ANOMALOUS ROTATIONAL LINE INTENSITIES IN ELECTRONIC TRANSITIONS OF POLYATOMIC MOLECULES: AXIS-SWITCHING

1965 ◽  
Vol 43 (2) ◽  
pp. 298-320 ◽  
Author(s):  
J. T. Hougen ◽  
J. K. G. Watson
Keyword(s):  
Electronic State ◽  
Electronic Transition ◽  
Electronic States ◽  
Polyatomic Molecules ◽  
Electronic Transitions ◽  
Rotational Line ◽  
Line Intensities ◽  
Fixed Axis ◽  
Axis Switching ◽  
Equilibrium Geometries

It is convenient when performing calculations on a vibrating and rotating molecule to define an axis system which is somehow fixed to the molecule. The orientation of the usual molecule-fixed axis system, however, depends not only upon the instantaneous positions of the nuclei, but also upon the equilibrium positions from which the nuclei are regarded as being displaced. Thus, when a molecule of low enough symmetry undergoes an electronic transition accompanied by a change in geometry, it will, in general, be necessary to consider two molecule-fixed axis systems, corresponding to the two different electronic states. This change in axis system from one electronic state to another will be called axis-switching. The two axis systems can be related to each other by the 3 × 3 rotation matrix which brings them into coincidence. The elements of this matrix are functions of the equilibrium geometries of the two electronic states as well as of the instantaneous positions of the atoms in the molecule. Axis-switching leads to departures from the usual expressions for the intensities of rotational lines, the effects of which are most noticeable in near-symmetric tops. The forbidden subbands occurring in the 2 400 Å system of acetylene can be satisfactorily explained by axis-switching. Axis-switching effects may also be present in the spectra of HCN, HSiCl, and HSiBr.

Theoretical search for the Rydberg dimer of H3

1994 ◽  
Vol 72 (11-12) ◽  
pp. 866-870
Author(s):  
James S. Wright
Keyword(s):  
Potential Energy ◽  
Electronic State ◽  
Rydberg State ◽  
Electronic States ◽  
Electronic Transitions ◽  
Energy Minimum ◽  
Outer Electron ◽  
Small Distortion ◽  
Potential Energy Minimum

The lowest lying bound electronic state of H3 has the equilateral triangular H3+ core, with an outer electron in the 2s Rydberg orbital. Electronic transitions to this [Formula: see text] state were first observed by Herzberg and co-workers. Combining two such Rydberg monomers into a spin-paired Rydberg dimer may lead to significant stabilization at a long geometry where the 2s orbitals overlap. This paper includes the search for such an electronic state, as well as discussion of other electronic states that are unbound. Although the dimer state is not the lowest lying electronic state, it does show a substantial potential energy minimum at a ring–ring distance of 6.75 bohr. The D3h symmetry for the Rydberg state is broken by a small distortion that leads to an isoceles triangle.

scholarly journals Stability of polyatomic molecules in degenerate electronic states - I—Orbital degeneracy

1937 ◽  
Vol 161 (905) ◽  
pp. 220-235 ◽  
Keyword(s):  
Electronic State ◽  
Stable Equilibrium ◽  
Equilibrium Configuration ◽  
Great Influence ◽  
Electronic States ◽  
Electronic Energy ◽  
Polyatomic Molecules ◽  
Orbital Degeneracy ◽  
Straight Line ◽  
Accidental Degeneracy

In the following we investigate the conditions under which a polyatomic molecule can have a stable equilibrium configuration when its electronic state has orbital degeneracy, i. e. degeneracy not arising from the spin. We shall show that stability and degeneracy are not possible simultaneously unless the molecule is a linear one, i. e. unless all the nuclei in the equilibrium configuration lie on a straight line. We shall see also that the instability is only slight if the degeneracy is due solely to electrons having no great influence on the binding of the molecule. We first note that if accidental degeneracy (i. e. degeneracy not caused by symmetry) is disregarded then a degenerate electronic state necessarily entails a symmetrical nuclear configuration. Thus in order to cover all cases we may first consider each possible type of symmetry separately and discuss what nuclear configurations are consistent with each symmetry. A given molecule will possess a continuous set of configurations consistent with one definite type of symmetry, and among these configurations there may be one with a minimum electronic energy. This configuration is then stable with respect to all totally symmetrical nuclear displacements (i. e. displacements which do not disturb the symmetry). We shall have to investigate its stability with respect to all other nuclear displacements.

Rotational line intensities in 3Σ–1Σ electronic transitions

1968 ◽  
Vol 46 (14) ◽  
pp. 1637-1643 ◽  
Author(s):  
James K. G. Watson
Keyword(s):  
Electronic Transitions ◽  
Spin Interaction ◽  
Rotational Line ◽  
Line Intensities ◽  
Transition Moments ◽  
Linear Molecules

Formulae are given for the intensities of rotational lines in 3Σ–1Σ electronic transitions of linear molecules, allowing for the effects of spin–spin interaction. For [Formula: see text] transitions an error in the relative phases of the two transition moments in the work of Schlapp (1932) is corrected. Recent observations on SO and HCP support this change in phases.

On the Electronic States of S4+ and S4- Isomers

2007 ◽  
Vol 72 (1) ◽  
pp. 83-99 ◽  
Author(s):  
Hanka Sormova ◽  
Roberto Linguerri ◽  
Pavel Rosmus ◽  
Jürgen Fabian ◽  
Najia Komiha
Keyword(s):  
Electronic Transition ◽  
Electronic States ◽  
Theoretical Data ◽  
Electron Affinities ◽  
Excitation Energies ◽  
Ionization Energies ◽  
Transition Moments ◽  
Higher Spin ◽  
Large Amplitude Vibrations ◽  
Equilibrium Geometries

For three energetically most stable structures of tetrasulfur, S4, S4+ and S4- (cis-chain, rectangular, and trans-chain forms), equilibrium geometries, harmonic wavenumbers, ionization energies, electron affinities, electronic vertical and adiabatic excitation energies, and electronic transition moments were calculated by ab initio methods. It was found that similarly to the ground state of S4, the S4+ cis-isomer could interconvert, perturbed, however, by vibronic coupling with a very close-lying excited state and large-amplitude vibrations. Moreover, the cis- and rectangular minima are calculated to be energetically degenerated. The ω values in all three species agree reasonably well with existing experimental and theoretical data. The calculated patterns of harmonic modes suggest the existence of very complex low-lying anharmonic polyads in all three species. The calculated ionization energies reported previously are compared with the present more accurate data. Also the electronic transition moments and the energy positions of the electronic states with higher spin multiplicities are given.

AsCl radical: The low-lying electronic states and the (1) 3 Π → X 3 Σ − electronic transition

2015 ◽  
Vol 634 ◽  
pp. 66-70 ◽  
Author(s):  
Marcelo A.P. Pontes ◽  
Marcos H. de Oliveira ◽  
Luiz F.A. Ferrão ◽  
Orlando Roberto-Neto ◽  
Joaquim D. Da Motta Neto ◽  
...  
Keyword(s):  
Electronic Transition ◽  
Electronic States
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