SEMIEMPIRICAL SCF CALCULATIONS ON AZULENE AND ITS SINGLY CHARGED IONS

1965 ◽  
Vol 43 (11) ◽  
pp. 3026-3038 ◽  
Author(s):  
J. E. Bloor
Keyword(s):  
Dipole Moment ◽  
Excited States ◽  
Ground State ◽  
Basis Set ◽  
Bond Orders ◽  
Electron Charge Density ◽  
Charge Densities ◽  
Bond Lengths ◽  
Set Agreement ◽  
Singly Charged

SCF MOs for azulene have been obtained by the semiempirical Pariser, Parr, Pople procedure using the Nishimoto–Mataga method of calculating repulsion integrals and the assumption that nearest neighbor resonance integrals are independent of interatomic distance. Excited states calculated from these MOs by a CI calculation are in very good agreement with experiment. Ground state charge densities, bond orders, and the dipole moment are similar to other SCFMO calculations and reveal no disadvantage in adopting a constant resonance integral for all bonds. It is shown that estimates of the π-electron charge density by n.m.r. methods are not compatible with direct dipole moment measurements and it is suggested that the interpretation of the n.m.r. measurements suffers from inaccuracies in estimating ring currents. Doubt is also thrown on the use of simple relationships between calculated π-bond orders and bond lengths obtained by X-ray crystallographic measurements on the solid state, particularly since all the bond lengths in azulene are predicted to be longer than in benzene whereas experiment shows some to be shorter. Calculations on spin densities and charge densities of the singly charged azulene anion and cation have been performed by a restricted Hartree–Fock perturbation method in which the matrix elements for the interaction between singly excited states and the ground state are calculated using the closed shell SCFMOs of azulene as the basis set. Agreement with experiment for the anion is fairly good. For the cation our results are in severe disagreement with recent VB calculations, but there are no experimental results available to decide between the two methods.

Bond order-bond length relationships in conjugated hydrocarbons - the microwave spectrum and structure of 3,4-dimethylenecyclobutene

1983 ◽  
Vol 36 (4) ◽  
pp. 639 ◽  
Author(s):  
RD Brown ◽  
PD Godfry ◽  
BT Hart ◽  
AL Ottrey ◽  
M Onda ◽  
...  
Keyword(s):  
Dipole Moment ◽  
Ab Initio ◽  
Bond Length ◽  
Bond Order ◽  
Microwave Spectrum ◽  
Basis Set ◽  
Molecular Orbital Calculations ◽  
Bond Orders ◽  
Bond Lengths ◽  
Typical Error

The microwave spectrum of the benzene isomer 3,4-dimethylenecyclobutene including spectra of all possible single 13C-substituted and sufficient singly and doubly D-substituted species to give a complete r5 geometry, have been measured and analysed. An estimate of the re geometry has also been derived. The additional precise CC bond lengths obtained for an unsubstituted, conjugated hydrocarbon enable us to examine bond order-bond length relationships more thoroughly than has previously been possible. The CC bond lengths exhibit a noticeably better correlation with SCFMO bond orders than with simple H�ckel bond orders. Further confirmatory measurements of the dipole moment of dimethylenecyclobutene have been made. Ab initio molecular orbital calculations using a 6-31G basis set give an optimized geometry with CC bond lengths within 2 pm of the r5 values. The computed dipole moment agrees almost exactly with experiment but a corresponding calculation on fulvene is discrepant with experiment by 0.16 D, which is probably a more typical error.

scholarly journals The Microwave Spectrum of 3,4-Dihydro-1,2-Pyran

1985 ◽  
Vol 40 (9) ◽  
pp. 913-919
Author(s):  
Juan Carlos López ◽  
José L. Alonso
Keyword(s):  
Dipole Moment ◽  
Excited States ◽  
Ground State ◽  
Principal Axis ◽  
Microwave Spectrum ◽  
Average Intensity ◽  
Ring Conformation ◽  
Vibrationally Excited ◽  
Rotational Constants ◽  
Displacement Measurements

