Vibrational energy levels for symmetric and asymmetric isotopomers of ammonia with an exact kinetic energy operator and new potential energy surfaces

Abstract

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Treatment of nonlinear optical properties due to large amplitude anharmonic vibrational motions: Umbrella motion in NH3

“…The mean absolute deviation ͑MAD͒ and maximum absolute deviation ͑MAXAD͒ obtained for the energy levels with MP2 / POL/ turns out to be better than the 1D CCSD͑T͒/aug-cc-pvTZ values obtained by Pesonen et al 55 Although the deviations are significantly larger for the MP2 / POL/ z energy levels, which are more important than inversion splittings for vibrational ͑hyper͒polarizabilities, we obtain the MP2/POL properties for z as well as in order to see how sensitive the results are to the choice of coordinate. Of course, the MAD can be reduced by increasing the dimensionality to two dimensional 55 and six dimensional [56][57][58] Indeed, our third goal is to see the effect of reducing the dimensionality.…”

Complex symmetrized calculations on ammonia vibrational levels

“…The quantum mechanical treatment is greatly reduced if the eigenfunctions of H when real symmetrized vibrational coordinates are used [20][21][22][23]. To derive complex symmetry adapted orthogonal N-H stretch wavefunctions ϕ corresponding to a configuration p 1 k 2 l 3 , simple linear combinations must be taken, by rotating the original configura-…”

“…For this reason, extensive spectroscopic measurements have been performed on 14 NH 3 as well as on its isotopomers [1][2][3][4][5][6], in a wide spectral range. Many theoretical studies have also been carried out to rationalize the extremely complicated NH 3 PES and ro-vibrational spectrum [2,3,[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. Ammonia is a symmetric top molecule, belonging to the point group D 3h [1,7,27].…”

Reproducing Deep Tunneling Splittings, Resonances, and Quantum Frequencies in Vibrational Spectra From a Handful of Direct Ab Initio Semiclassical Trajectories

“…The deuterated ammonia spectrum resulted also to be in very good agreement with one on an accurate PES. 29 Another simulation consists in evaluat- ing the effect of the change in the value ofh on tunneling splittings calculated using the MLT PES.…”

“…For this reason, on the upper panel of Figure Figure 3, peaks are slightly more spaced than in Figure Figure 2 , however all vibrational features observed in Figure Figure 2 are preserved in Figure Figure 3. To prove the quantum mechanical nature of the splittings and vibrational couplings (including the Darling-Dennison resonance 29 between the nearly equal stretching 27 . f The vibrational terms.…”