ABSTRACT
New millimeter-wave and microwave measurements for CH(3)OD have been combined with previous literature data and with an extended body of Fourier transform far-infrared observations in a full global analysis of the first two torsional states (v(t) = 0 and 1) of the ground vibrational state. The fitted CH(3)OD data set contained 564 microwave and millimeter-wave lines and 4664 far-infrared lines, representing the most recent available information in the quantum number ranges J
ABSTRACT
The 3nu(2) overtone band of deuterium oxide, D(2)O, centered at 3474.3193 cm(-1), has been measured with high resolution in a 4-m base-length White cell attached to a Fourier transform spectrometer. The analysis of the spectrum led to the assignment of 347 transitions in this band, defining rovibrational energy levels in the (030) state up to K(a) = 7 for J as high as 9, and lower K(a) levels for J as high as 16. The (030) state was treated as an isolated state, following a Padé-Borel approximation in the effective Hamiltonian. Of the 115 energy levels included in the analysis, 80% were reproduced by the 21 adjusted parameters to within 0.0008 cm(-1), and the largest error was 0.0017 cm(-1). Copyright 2000 Academic Press.
ABSTRACT
The "Ritz" program, originally written for the analysis of the Fourier transform spectra of the methanol isotopomers and presented in previous papers, has been extended in order to analyze the spectra of other molecules. This program evaluates the term values involved in the assigned transitions by the Rydberg-Ritz combination principle, and can tackle such perturbations as Fermi-type resonances or Coriolis interactions. As a first application of the extended version, we present an investigation of the Fourier transform spectrum of cyanamide between 25 and 980 cm-1. More than 16 000 lines have been assigned. Our Ritz database now comprises a list of more than 19 000 assigned lines (including of the microwave and FIR lines available in the JPL database) and more than 3900 term values. All of the lines presented in this paper correspond to transitions within the ground and first excited inversion levels of the ground vibrational state of the small-amplitude modes. Copyright 1998 Academic Press.
ABSTRACT
This paper presents a high-resolution Fourier transform infrared study of the first CO-stretch overtone band of 13CH3OH. The spectrum has been recorded at the Justus-Liebig University, Gießsen, Germany on their Bruker IFS 120 HR Fourier transform spectrometer. We have assigned parallel subbands in the torsional state n = 0 for K values up to 6. Each individual subband has been fitted to a J(J + 1) power series expansion in order to obtain the subband origin and the state-specific energy expansion coefficients for the first CO-stretch overtone state. The average rotational constant B in the CO-stretch vCO = 2 state was found to be 0.768 cm-1, forming a smooth series with that of 0.777 cm-1 obtained in the vCO = 1 state and the ground state value of 0.787 cm-1. Modeling of the excited state torsion-vibration energy level structure derived from the subband origins is then discussed and molecular parameters in the vCO = 2 state are proposed. The value obtained for the barrier height to internal rotation is 377.06 +/- 0.52 cm-1, nearly indistinguishable from the value 378.65 cm-1 reported for the CO-stretch vCO = 1 state. The vibrational energy is found to be 2020.9 +/- 1.4 cm-1. The harmonic wavenumber for the CO-stretch vibration in 13CH3OH was calculated to be omega = 1029.9 cm-1. The anharmonicity constant of this vibration is omegax = 6.5 cm-1, giving x = 6.3 x 10(-3). We have also observed asymmetry-induced K doubling for the subbands of A symmetry for K values from 1 to 3 at sufficiently high J values. The size of the splitting coefficients is similar to those observed for the CO-stretch fundamental, with the exception of those for the K = 3A doublet, where the observed splitting is about 18% larger than that for the ground and CO-stretch vCO = 1 states. Copyright 1998 Academic Press.
ABSTRACT
We have studied the infrared spectrum of solid parahydrogen at different orthohydrogen impurity levels in the mid-infrared (MIR) region between 600-2000 cm-1 and in the near infrared/visible (NIR/VIS) region between 10 000-16 500 cm-1. The most important new observations in the MIR region, obtained with a single pass through an absorption cell 4.75 cm in length, are the U0(0) + S0(0) double transition around 1520 cm-1, broadened to about 20 cm-1 by roton delocalization, and the single orthohydrogen transition U0(1) at 1619.12 cm-1, which was previously observed only in normal hydrogen. For the NIR/VIS measurements an internal multireflection cell with 14-cm absorption path length was used. Of particular interest here is the second overtone band of solid hydrogen including double transitions of the type Q2(J) + Q1(J') (J = 0, 1; J' = 0, 1). At 10 241.07 cm-1 the new single transition W2(0) could be observed. For several double transitions in the NIR/VIS region a fine structure is observed, which can be explained by anisotropic interaction in rotationally excited pairs of molecules. The treatment of the fine structure of the Q2(0) + S1(0) transition leads to the prediction of a considerable intensity of the triple transition Q2(0) + Q1(0) + S0(0). Stimulated by this result we have found the triple transitions Q1(0) + Q1(0) + S0(0) at 8660 cm-1 and S1(0) + Q1(0) + S0(0) at 8990 cm-1 in the first overtone region. At 12 788 cm-1 we detected an absorption feature that we have assigned to the triple transition S1(0) + Q1(0) + Q1(0). We explain the infrared activity of this transition in terms of a three-body process, a dipole moment induced within a triplet of hydrogen molecules by successive pairwise induction. Copyright 1998 Academic Press.
ABSTRACT
A reanalysis of the nu3, nu4, and nu6 interacting bands of D2CO has been carried out in the region 850-1250 cm-1 using high-resolution Fourier transform spectra recorded at Giessen. As compared to the previous study of these bands (1987, K. Nakagawa, R. H. Schwendeman, and J. W. C. Johns, J. Mol. Spectrosc. 122, 462-476) higher J and Ka transitions were assigned for the three bands, leading to a better determination of the upper state constants. The v3 = 1, v4 = 1, and v6 = 1 experimental energy levels were introduced in a least-squares fit calculation together with the microwave measurements available in the literature in order to obtain the upper state parameters (band centers, rotational and coupling constants). In this calculation, which allowed us to reproduce both the infrared and the microwave measurements to within their experimental accuracies, the A-, B-, and C-type Coriolis interactions involving the rotational levels belonging to the v4 = 1 and v6 = 1, v3 = 1 and v4 = 1, and v3 = 1 and v6 = 1 interacting states respectively were explicitly taken into account. Finally, from the intensities, a new determination of the relative values of the q3, q4, and q6 first derivatives of the D2CO dipole moment was performed. Copyright 1998 Academic Press. Copyright 1998Academic Press
ABSTRACT
The high resolution Fourier transform far infrared spectrum of the torsion rotation band of CH3OD has been recorded in the range 20-350 cm-1 at a resolution of 0.002 cm-1. The spectrum shows splitting of the lines due to strong torsional, rotational, and vibrational interactions in the molecule. Assignments were possible for rotational subbands in the ground torsional state (n = 0) for K values up to 15 and J values of up to 30, for all the symmetry species. In addition, some subbands were also identified which involve torsionally excited states. A total of 63 b-type subband origins, including 6 Q-branch origins obtained from microwave (MW) and millimeter-wave (MMW) studies, were fitted to a semiempirical model. The molecular parameters so determined were able to reproduce the subband origins almost to within experimental uncertainty. The torsional-rotational state-dependent effective molecular parameters and the asymmetry splitting parameters have also been determined. These should prove valuable in the assignment of transitions involving torsionally excited states in the ground vibrational state. Copyright 1997 Academic Press. Copyright 1997Academic Press