Abstract The rotational transitions of 3,4-dihydro-1,2-pyran in the ground state and six vibrationally excited states have been assigned. The rotational constants for the ground state (A = 5198.1847(24), B = 4747.8716(24) and C = 2710.9161(24) have been derived by fitting μa, μb and μc-type transitions. The dipole moment was determined from Stark displacement measurements to be 1.400(8) D with its principal axis components |μa| =1.240(2), |μb| = 0.588(10) and |μc| = 0.278(8) D. A model calculation to reproduce the ground state rotational constants indicates that the data are consistent with a twisted ring conformation. The average intensity ratio gives vibrational separations between the ground and excited states of the ring-bending and ring-twisting modes of ~ 178 and ~ 277 cm-1 respectively.

The ground state and low-lying excited states of CCCN radical and its ions: a CASSCF/CASPT2 study

2016 ◽  
Vol 94 (9) ◽  
pp. 803-807
Author(s):  
Angyang Yu
Keyword(s):  
Excited States ◽  
Ground State ◽  
Linear Structure ◽  
Electronic Configuration ◽  
Geometric Optimization ◽  
Oscillator Strengths ◽  
Basis Set ◽  
Excitation Energies ◽  
Complete Active Space ◽  
Vertical Excitation

The ground state and low-lying excited states of the CCCN radical and its ions have been investigated systematically using the complete active space self-consistent field (CASSCF) and multi-configuration second-order perturbation theory (CASPT2) methods in conjunction with the ANO-RCC-TZP basis set. The calculated results show that the state 12Σ+ has the lowest CASPT2 energy among the electronic states. By means of the geometric optimization of this radical, it could be found that the molecule exhibits linear structure, with the bond lengths R1 = 1.214 Å, R2 = 1.363 Å, R3 = 1.162 Å, which are very close to the experimental values. The calculated vertical excitation energies and the corresponding oscillator strengths show that there are three relatively strong peaks at energies 0.63, 4.04, and 5.49 eV, which correspond to the transitions 12Σ+ → 12Π, 12Σ+ → 22Π, and 12Σ+ → 22Σ+, respectively. Additionally, the electronic configuration and the harmonic vibration frequencies of each state are also investigated.

Effect of protonation on the ground state properties of retinal analogs: an ab-initio study

1987 ◽  
Vol 65 (4) ◽  
pp. 892-897 ◽  
Author(s):  
Raymond A. Poirier ◽  
Arpita Yadav ◽  
Péter R. Surján
Keyword(s):  
Schiff Base ◽  
Ground State ◽  
Atomic Charge ◽  
Bond Orders ◽  
Bond Lengths ◽  
Ground State Properties ◽  
Cis And Trans Isomers ◽  
Base Analog ◽  
Retinal Analogs ◽  
Cis And Trans

The ground state properties (bond lengths, bond orders, net atomic charge distribution) of various cis and trans isomers of retinal analogs have been studied at abinitio SCF and correlated levels. The effect of protonation on the properties of the retinal Schiff base analogs has also been studied. Convergence in various properties has been observed with increasing chain length justifying the use of smaller analogs mimicking retinal. Convergence is, however, slower for the protonated retinal Schiff base analogs. The protonated retinal Schiff base analogs show an increased conjugation reflected in the bond orders, bond lengths, and in the decrease in the HOMO–LUMO gap. The nodal characteristics of the HOMO of the protonated retinal Schiff base analog also indicate a strong conjugation in the vicinity of the protonated nitrogen. Based on the results of calculations at the correlated level, the sudden polarization charge transfer mechanism is shown to be an artifact of HF-based methods used in the calculations.

