Š. Urban

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.

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.

Effective rotational Hamiltonians of pyramidal XY3 molecules with the inversion splittings of energy levels

A procedure using the contact transformation method is developed to derive effective rotational Hamiltonians of ammonia-like molecules from a nonrigid molecular Hamiltonian. The reducibility of these effective Hamiltonians is examined in relation to their dependence on the magnitude of inversion splittings. Expressions for energy levels appropriate for analyses of experimental data are derived for nondegenerate vibrational states as well as for degenerate vibrational states with one quantum of an E vibration excited.

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).

Intensities in the ν4 band of 15NH3

Abstract Line intensities and nitrogen-broadening coefficients of 33 transitions in the ν 4 band of 15 NH 3 have been measured using a diode laser spectrometer. The interpretation of the strongly perturbed line intensities was based on the third-order theory of linestrengths of axially symmetric XY 3 molecules. The analysis yields effective transition moments and the vibrational band strengths of the ν 4 band. It was also possible to determine parameters of the “2, 2” l -type interaction in the ν 4 state.

Interpretation of intensities of forbidden vibration-rotation transitions in Fourier transform spectra of ammonia

Abstract The absolute intensities of forbidden Δk = ±2 transitions to the ν4 vibrational state of 14NH3 have been derived from the Fourier transform spectra measured with the multipass White-type cell. Using expressions derived by the contact transformation method, the intensity data have been analyzed in order to obtain information on the mixing of vibration-rotation wavefunctions with different values of quantum numbers (k − lt). The parameter γ4 of the “2, −1” l-type operator, which is indeterminable from an anlaysis of transition frequencies because of correlations in the reduced Hamiltonian, has been determined to be 0.0563 (16) cm−1.

Contact transformations leading to effective rotational Hamiltonians for degenerate vibrational states of symmetric top molecules

Abstract Contact transformations are described in this paper for symmetric top molecules which remove the “2, +2” and “2, −1” l -type operators as well as the operators of the Δ k = ±3 interactions from the first-order terms of the expansion of the vibrational-rotational Hamiltonian in terms of the smallness parameter λ. The results are presented in a form which makes it possible to obtain effective rotational Hamiltonians for a general vibrational state Π s | v s 〉 Π t | v t l t 〉, where v s and v t are the vibrational quantum numbers pertaining to the nondegenerate and degenerate vibrational modes, respectively. A detailed discussion is given of the effective rotational Hamiltonian for the vibrational states | v t l t = 2 ±2 , 2 0 〉 of molecules of C 3 v or D 3 symmetry.

Contact transformations in the mixed matrix-operator form: Effective rotational Hamiltonians for the excited vibrational states of symmetric top molecules

The effective rotational Hamiltonian for C3v or D3 molecules written in the basis of the vibrational wavefunctions |2±2> and |20> has been transformed by a rotational contact transformation such that the operators of thel-type interactions and of the Δl=0, Δ k≠0 interactions are eliminated from the first order terms of the expansion of the Hamiltonian in terms of the smallness parameter λ.