Electric dipole moment of the diatomic AgBr molecule

Stark effect measurements on hyperfine components of the J = 3 – 2 rotational transition of ¹⁰⁷ Ag ⁷⁹ Br and ¹⁰⁹ Ag⁷⁹ Br at 11.5 GHz were carried out. The electric dipole moment derived for AgBr in its ground electronic and vibrational state is |μ_o| = 5.620 ± 0.030 D.     

Electric dipole moment of the diatomic if molecule

The electric dipole moment of the IF molecule has been determined by a study of the Stark effect on the hyperfine components of the J = 1 ← 0 rotational transition lying in the 17 GHz region. The production of molecules was by microwave discharge of I₂ and C₆F₁₀(CF₃)₂. A direct diagonalisation of the energy matrix of the total hamiltonian has been used and the electric dipole moment derived for the ground vibrational state of IF is |μ₀ |= 1.948(20)D.     

Electric dipole polarity of diatomic molecules

The restricted SCF (single-configuration SCF) and MCSCF (multiconfiguration SCF) calculations are performed to compute the ground-state electric dipole moments of four pairs of diatomic molecules—(1) CO and BF; (2) SiO and AlF; (3) CS and BCl; and (4) SiS and AlCl—at a number of internuclear distances on both sides of the equilibrium position. Near Hartree–Fock accuracy is obtained in the SCF calculations. All eight molecules have a range of internuclear distance in which electric dipole moments are of the polarity of A^?B⁺. The shapes of computed electric dipole moment functions are discussed in the language of the molecular orbital method and in relationship to electronegativities of atoms. The present study gives us deeper understanding of electron transfer inside molecules and consequently of the apparent contradiction between electronegativity and the dipole polarity of some molecules. © John Wiley & Sons, Inc.     

Electric dipole moment of BrCl

The electric dipole moment of the BrCl molecule has been determined by a study of the Stark effect on nine hyperfine components of the J = 1 ← 0 rotational transition lying at 9 GHz. A direct diagonalisation procedure of the energy matrix of the total hamiltonian has been used and the electric dipole moment derived for the ground vibrational state of BrCl is |μ_o| = 0.519 ± 0.004 D.     

On the relation between the non-adiabatic vibrational reduced mass and the electric dipole moment gradient of a diatomic molecule

The relation between the non-adiabatic vibrational correction to the reduced mass, i.e. the vibrational g-factor, and the electric dipole moment gradient of a diatomic molecule is investigated. An explicit expression for the “irreducible” non-adiabatic contribution in terms of excited electronic states is derived. The importance of this expression for the analysis of vibration-rotational spectra of diatomic molecules is discussed and explicit expressions are presented for the first two fitting parameters in an expansion of the non-adiabatic vibrational term in an effective vibration-rotational Hamiltonian. Results of ab initio multiconfigurational self consistent field calculations of the non-adiabatic contribution to vibrational g-factor of hydrides and fluorides of Li, B, Al, Ga and monoxides of C, Si and Ge are presented and compared with the corresponding non-adiabatic contributions to the rotational g-factor.     

Continued fraction representations of the dipole moment function and the electronic transition moment function of diatomic molecules

Explicit consideration of the X² Π state of OH and the X¹Σ⁺ state of HF is used to demonstrate that continued fraction approximations provide particularly good representations to the dipole moment functions and allow for extrapolation outside the region for which data is available. Continued fractions also prove useful for representing other molecular properties which are functions of the internuclear separation. As a second example a study of the B¹Σ_u^÷ ? X¹Σ_g⁺ electronic transition of H₂ is included.     

Stark effect,polarizabilities and the electric dipole moment of heteronuclear diatomic molecules in 1Σ states

The theory of second-order Stark effect in ¹Σ states of heteronuclear diatomic molecules is thoroughly reviewed. The rigorous treatment given demonstrates that by introducing rotational, vibrational and electronic branch polarizabilities, the intrinsic character of the second-order Stark effect in diatomic molecules can be shown to be related more closely to polarizabilities than to dipole moments. The well-known expression for the Stark shift in ¹Σ levels which is dominated by the square of the dipole moment is only a crude, though sufficient approximation whenever large dipole moments are involved. For small dipole moments, however, this approximation is likely to fail, leading to an erroneous determination of such dipole moments. In the limiting case of negligible influence of the molecular rotation on the vibronic matrix elements, the arithmetic mean of the electronic branch polarizabilities turns out to be equal to the well-known static electronic polarizabilities α_∥ and α_⊥. The results are applied to the interpretation of the Stark splitting in the A¹Σ⁺, υ′ = 5, J′ = 1 level of ⁷LiH, recently determined by Stark quantum-beat spectroscopy.     