Multireference calculations of potential energy and transition dipole moment surfaces for first and second UV absorption bands of N2O

2014 ◽  
Vol 13 (02) ◽  
pp. 1450020
Author(s):  
Mohammad Noh Daud
Keyword(s):  
Dipole Moment ◽  
Potential Energy ◽  
Excited States ◽  
Transition Dipole Moment ◽  
Basis Set ◽  
Conical Intersections ◽  
Excitation Energies ◽  
Absorption Bands ◽  
Transition Dipole ◽  
Vertical Excitation

A great deal of theoretical work has been carried out to investigate the properties of the six lowest singlet electronic states of N 2 O molecule: the ground state X 1A′; the excited states 11A′′, 21A′, 21A′′, 31A′ and 31A′′. Multireference configuration interaction (MRCI) approach has been used to compute the full-dimensional potential energy surfaces of the six lowest states employing aug-cc-pVQZ minus g orbital basis set. It was found that such of highly accurate potential yields excellent results of bond dissociation and vertical excitation energies in comparison with the experimental values. Several important symmetry and nonsymmetry related conical intersections in linear and bent geometries have been discussed. Of particular interest is the location of conical intersections between the 21A′(1Δ) and 31A′(1Π) states, and between the 11A′′(1Σ-) and 31A′′(1Π) states in linear geometry, as well as conical intersection between the X 1A′ and 21A′ states in bent geometry. The corresponding transition dipole moment surfaces have also been computed, connecting the ground electronic state to the lowest five excited states. Detailed discussion on the vector properties of the dipole transition has been presented specifically in the vicinity of the conical intersections.

Microwave Spectrum of γ-Thiobutyrolactone

1982 ◽  
Vol 37 (2) ◽  
pp. 129-133 ◽  
Author(s):  
José L. Alonso ◽  
J. C. Lopez ◽  
F. Mata
Keyword(s):  
Dipole Moment ◽  
Excited States ◽  
Ground State ◽  
Stark Effect ◽  
Potential Energy Function ◽  
Microwave Spectrum ◽  
Average Intensity ◽  
Vibrational States ◽  
Bending Vibration ◽  
Out Of Plane

Abstract The microwave spectrum of γ-thiobutyrolactone has been observed and measured in the vibra-tional ground state and in several excited states of the ring-bending and ring-twisting modes. From the value of the μc component of the dipole moment and inertial-defect considerations the ring skeleton was shown to be non-planar. The average intensity ratio for the rotational transitions between the ground and excited vibrational states indicates that the first excited state of the ring-bending and ring-twisting modes are ~ 120 cm-1 and ~ 250 cm-1 above the ground state respectively. These two out-of-plane ring vibrations are essentially independent and the ring-bending vibration is governed by a nearly harmonic potential energy function. The components of the dipole moment were determined by the Stark effect to be μa = 3.770 ± 0.001 D, μb = 1.818 ± 0.044 D and μc = 0.832 ± 0.018 D, leading to μtotal = 4.268 ± 0.023 D. The rigidity of the γ-thiobutyrolactone ring is discussed in relation to those of related molecules.

Experimentelle und Quantenchemische Untersuchungen der Dipolmomente von Substituierten Stilbenen im Ersten Angercgten Singulettzustand / Experimental and Quantum Chemical Investigations of Dipole Moments of Substituted Stilbens in the First Excited Singlet State

1977 ◽  
Vol 32 (5) ◽  
pp. 420-425 ◽  
Author(s):  
A. Kawski ◽  
I. Gryczyński
Keyword(s):  
Dipole Moment ◽  
Excited States ◽  
Ground State ◽  
Quantum Chemical ◽  
Singlet State ◽  
Dipole Moments ◽  
Excited Singlet State ◽  
Excited Singlet ◽  
Fluorescent State ◽  
Experimental Values

Abstract The values a/a3 (α = polarizability), the Onsager cavity radii a and the dipole moments μe of six substituted stilbens in the fluorescent state have been determined. It is shown that if the dipole moment of the lowest excited singlet state μe is parallel to the dipole moment in the ground state μg, the values of μe and a can be determined from the solvent effects. Moreover, quantum chemical investigations of the dipole moments in the ground and excited states were carried out with the Pariser-Parr-Pople method and compared with the experimental values.

