Franck–Condon Factors for the Ã←X̃ Transition of Ammonia with Anharmonic Potential Functions for the Ground and Excited States

Abstract

The Franck–Condon factors for the Ã←X̃ transition in NH3 have been calculated and compared with the observed relative intensities of electron impact spectra. Calculations were made in which the symmetric bending mode was fitted as an anharmonic oscillator. In addition, the Franck–Condon factors were calculated for the case in which all vibrations were approximated as harmonic. The former calculations best fit the observed intensity distribution. The Ã←X̃ transition consists of overlapping bands in which the symmetric stretching and bending vibrations of the à state are excited. The symmetric stretching frequency of the ã state is estimated to be 2900 ± 50 cm−1.

Microwave detected, microwave-optical double resonance of NH3, NH2D, NHD2, and ND3. I. Structure and force field of the à state

“…They proposed that this discrepancy was due to errors caused by neglect of vibration-rotation interactions in reducing the observed rotational constants to an equilibrium geometry. The smaller displacement in this coordinate reduces the expected intensity of the missing ν 1 progression compared to the previous estimates [7].…”

“…Anomalous centrifugal distortion constants were obtained for both the ND 3 2 0 and 2 1 levels indicating significant interaction with a nearby level. (5) 46125.220 0.147 R 4 (5) 46238.290 1.782 Q 5 (5) 46114.120 0.052 R 5 (5) 46228.680 0.495 Q 6 (6) 46098.280 0.049 R 6 (6) 46230.880 0.797 P 6 (7) 45958.160 0.842 Q 6 (7) 46095.960 0.078 R 6 (7) 46251.720 0.590 Q 7 (7) 46079.610 0.076 R 7 (7) 46234.240 0.545 Q 8 (8) 46058.270 0.060 R 8 (8) 46233.910 1.113 Q 9 (9) 46034.510 0.224 2 1 band. (7) 48671.300 0.730 Q 6 (7) 48775.800 0.130 R 6 (7) 48912.700 0.600 Q 7 (7) 48788.000 0.140 (17) Numbers in parentheses are ±1σ.…”

A full-dimensional coupled-surface study of the photodissociation dynamics of ammonia using the multiconfiguration time-dependent Hartree method

“…The photodissociation dynamics of ammonia have been studied extensively both experimentally 1-32 and theoretically [33][34][35][36][37][38][39][40][41][42][43][44][45] over the past few decades, as it constitutes a prototype system for non-planar to planar electronic transition, vibrational predissociation and nonadiabatic dynamics. For such a seemingly simple molecule, the complexity of behaviour is arising from a combination of its textbook example of umbrella motion and the conical intersection for the ground and first electronically excited singlet states.…”

“…However, there is no experimental evidence for this excitation. Two principal hypotheses [33][34][35] have been proposed to explain the non-appearance of ν 1 : (a) the near 3:1 degeneracy of the ν 1 and ν 2 modes and hence the dominating ν 2 bands masks the weak separate ν 1 progression; (b) that the excitation of the ν 1 mode causes rapid predissociation or dissociation, resulting in an essentially continuum absorption rather than a discrete band.…”

Franck–Condon factors in curvilinear coordinates: the photoelectron spectrum of ammonia

“…The intensities of the higher-energy transitions are significantly underestimated, and therefore, the spectrum exhibits only 13 peaks, whereas in the experimental one at least 16 peaks are clearly observed. The results obtained by using a harmonic potential are thus in many aspects similar to those previously obtained by employing the internal coordinate representation but using a simplified expression ofT; without including the DT terms [10,44]. Indeed, the DT kinetic operator only provides corrections of a few tens of cm -1 on the computed energies, without significantly affecting the computed eigenvectors.…”