D. Papoušek

Analysis of high-resolution Fourier transform spectra of 14NH3 at 3.0 μm

Abstract The Fourier transform spectra of ammonia, 14 NH 3 , have been measured in the 2.3-μm region with 0.005-cm −1 resolution. The assignments and the analyses of the ν 1 + ν 2 , ν 2 + ν 3 , and, for the first time, ν 2 + 2 ν 4 bands have been made. Calculations leading to the estimate of the band origin of the ν 2 + 2 ν 4 band have been indicated.

Fourier transform and CARS spectroscopy of the ν1 and ν3 fundamental bands of 14NH3

Abstract The ν 1 and ν 3 fundamental bands of 14 NH 3 have been measured using the techniques of Fourier transform and coherent anti-Stokes Raman spectroscopy. The effective values of the band origins, rotational and centrifugal distortion constants, and parameters of the vibrational-rotational interactions have been obtained by analyzing these bands as essentially regular parallel and perpendicular bands, with the “off-diagonal” local resonance interactions excluded from the fit. The “diagonal” l -type resonance effects have been included into the analysis of the ν 3 band for the + l , K = 1 and − l , K = 2 levels.

Transition dipole matrix elements for 14NH3 from the line intensities of the 2ν2 and ν4 bands

Line intensities as well as self- and nitrogen-broadening coefficients have been determined for 20 transitions in the 2ν2 and ν4 bands of 14NH3 using a diode laser spectrometer. Vibrational-inversional transition moments have been determined for transitions from the ground state to the ν2, 2ν2 and ν4 states by a least-squares fit to the line intensities, taking into account Coriolis and l-type interactions between the nν2 (n = 1, 2, 3), ν4 and ν2 + ν4 states [S. Urban, V. Spirko, D. Papousek, R. S. McDowell, N. G. Nereson, S. P. Belov, L. I. Gershtein, A. V. Maslovskij, A. F. Krupnov, J. Curtis, and K. Narahari Rao, J. Mol. Spectrosc. 79, 455–495 (1980)]. The values of these transition moments have been combined with the previously obtained transition moments for NH3 and its isotopomers to obtain an improved fit to the μz component of the electric dipole moment function of ammonia [cf. V. Spirko, J. Mol. Spectrosc. 74, 456–464 (1979)].

Simultaneous analysis of the microwave and infrared spectra of 14ND3 and 15ND3 for the ν2 excited state

Abstract The data on the inversion spectrum in the ν 2 state of 14 ND 3 [F. Scappini, A. Guarnieri, and G. DiLonardo, J. Mol. Spectrosc. 95 , 20–29 (1982)] have been extended by measuring frequencies of 25 new transitions. A simultaneous least-squares analysis of these data with the ground state microwave transition frequencies and the diode laser measurements of the ν 2 band has been carried out. Improved sets of molecular parameters have been obtained for 14 ND 3 and 15 ND 3 , including the ground and ν 2 state inversion splittings, ν 2 band origins, rotational and centrifugal distortion constants, and the parameters of the Δ k = ±3 n vibrational-rotational interactions.

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

Abstract More than 800 Δ k = ±2 and 60 Δ k = ±3 forbidden transitions to the ν 4 and 2 ν 2 vibrational levels, respectively, have been assigned in the Fourier transform spectra of 15 NH 3 , 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 ν 2 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.

Third-order theory of the line intensities in the allowed and forbidden vibrational−rotational bands of C3v molecules

Abstract A third-order theory of the intensities of the allowed and “forbidden” (perturbation-allowed) transitions to the fundamental vibrational levels of C 3 v semirigid molecules has been worked out by using the method of contact transformations applied to the electric dipole moment operator. Explicit expressions have been obtained for the linestrengths of the allowed (Δ k = 0, ±1) as well as forbidden (Δ k = ±2, ±3, ±4) transitions from the ground vibronic state to the fundamental vibrational levels of C 3 v molecules. The treatment takes into account all the important Coriolis and anharmonic interactions in a C 3 v molecule, including the effect of the “2, 2” and “2, −1” l -type interactions and the Δ k = ±3 interactions on the intensities of the allowed and forbidden vibrational-rotational transitions. The expressions for the linestrengths of the allowed and forbidden transitions are given here in a form suitable to fit the experimental data on the intensities in the vibrational-rotational spectra of C 3 v molecules.

