Ultraviolet spectra of non-alternant hydrocarbons: The significance of non-neighbour resonance integrals and of configuration-interaction

1968 ◽  
Vol 21 (8) ◽  
pp. 1939 ◽  
Author(s):  
RD Brown ◽  
FR Burden ◽  
GR Williams
Keyword(s):  
Molecular Orbital ◽  
Excited States ◽  
Configuration Interaction ◽  
Molecular Orbital Calculation ◽  
Alternative Methods ◽  
General Level ◽  
Nearest Neighbours ◽  
Alternant Hydrocarbon ◽  
Alternant Hydrocarbons ◽  
Method Of Evaluation

A study has been made of the way in which the calculated positions of excited states of non-alternant hydrocarbons are affected by (a) including all resonance integrals rather than just those for nearest neighbours (b) including configuration-interaction. The VESCF molecular-orbital technique, with two alternative methods for deriving basic integrals, was employed. Predicted positions of excited states are found to be sometimes appreciably altered when all resonance integrals are included, and are somewhat dependent upon the method of evaluation of basic integrals. We conclude that one should be cautious in interpreting U.V. spectra from an isolated molecular-orbital calculation on a non-alternant hydrocarbon. The study of the effect of configuration-interaction for the excited states of fulvene and dimethylenecyclobutene yields results analogous to those found by Koutecky and co-workers for benzene. The predicted relative positions of some excited states are altered when doubly excited configurations are included, but the general level of energies predicted for lower excited states when only singly excited configurations are used is probably close to the result that would be found when up to triply excited configurations are included.

Molecular orbital calculations on dinitrogen trioxide, N2O3

1977 ◽  
Vol 30 (12) ◽  
pp. 2613 ◽  
Author(s):  
IJ Doonan ◽  
RGAR Maclagan
Keyword(s):  
Molecular Orbital ◽  
Excited States ◽  
Molecular Orbital Calculation ◽  
Molecular Orbitals ◽  
Basis Set ◽  
Molecular Orbital Calculations ◽  
Localized Molecular Orbitals ◽  
Expansion Technique ◽  
Doubly Excited ◽  
Slater Basis

A minimal Slater basis set molecular orbital calculation on dinitrogen trioxide, N2O3, is reported. In the evaluation of integrals, non-NDDO integrals were calculated by the 3G/s expansion technique. Analysis of the wave function obtained shows weak bonding between the nitrosyl and nitro fragments and a very weak attractive interaction between the cis- oxygens. The molecular orbitals for N2O3 were expanded in terms of the NO and NO2 molecular orbitals. A correlation diagram linking the N2O3 orbitals with the NO and NO2 orbitals is presented. The localized molecular orbitals for N2O3 are analysed. A configuration interaction calculation involving the ground state and nine doubly excited state configurations is reported. Two excited states have significant contributions. A comparison is made between the results obtained by using a 3G/S expansion and a calculation using a 2G/S expansion.

Haloalkane-Aromatic Complexes in the Ground and Excited States Molecular Orbital Calculation

1980 ◽  
Vol 35 (4) ◽  
pp. 418-422 ◽  
Author(s):  
I. M. Brinn
Keyword(s):  
Molecular Orbital ◽  
Excited States ◽  
Ground State ◽  
Substituent Effect ◽  
Molecular Orbital Calculation ◽  
Complex Stability ◽  
Excited Singlet ◽  
Singlet States ◽  
Aromatic Complexes ◽  
Excited Singlet States

Abstract CNDO/2 calculations have been carried out on a series of haloalkane-aromatic 1: 1 complexes in the ground and first excited singlet states and one 2 : 1 complex in the ground state. Calculated stabilities agree very well with reported experimental results for the ground state. Our calculations indicate that the substituent effect on complex stability in excited states will be the opposite of that found for the ground state.

Parallel Fock Matrix Construction Algorithm for Molecular Orbital Calculation Specific Computer

2006 ◽  
Vol 5 (1) ◽  
pp. 179-188
Author(s):  
Hiroaki UMEDA ◽  
Yuichi INADOMI ◽  
Hiroaki HONDA ◽  
Umpei NAGASHIMA
Keyword(s):  
Molecular Orbital ◽  
Molecular Orbital Calculation ◽  
Construction Algorithm ◽  
Matrix Construction

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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