High resolution 0.004 and 0.01 cm-1 instrumental bandwidth interferometric Fourier transform infrared spectra of 14NH2D and 14ND2H were measured on a Bomem DA002 spectrometer in a supersonic jet expansion and at room temperature. We report the analysis of the bending fundamentals of 14NH2D with term values Tvs=1389.90632 cm-1 and Tva =1390.49532 cm-1 for the 4b fundamental and Tvs=1605.64047 cm-1 and Tva =1591.00197 cm-1 for the 4a fundamental, and of 14ND2H with term values of Tvs =1233.37402 cm-1 and Tva=1235.89042 cm-1 for the 4a fundamental and Tvs =1461.79419 cm-1 and Tva=1461.991819 cm-1 for the 4b fundamental. In all cases Tvs gives the position of the symmetric inversion sublevel with positive parity and Tva the position of the antisymmetric inversion sublevel with negative parity. The notation for the fundamentals 4a and 4b is chosen by correlation with the degenerate 4 mode in the C3v symmetric molecules NH3 and ND3. The degeneracy is lifted in Cs symmetry and a indicates the symmetric, b the antisymmetric normal mode with respect to the Cs symmetry plane in NH2D and ND2H. Assignments were established with certainty by means of ground state combination differences. About 20 molecular parameters of the effective S-reduced Hamiltonian could be determined accurately for each fundamental. In particular, the effect of Fermi resonances of the 22 overtone with the 4a bending mode was observed, leading to an increased inversion splitting in the case of ND2H and to a strongly increased inversion splitting and an inverted order of the two inversion levels in NH2D. Rotational perturbations observed with the 4b bending fundamentals are probably due to Coriolis interactions with the inversion overtone 22. The results are important for understanding isotope effects on the inversion in ammonia as well as its selective catalysis and inhibition by excitation of different vibrational modes, as treated by quantum dynamics on high dimensional potential hypersurfaces of this molecule. © 2006 American Institute of Physics.
Mode selective tunnelling dynamics observed by high resolution spectroscopy of the bending fundamentals of 14ND2H and 14NH2D
Snels M;
2006
Abstract
High resolution 0.004 and 0.01 cm-1 instrumental bandwidth interferometric Fourier transform infrared spectra of 14NH2D and 14ND2H were measured on a Bomem DA002 spectrometer in a supersonic jet expansion and at room temperature. We report the analysis of the bending fundamentals of 14NH2D with term values Tvs=1389.90632 cm-1 and Tva =1390.49532 cm-1 for the 4b fundamental and Tvs=1605.64047 cm-1 and Tva =1591.00197 cm-1 for the 4a fundamental, and of 14ND2H with term values of Tvs =1233.37402 cm-1 and Tva=1235.89042 cm-1 for the 4a fundamental and Tvs =1461.79419 cm-1 and Tva=1461.991819 cm-1 for the 4b fundamental. In all cases Tvs gives the position of the symmetric inversion sublevel with positive parity and Tva the position of the antisymmetric inversion sublevel with negative parity. The notation for the fundamentals 4a and 4b is chosen by correlation with the degenerate 4 mode in the C3v symmetric molecules NH3 and ND3. The degeneracy is lifted in Cs symmetry and a indicates the symmetric, b the antisymmetric normal mode with respect to the Cs symmetry plane in NH2D and ND2H. Assignments were established with certainty by means of ground state combination differences. About 20 molecular parameters of the effective S-reduced Hamiltonian could be determined accurately for each fundamental. In particular, the effect of Fermi resonances of the 22 overtone with the 4a bending mode was observed, leading to an increased inversion splitting in the case of ND2H and to a strongly increased inversion splitting and an inverted order of the two inversion levels in NH2D. Rotational perturbations observed with the 4b bending fundamentals are probably due to Coriolis interactions with the inversion overtone 22. The results are important for understanding isotope effects on the inversion in ammonia as well as its selective catalysis and inhibition by excitation of different vibrational modes, as treated by quantum dynamics on high dimensional potential hypersurfaces of this molecule. © 2006 American Institute of Physics.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
