Dipole moments,transition moments,oscillator strengths,radiative lifetimes,and overtone intensities for CH and CH+ as computed by quasi-degenerate many-body perturbation theory

The correlated, size-consistent, ab initio effective valence-shell dipole operator (μ^v) method is used to calculate dipole moments and transition dipole moments of the CH molecule and transition dipole moments of the CH⁺ ion as a function of internuclear distance. The dipole and transition dipole moments computed here compare well with those of other accurate ab initio methods. The transition dipole moments are then used to calculate oscillator strengths and radiative lifetimes for the A → X and B → A transitions of the CH⁺ ion and the A → X transition of the CH molecule. Comparisons are made with the best available theoretical and experimental lifetimes. Finally, the CH ground-state dipole moment function is used to evaluate overtone intensities and to examine simple models of the CH overtone intensities in polyatomic molecules.     

A calculation of the isotropic and anisotropic spectral moments of the dipole oscillator strength distribution of N2

We calculate a range of isotropic and anisotropic spectral moments of the dipole oscillator strength distribution for N₂ in the random phase approximation. The internuclear dependence of, in particular, S∥(k) is nonnegligible and vibrationally averaged moments are reported. The results are compared to other calculations and to experiment when available, and we conclude that the scheme gives reliable results. Based on our results, we predict a 10% anisotropy in the stopping power of oriented N₂ molecules.     

Finite-field method calculations. IV. Higher-order moments,dipole moment gradients,polarisability gradients and field-induced shifts in molecular properties: Application to N2, CO,CN−, HCN and HNC

In this paper, theoretical methods developed in III are applied in calculating polarisabilities, polarisability gradients and field-induced shifts, by the finite-field method. Values of dipole moment gradients and higher-order moments, calculated from the unperturbed wavefunctions, are also reported. Results for N₂, CO, CN^?, HCN and HNC have been obtained at the SCF level; some CI results for the N₂ polarisability components and moments and for the dipole moment gradients of HCN are also given. The calculated polarisability gradients and dipole moment gradients have been used to estimate the Raman scattering intensities and depolarisation ratios and the IR absorption intensities. Model calculations of field-induced shifts in bond length, vibrational levels, spectroscopic constants, force constants and dipole moment gradient are reported for N₂ and CO.The discrepancy between the SCF and experimental bond dipole moment gradients for HCN, previously noted in the literature, has been re-examined and resolved by our CI results.     

An SCF-MS-Xα study of the bonding and nuclear quadrupole coupling in diatomic halogens and interhalogens in the ground X Σ and B Π 0 excited states

SCF-MS-Xα calculations of the electronic structure of diatomic halogens and interhalogens XY (X = I, Br, Cl; Y = I, Br, Cl, F) have been used to investigate the bonding and nuclear quadrupole coupling in these molecules. Calculations have been carried out for the ground X ¹ Σ electronic state, and for the excited B ³ Π₀ state in the case of I₂, Br₂, ICl and IBr. Good agreement (to within 10% in most cases) is obtained between the calculated and observed nuclear quadrupole coupling constants for the molecules in the ground state. For the excited state the agreement is not as good, but the calculation does reproduce the observed decrease in the coupling constants to less than one quarter of their ground state values, and analysis of the contributions to the field gradients clearly shows the reasons for this. The electric dipole moments and electric quadrupole moments of the molecules have also been calculated. However, these prove to be much more strongly dependent on the variables used in the calculation (atomic sphere radii, inclusion of d orbitals). The results of the calculations have also been used to test some of the assumptions made in the Townes and Dailey method of analysis of nuclear quadrupole coupling data.     

Molecular electric properties in electronic excited states: multipole moments and polarizabilities of H2O in the lowest1 B 1 and3 B 1 excited states

Summary The dipole and quadrupole moments and the dipole polarizability tensor components are calculated for the¹ B ₁ and³ B ₁ excited states of the water molecule by using the complete active space (CAS) SCF method and an extended basis set of atomic natural orbitals. The dipole moment in the lowest¹ B ₁ (0.640 a.u.) and³ B ₁ (0.416 a.u.) states is found to be antiparallel to that in the ground electronic state of H₂O. The shape of the quadrupole moment ellipsoid is significantly modified by the electronic excitation to both states investigated in this paper. All components of the excited state dipole polarizability tensor increase by about an order of magnitude compared to their values in the ground electronic state. The present results are used to discuss some aspects of intermolecular interactions involving molecules in their excited electronic states.     

