were reproduced with RMS values of 0.0009 cm⁻¹ and 4.6%, respectively. The strongest bands were found to be ν₂ + ν₃ at 3499.7 cm⁻¹ and ν₂ + ν₆ at 3342.5 cm⁻¹ with integrated strengths, respectively, of 8.17 × 10⁻²⁰ and 2.44 × 10⁻²⁰ (cm⁻¹/molecule · cm⁻²) at 296 K (for 100% CH₃D). The effective Hamiltonian was expressed in terms of irreducible tensor operators and adapted to symmetric top molecules. Its present configuration in the MIRS package permitted simultaneous consideration of the four lowest polyads of CH₃D: the Ground State (G.S.), the Triad from 6.3 to 9.5 μm, the Nonad from 3.1 to 4.8 μm and now the Enneadecad (19 bands) from 2.2 to 3.1 μm. The CH₃D line parameters for this interval were calculated to create a new database for the 3 μm region.     

Single crystal EPR and optical absorption study of Cr doped l-histidine hydrochloride monohydrate

EPR study of the Cr³⁺ ion doped l-histidine hydrochloride monohydrate single crystal is done at room temperature. Two magnetically inequivalent interstitial sites are observed. The hyperfine structure for Cr⁵³ isotope is also obtained. The zero field and spin Hamiltonian parameters are evaluated from the resonance lines obtained at different angular rotations and the parameters are: D=(300±2)×10⁻⁴ cm⁻¹, E=(96±2)×10⁻⁴ cm⁻¹, g_x=1.9108±0.0002, g_y=1.9791±0.0002, g_z=2.0389±0.0002, A_x=(252±2)×10⁻⁴ cm⁻¹, A_y=(254±2)×10⁻⁴ cm⁻¹, A_z=(304±2)×10⁻⁴ cm⁻¹ for site I and D=(300±2)×10⁻⁴ cm⁻¹, E=(96±2)×10⁻⁴ cm⁻¹, g_x=1.8543±0.0002, g_y=1.9897±0.0002, g_z=2.0793±0.0002, A_x=(251±2)×10⁻⁴ cm⁻¹, A_y=(257±2)×10⁻⁴ cm⁻¹, A_z=(309±2)×10⁻⁴ cm⁻¹ for site II, respectively. The optical absorption studies of single crystals are also carried out at room temperature in the wavelength range 195-925 nm. Using EPR and optical data, different bonding parameters are calculated and the nature of bonding in the crystal is discussed. The values of Racah parameters (B and C), crystal field parameter (Dq) and nephelauxetic parameters (h and k) are: B=636, C=3123, Dq=2039 cm⁻¹, h=1.46 and k=0.21, respectively.     

SO2: High-resolution analysis of the (0 3 0), (1 0 1), (1 1 1), (0 0 2) and (2 0 1) vibrational states; determination of equilibrium rotational constants for sulfur dioxide and anharmonic vibrational constants

High resolution Fourier transform spectra of a sample of sulfur dioxide, enriched in ³⁴S (95.3%). were completely analyzed leading to a large set of assigned lines. The experimental levels derived from this set of transitions were fit to within their experimental uncertainties using Watson-type Hamiltonians. Precise band centers, rotational and centrifugal distortion constants were determined. The following band centers in cm⁻¹ were obtained: ν₀(3ν₂)=1538.720198(11), ν₀(ν₁ + ν₃)=2475.828004(29), ν₀(ν₁ + ν₂ + ν₃)=2982.118600(20), ν₀(2ν₃)=2679.800919(35), and ν₀(2ν₁ + ν₃)=3598.773915(38). The rotational constants obtained in this work have been fit together with the rotational constants of lower-lying vibrational states [W.J. Lafferty, J.-M. Flaud, R.L. Sams, EL Hadjiabib, J. Mol. Spectrosc. 252 (2008) 72-76] to obtain equilibrium constants as well as vibration-rotation constants. These equilibrium constants have been fit together with those of ³²S¹⁶O₂ [J.-M. Flaud, W.J. Lafferty, J. Mol. Spectrosc. 16 (1993) 396-402] leading to an improved equilibrium structure. Finally the observed band centers have been fit to obtain anharmonic rotational constants.