Theoretical and Experimental Investigation on Dipole Moment of Synthetized yt-Base in the Ground and Excited States

1979 ◽  
Vol 34 (2) ◽  
pp. 172-175 ◽  
Author(s):  
I. Gryczyński ◽  
Ch. Jung ◽  
A. Kawski ◽  
S. Paszyc ◽  
B. Skalski
Keyword(s):  
Experimental Investigation ◽  
Dipole Moment ◽  
Excited State ◽  
Excited States ◽  
Ground State ◽  
Fluorescence Spectra ◽  
Dipole Moments ◽  
Aprotic Solvents ◽  
Absorption And Fluorescence Spectra ◽  
First Excited State

Abstract The electric dipole moment of yt-Base calculated by the CNDO/S and JNDO/S method is μg = 3.42 D and μg = 3.74 D in the ground state and μe = 4.41 D and μe = 5.67 D in the first excited ππ*-state, respectively, μg and μe being nearly antiparallel. Measurements of absorption and fluorescence spectra of yt-Base in aprotic solvents of different polarity yielded μg = 3.8 D and μe = 4.3 D and the directions of dipole moments were found to be nearly antiparallel.This comparison may be considered as an indication for the ππ* character of the observable first excited state, although the CNDO/S-and JNDO/S-calculations predict a nπ*-state as the lowest lying excited state

N.M.R.-Studies of Bond Order in Azulene, Biphenylene and 1,6-Methano[10]annulene

1990 ◽  
Vol 43 (9) ◽  
pp. 1541 ◽  
Author(s):  
MJ Collins ◽  
S Sternhell ◽  
CW Tansey
Keyword(s):  
Experimental Data ◽  
Ground State ◽  
Bond Order ◽  
Membered Ring ◽  
Coupling Constants ◽  
Bond Orders ◽  
Bond Lengths ◽  
Theoretical Predictions ◽  
Electron Distributions ◽  
Good Agreement

The 4J(H-C-C-Me) coupling constants of methyl-substituted derivatives, probes of bond order, have been used to examine the ground-state π- electron distributions in azulene (1), biphenylene (2) and 1,6- methano [10] annulene (3). The experimental data obtained are in good agreement with theoretical predictions for biphenylene (2) and provide some evidence for π-electron disproportionation towards the five-membered ring in azulene (1). The bond orders in 1,6-methano [10] annulene (3) obtained in this work are at variance with those predicted on the grounds of bond lengths.

Calculation of static molecular properties in the framework of the unitary group based coupled cluster approach

1996 ◽  
Vol 74 (6) ◽  
pp. 918-930 ◽  
Author(s):  
Josef Paldus ◽  
Xiangzhu Li
Keyword(s):  
Dipole Moment ◽  
Finite Field ◽  
Ground State ◽  
Unitary Group ◽  
Linear Response ◽  
Molecular Properties ◽  
Basis Set ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Static Properties

The recently developed and implemented state selective, fully spin-adapted coupled cluster (CC) method that employs a single, yet effectively multiconfigurational, spin-free reference and the formalism of the unitary group approach (UGA) to the many-electron correlation problem, has been employed to calculate static electric properties of various open-shell (OS) systems using the finite field (FF) technique. Starting with the lithium atom, the method was applied at the first-order interacting space single and double excitation level (CCSD(is)) to several first- and second-row hydrides having OS ground state, namely to the CH, NH, OH, SiH, PH, and SH radicals. In the case of NH we also considered three OS excited states. In all cases the dipole moment and polarizability were determined using a high quality basis set and compared with the experiment, whenever available, as well as with various configuration interaction results and other theoretical results that are available from the literature. The agreement of our CCSD(is) values with experiment is very satisfactory except for the 3Σ− ground state of the NH radical, where the experimentally determined dipole moment is too small. No experimental data are available for the corresponding polarizabilities. It is also shown that the FF technique is not suitable for calculations of higher order static properties, such as the hyperpolarizability β and γ tensors. For this reason we formulate the linear response version of our UGA-based CCSD approach and discuss the aspects of its future implementation. Key words: static molecular properties, dipole moments, polarizabilities, free radicals, unitary group based coupled cluster method, linear response theory, finite field technique.

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