Application of potential constants: Charge transfer and electric dipole moment change in the formation of heteronuclear diatomic molecules—IV

The harmonic and anharmonic potential (force) constants of heteronuclear diatomic molecules, which are usually available from normal coordinate analyses, are applied to problems of determining the number of electrons transferred (charge transfer) and electric dipole moment functions of such molecules. The approach developed here is mainly based on Slater's orbital expansion method, that is, in a non-spin-polarized calculation atomic energies in a molecule are expanded with respect to the occupation number of electrons of atomic orbitals. To confirm the accuracy and the reliability of the approach, we have calculated the number of electrons transferred and electric dipole moments for alkali halides and other heteronuclear diatomic molecules. Specially, detailed analyses of electric dipole moment functions have been carried out on hydrogen fluoride (HF) and hydrogen oxide (OH) for which reliable experimental dipole moment functions are presently known over a wide range of internuclear distances. It is concluded from these analyses that the present approach is simple and useful in evaluating the charge transfer and the dipole moment change in the formation of heteronuclear diatomic molecules.     

Influence of cation binding on the electro-optically determined electric moments of purple membranes

Analysis of the elect ro-optically determined permanent dipole moment and electric polarizability of purple membrane fragments reveals the complex nature of the membrane electric moments.The problem to distinguish between the contribution of the membrane structural charges (charged groups of the polypeptide chain and polar lipid headarouos), bound cations and the electric double layer structure deserves particular attention not only because of its importance for electro-optics but also in respect to the relation of the membrane surface electric properties to the membarans transport function.The removal of divalent cations (Ca²⁺ and Mg²⁺) bound to purple membrane in the native state induces a cat ion-free species or purple membrane (deionized - blue membrane) with drastically changed spectroscopic properties and function. The preseent paper summarizes our study on the electric moments of blue membrane and their changes during the blue to purple transition. We intended to provide an insight into the possible regulation of this reversible transition (purple-to-blue and blue-to-purple) through changes of the asymmetric charge distribution and the importance of the asymmetric interfacial charge distribution for the proton transfer in purple membranes.The changes in the electric moments (permanent and induced dipole moments) of purple membrane fragments upon di- and trivalent cations binding to cation-depleted purple membranes were studied by electric light scattering (rotational electrokinetics) in d.c. and a.c. electric fields, and by electric pulses with reversing polarity, the results show a recovery of the membrane charge asymmetry (permanent dipole moment) though not of the induced dipole moment.     

Hartree—Fock—Slater functions as basis for one-electron perturbation calculations for molecules: I. Calculation of ground state electric dipole polarizabilities

The analysis of the decoupling of Hartree—Fock—Slater SCF perturbation equations for an external field is undertaken. The points of departure from the corresponding Hartree—Fock perturbation equations are stressed. Both formal and numerical results suggest that the fully uncoupled Hartree—Fock—Slater expression is a less drastic approximation than the same Hartree—Fock one. The uncoupled expression for the ground state electric dipole polarizability is calculated for CO, N₂, ethylene, acethylene and trans-butadiene in the dipole length—dipole length, dipole velocity—dipole length and dipole velocity—dipole velocity alternative formulations with an ab initio Hartree—Fock—Slater SCF basis set. The results compare well with other non-empirical results and the dipole velocity-dipole length results are in remarkably good agreement with experiments.     

Spatial Taming and Trapping of Molecules

Molecular beam techniques for study of collisional and spectroscopic processes have recently been enhanced by use of static electric or magnetic fields to orient or align molecules with permanent dipole moments. A more general method is now in prospect, applicable both to alignment and to spatial trapping of molecules. This exploits the anisotropic interaction of the electric field vector of intense laser radiation with the dipole moment induced in a polarizable molecule by the laser field. The interaction creates directional superpositions of field-free states that correspond to oblate spheroidal wavefunctions, with eigenenergies that decrease with increasing field strength. We suggest that this polarizability interaction produces the marked alignment found in laser-induced dissociative ionization of CO by the Saclay group. We also present calculations illustrating the feasibility of spattal trapping. In combination with supermirror focussing and buffer-gas cooling, an intense infrared laser can typically confine molecules for long-times (-hours) within a small (-picoliter) and cold (?1°K) “pocket of light.”     

