Internally contracted multiconfiguration-reference configuration interaction calculations for excited states

1992 ◽  
Vol 84 (1-2) ◽  
pp. 95-103 ◽  
Author(s):  
Peter J. Knowles ◽  
Hans-Joachim Werner
Keyword(s):  
Excited States ◽  
Configuration Interaction ◽  
Reference Configuration ◽  
Configuration Interaction Calculations

Ab initio MRD-CI Study of the Electronic Spectrum of Tribromomethanol Br3COH and the Photofragmentation along Br–C and C–O Cleavage

2003 ◽  
Vol 217 (3) ◽  
pp. 241-254
Author(s):  
M. Mühlhäuser
Keyword(s):  
Energy Range ◽  
Ab Initio ◽  
Electronic Spectrum ◽  
Oscillator Strength ◽  
Excited States ◽  
Atmospheric Chemistry ◽  
Configuration Interaction ◽  
Reference Configuration ◽  
Triplet States ◽  
Configuration Interaction Calculations

AbstractMulti reference configuration interaction calculations are carried out to compute the electronic spectrum of tribromomethanol Br3COH. The first dipole-allowed transitions are computed at 5.0 eV (11A″ ← X1A′) and 5.4 eV (21A″ ← X1A′) followed by three transitions at 5.5 eV (21A′ ← X1A′) and 6.1 eV (31A′ ← X1A′, 31A″ ← X1A′). The largest oscillator strength (f = 0.08) is obtained for the σ → σ* type excitation 31A″ ← X1A′ computed around 6.1 eV. The corresponding triplet states are also given. Five low-lying excited states in the energy range between 4.5 eV and 5.5 eV are found to be highly repulsive for Br–C elongation, leading to Br2CHOH (X2A′) and Br (X2P), so that tribromomethanol Br3COH is expected to be important for atmospheric chemistry as reservoir of Br radicals. Photodissociation along C–O cleavage resulting in Br3C (X2A′) and OH (X2Π) has to overcome a barrier of about 0.7 eV because the low-lying excited states 11A″, 13A′ and 13A″ become repulsive only after elongating the C–O bond by about 0.45 Å.

The Importance of Photodissociative Trichloromethanol for Atmospheric Chemistry

2003 ◽  
Vol 68 (12) ◽  
pp. 2297-2308 ◽  
Author(s):  
Max Mühlhäuser ◽  
Melanie Schnell ◽  
Sigrid D. Peyerimhoff
Keyword(s):  
Energy Range ◽  
Excited States ◽  
Atmospheric Chemistry ◽  
Configuration Interaction ◽  
Configuration Interaction Calculations

Multireference configuration interaction calculations are carried out for ground and excited states of trichloromethanol to investigate two important photofragmentation processes relevant to atmospheric chemistry. For CCl3OH five low-lying excited states in the energy range between 6.1 and 7.1 eV are found to be highly repulsive for C-Cl elongation leading to Cl2COH (X2A') and Cl (X2P). Photodissociation along C-O cleavage resulting in Cl3C (X2A') and OH (X2Π) has to overcome a barrier of about 0.8 eV (13A'', 11A'') and 1.2 eV (13A') because the low-lying excited states 11A'', 13A' and 13A'' become repulsive only after elongating the C-O bond by about 0.3 Å.

Modification of HAM/3 excitation energies for ΠΠ* transitions of linear molecules

1980 ◽  
Vol 58 (16) ◽  
pp. 1687-1690 ◽  
Author(s):  
Delano P. Chong
Keyword(s):  
Excitation Energy ◽  
Explicit Expression ◽  
Excited States ◽  
Configuration Interaction ◽  
Excitation Energies ◽  
Carbon Suboxide ◽  
Numerical Examples ◽  
Energy Correction ◽  
Linear Molecules ◽  
Configuration Interaction Calculations

The excitation energies calculated by the HAM/3 procedure for ΠΠ* transitions in linear molecules can be internally inconsistent by as much as ± 0.6 eV. In the recent study by Åsbrink etal., the problem was avoided by adopting Recknagel's expressions and requiring the proper average ΠΠ* excitation energy. In this paper, we trace the small inconsistency back to its origin in HAM/3 theory and derive the analytical expression for the energy correction as well as Recknagel's formulas. Numerical examples studied include all seven linear molecules investigated by Åsbrink etal. The explicit expression for the correction enables us to perform meaningful configuration-interaction calculations on the excited states, as illustrated by the carbon suboxide molecule.

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