Simultaneous Rovibrational Analysis of the ν2, ν3, ν5, and ν6 Bands of H312CF

Abstract A total of 4892 transition wavenumbers of the ν 2 , ν 3 , ν 5 , and ν 6 fundamental bands of H 3 12 CF and 1469 frequencies of the rotational transitions in the v 2 = 1, v 3 = 1, v 5 = 1, and v 6 = 1 vibrational states have been fitted simultaneously by taking explicitly into account various Coriolis interactions, l -type interactions, and α-resonance terms between and within the vibrational states. The standard deviation of the fit using 71 parameters was 8.10 × 10 −5 cm −1 for the infrared data and 0.198 MHz for the rotational data. This study clearly shows that in order to obtain a really quantitative fit of the highly precise data of vibration–rotational and rotational spectroscopy, it is necessary to fit all the data simultaneously using a variational approach. The deperturbed values of the upper state rotational constants differ significantly from those obtained previously in fitting the ν 3 and ν 6 bands as isolated bands and the ν 2 /ν 5 bands by a variational approach. This is important for the precise determination of the equilibrium structure of methyl fluoride (J. Demaison, J. Breidung, W. Thiel, and D. Papousek, Struct. Chem., in press). Besides this, the results can be used in further studies of the reduced Hamiltonians for more complicated systems of interacting vibrational levels.

High-resolution Fourier transform and submillimeter-wave study of the ν6 band of 12CH3F

Abstract The ν 6 band of 12 CH 3 F has been measured in the range 1077–1278 cm −1 using a Fourier transform spectrometer with a resolution of 0.002 cm −1 . The wavenumbers of 1070 rovibrational transitions have been used simultaneously with 99 previously reported frequencies of the ground state rotational transitions and 135 frequencies of rotational transitions in the v 6 = 1 excited vibrational state to determine 24 parameters of the ν 6 band and 6 spectroscopic parameters of the ground vibrational state of 12 CH 3 F.

Effective Hamiltonian for degenerate vibrational states in symmetric top molecules

Abstract A mixed matrix-operator form of the effective rotational Hamiltonian has been discussed for the degenerate vibrational states of symmetric top molecules. In this scheme, a rotational contact transformation can be applied to the effective Hamiltonian such that the operators of the “2, +2,” “2, −2,” and “2, −1” l -type interactions as well as the operators of the Δ k = ±3 and ±4 interactions are eliminated from the first-order terms of the expansion of the rotational Hamiltonian in terms of the small parameter λ. The results have been used to discuss the correlation between various interaction parameters in the effective rotational Hamiltonian for the doubly degenerate fundamental vibrational levels of semirigid symmetric top molecules. For example, for C 3 v or D 3 molecules, the parameter of the “2, −1” interaction is correlated with other parameters and cannot be determined separately by fitting the experimental data (unless there are certain accidental resonances between vibrational-rotational levels).

Submillimeter-wave spectra of 12CH3F in the v2 = 1 and v5 = 1 vibrational states

Abstract Transition frequencies of the pure rotational transitions in the v 2 = 1 and v 5 = 1 vibrational states of 12 CH 3 F between 180 and 610 GHz have been measured using the submillimeter-wave spectrometer with acoustic detection RAD3. Twenty-two spectroscopic parameters describing the vibration-rotation interactions within and between the v 2 = 1 and v 5 = 1 states have been fitted using a reduced effective Hamiltonian for interacting vibrational states proposed by Lobodenko et al. [J. Mol. Spectrosc. 126 , 159–170 (1987)].