Ab initio study,including electron correlation,of the electronic structures,the dipole moments,the static polarizabilities and of the harmonic force fields of H2CO,H2CS and H2SiO

Ab initio calculations including electron correlation (on the PNO-CI and CEPA-PNO levels) are carried out for the isovalence electronic molecules H₂CO, H₂CS and H₂SiO, and for comparison also for H₂O and CO. The CEPA equilibrium distances are accurate to within 0.003 Å, while SCF results show significantly larger errors. The harmonic force constants on CEPA level are satisfactory as well, but for stretching of double or triple bonds inclusion of singly substituted configurations is imperative. Dipole moments were obtained with an error of 0.1 Debye from CEPA calculations with sufficiently large basis sets and inclusion of singly substituted configurations. The dipole polarizabilities are less sensitive to correlation effects but require larger basis sets.The population analysis reveals that the SiO bond in H₂SiO is highly polar and thatd-AO's cannot be regarded as valence AO's in any of the molecules of this study. The binding energy of H₂SiO (with respect to H₂Si(¹ A ₁) + O(³ P)) is predicted as 140 ± 5 kcal/mol. The contributions of different pairs in terms of localized orbitals to the correlation energy of the molecules of this study are analyzed.     

Permanent moment contributions to chiral discrimination

The discrimination energy, giving the difference in the interaction of two leavo molecules and one laevo with one dextro, is calculated where the coupling involves permanent electric and magnetic moments. Fixed electric dipoles arranged helically on a lattice (simulating the electric effects of a helical polymer for example) give chiral fields producing large (≈kT) discriminations. For the pairwise interaction of fixed molecules realistic electric dipole and electric quadrupole moments can lead to discriminations of about 100 cal mole^?1 at 0.5 nm separation. In the hypothetical case of molecules possessing permanent electric and magnetic moments it is four or more orders of magnitude less. In a freely rotating molecule pair the sequence is reversed and electric and magnetic dipoles give much the bigger averaged discrimination energy.     

Constrained self-consistent-field wave functions with improved long-range behavior

The recent suggestion that the long-range behavior of energy-optimized Gaussian basis sets can be improved by augmenting them with a Gaussian chosen to satisfy a constraint involving a linearly averaged position moment is explored. Calculations indicate that the high-order moments 〈r^k〉, with k > 4, in He, Be, and Li^?, and 〈x^kz^L?k〉, with L > 4 and k ≤ L, in H₂ are improved by the constraint, but that lower-order moments and dipole polarizabilities are not. In H₂, the higher moments with a given L improve by different amounts for different k, and, hence, the multipole moments do not improve. The basis-set superposition error in He? He and Be? Be interaction energy calculations decreases if the internuclear distance is large enough. Thus, the constraint procedure improves the very long range behavior of the self-consistent-field wave functions. © 1992 John Wiley & Sons, Inc.     

Principles for a direct SCF approach to LICAO–MOab-initio calculations

The principles and structure of an LCAO -MO ab-initio computer program which recalculates all two-electron integrals needed in each SCF iteration are formulated and discussed. This approach—termed “direct SCF ”—is found to be particularly efficient for calculations on very large systems, and also for calcuations on small and medium-sized molecules with modern minicomputers. The time requirements for a number of sample calculations are listed, and the distribution of two-electron integrals according to magnitude is investigated for model systems.     

Dynamic polarizabilities and raman intensities of CO,N2, HCl and Cl2

We have performed first-order (identical to coupled Hartree-Fock) and second-order polarization propagator calculations of the dynamic dipole polarizability tensor for the CO, N₂, HCl and Cl₂ molecules. The derivatives of the polarizability tensor with respect to the internuclear distance at the equilibrium internuclear separation are compared with related data obtained from non-resonance Raman spectra. In most cases the correlation contributions beyond the coupled Hartree-Fock approximation have a more pronounced effect on the derivatives of the polarizability tensor than on the polarizability tensor itself. At both levels of approximation we found that derivatives of the dynamic polarizability tensor with respect to the internuclear separation increase with 10–15% for variation of the frequency from 0 (static polarizability) to about 28500 cm^?1. The depolarization ratio calculated from the polarizability derivatives shows no variation with frequency in the same frequency range.     

Influence of heteroelement on dipole and quadrupole moments of a series of three-membered rings containing a second,third, fourth,or fifth-row atom: a theoretical investigation

The influence of heteroelements on the molecular dipole and traceless quadrupole moments of a series of twenty-two three-membered rings (1–22) was theoretically estimated employing levels of theory such as MP2, CCSD, and PBE1PBE in combination with standard Pople’s basis set. To an accurate evaluation of these properties, additional calculations on the optimized geometries were performed using the correlation-consistent cc-pVDZ and aug-cc-pVDZ basis sets on the three mentioned methods. In particular, the dipole and quadrupole moments from MP2 and CCSD approaches are comparable to each other for the studied molecules, while PBE1PBE calculations were significantly deviated compared to MP2 and CCSD levels. High level of theory and large basis sets seemed to be needed to obtain reliable electrical properties in the heterocycles containing heavy atoms. Results demonstrated that the dipole and quadrupole moments are strongly determined by the nature of the heteroatom into ring skeleton, and its magnitude depends on the polarity of C-heteroelement bond. Dipole moment of these molecules 1–22 showed a clear increase with the increase of electronegativity and the atomic size of heteroatom into ring skeleton. Then, high relative dipole moment was found for three-membered rings containing II, IIIA, VIA, and VIIA elements, which is associated to the high polarization of the C-heteroatom bond. A similar behavior was observed for the quadrupole moments of these three-membered rings.

     

Ab initio potential energy curves and transition dipole moments for the interaction of a ground state He with Na(3s–3p)

Potential energy curves of the states X ²Σ⁺, B (1)²Σ⁺ and A (1)²Π of the NaHe molecule have been calculated accurately in a large range of internuclear distances R from SA-CASSCF-MRCI calculations, using molecular orbitals expanded in cc-pV5Z basis sets. Transition dipole moments have also been calculated for the X–B, X–A and A–B transitions, in the same range of R. Their long-range behaviour have been considered.     

Ring opening of the molecular ion of 5(4H)-oxazolone

Quantum chemical calculations were carried out at several theoretical levels (semi-empirical, MNDO; ab initio, 3–21G SCF, 6–311G** SCF and DZP CISD) to investigate the ring-opening process of and the loss of CO from the molecular ion of 5(4H)-oxazolone. The ring-opening process is predicted to be slightly endothermic and the loss of CO from the open-ring molecular ion to be slightly exothermic. Detailed population analysis calculations suggest the weakening of the lactonic C? O bond in the closed-ring molecular ion and weak carbon—carbon and nitrogen—(formy)—carbon bonds in the open form. Both the open-ring molecular ion and the [M–CO]^+· ion are suggested to be of distonic type.     

Molecular properties of acetone and some of its chloroderivatives adsorbed at the surface of water

The relations between the electric surface potential (V) and the surface tension () of aqueous solutions of acetone, chloroacetone, 1,3-dichloroacetone, and their concentration were investigated. The vertical components of dipole moments of the above mentioned compounds were determined using the Helmholtz equation. The calculations were carried out on the basis of surface excess values, which were obtained from surface tension measurements and surface potential changes. Once the vertical component of dipole moments were found and the orientation of adsorbed molecules was assumed, the local dielectric permittivities of the surface monolayer were estimated.     

Influence of the chemical composition and comonomer distribution on the dipole moments of 3,3-dimethyloxetane/tetrahydrofuran copolymers

Experimental values of the dipole moment ratio 〈μ₂〉/nm² and its temperature coefficient d ln 〈μ₂〉²/dT, where 〈μ₂〉 is the mean-square dipole moment of a chain with n skeletal bonds and m² is the mean square of the skeletal bond dipole moments, are reported for well-characterized random copolymers of 3,3-dimethyloxetane and tetrahydrofuran. The results are interpreted in terms of the rotational isomeric state theory in a manner consistent with that developed for the parent homopolymers. The theory gives a good account of the experimental results corresponding to copolymers in which the mole fraction of tetrahydrofuran lies in the range 0.11–0.89. It is found that whenever the copolymerization obeys Bernouillan statistics, the dipole moments are quite insensitive to the comonomer distribution. The theoretical analysis suggests, however, that the value of the dipole moment ratio of alternating copolymers of 3,3-dimethyloxetane and tetrehydrofuran should be near that of the parent homopolymer of lower polarity.     

Theory of molecular optoelectronics. IX. Calculation of χ(2) from theoretical hyperpolarizabilities for DAN

Components of the crystal quadratic susceptibility tensor χ⁽²⁾ for second-harmonic generation are calculated for the title compound, 4-(N, N-dimethylamino)-2-acetamido-nitrobenzene. Input data are the crystal structure and refractive indices and CNDO hyperpolarizabilities; two different sets of refractive indices give similar results. The calculations yield effective polarizabilities as well as both rigorous and anisotropic Lorentz local electric fields. Susceptibility components are close to 10 pm V^?1, rather smaller than those deduced experimentally and showing a weaker dependence on direction; Kleinman symmetry is mostly observed within 10%. Screened dipoledipole interactions using CNDO dipole moments amount to ?80 kJ mol^?1, implying permanent fields of 2 GV m^?1.