Electronic ground states and vibrational frequency shifts of diatomic ligands in heme adducts

DFT calculations were carried out to study heme complexes with diatomic ligand (CO, NO, or O(2)) and trans-imidazole ligand. The optimized electronic ground states of CO, NO, and O(2) adducts are singlet, doublet, and open-shell singlet, respectively. For O(2) adduct, the open-shell singlet is slightly lower in energy than the close-shell singlet. However, important differences are found in optimized structures and vibrational frequencies. Particularly, the trans-imidazole-induced frequency up-shift of the Fe-O(O) stretching mode can be predicted only with the open-shell singlet as ground state. An analysis of normal modes confirms that the up-shifts in the bent (NO and O(2) ) adducts are mainly due to mixing of Fe-X(O) stretching mode with Fe-X-O bending coordinate. Our study of binding mechanism indicates that a secondary source of the upshifts is the diminished weakening of the Fe-X(O) bonds. The Fe-X(O) bond strengths are modulated by σ competition mechanism, which weakens the Fe-X(O) bond and σ-π cooperation mechanism, which only exists in the bent adducts and enforce the Fe-X(O) bond. -     

Highly accurate potential-energy and dipole moment surfaces for vibrational state calculations of methane

Full-dimensional ab initio potential-energy surface (PES) and dipole moment surface are constructed for a methane molecule at the CCSD(T)/cc-pVTZ and MP2/cc-pVTZ levels of theory, respectively, by the modified Shepard interpolation method based on the fourth-order Taylor expansion [MSI(4th)]. The reference points for the interpolation have been set in the coupling region of CH symmetric and antisymmetric stretching modes so as to reproduce the vibrational energy levels related to CH stretching vibrations. The vibrational configuration-interaction calculations have been performed to obtain the energy levels and the absorption intensities up to 9000 cm(-1) with the use of MSI(4th)-PES. The calculated fundamental frequencies and low-lying vibrational energy levels show that MSI(4th) is superior to the widely employed quartic force field, giving a better agreement with the experimental values. The absorption bands of overtones as well as combination bands, which are caused by purely anharmonic effects, have been obtained up to 9000 cm(-1). Strongly coupled states with visible intensity have been found in the 6500-9000 cm(-1) region where the experimental data are still lacking.     

The rotational and vibrational spectra,structure and dipole moment of 1,3-dioxole-2-thione

Rotational and centrifugal distortion constants are determined for the ground state and several excited states of the lowest vibrational mode of l,3-dioxole-2-thione, the “envelope” ring-bending mode. The structure of the molecule is planar. The A-constant is 1% larger than that of 1,3-dioxole-2-one (vinylene carbonate), which indicates small changes in ring-geometry on substituting CS for CO. The dipole moment of 1,3-dioxole-2-thione deduced from Stark-effect measurements is (1.60 ± 0.02) × 10^?29 Cm (4.81 ± 0.06 D). IR and Raman spectra lead to a complete analysis of the normal modes of vibration, based partially on a normal coordinate calculation.     

Theoretical study with rovibrational and dipole moment calculation of sextet states of the CrCl molecule

The potential energy curves have been investigated for the 13 lowest sextet electronic states in the representation below 53,000 cm^?1 of the molecule CrCl via CASSCF and MRCI (single and double excitation with Davidson correction) calculations. The harmonic frequency ω_e, the internuclear distance r_e, the rotational constant B_e, the electronic energy with respect to the ground state T_e, and the permanent dipole moment μ have been calculated. By using the canonical functions approach, the eigenvalues E_v, the rotational constant B_v, and the abscissas of the turning points r_min and r_max have been calculated for the considered electronic states up to the vibrational level v = 16. Nine electronic states have been studied theoretically here for the first time. The comparison of these values with the theoretical and experimental results available in the literature shows a good agreement. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

On the origin dependence of the angle made by the electric and magnetic vibrational transition dipole moment vectors

The concept of robustness of rotational strengths of vibrational modes in a VCD spectrum has been introduced as an aid in assignment of the absolute configuration with the help of the VCD spectrum. The criteria for robustness have been based on the distribution around 90° of the angles ξ(i) between electric and magnetic transition dipoles of all the modes i of a molecule. The angles ξ(i) (not, of course, the rotational strengths) are, however, dependent on the choice of origin. The derived criteria are for the center of mass chosen as the origin of the coordinate system. We stress in this note that application of the derived criteria assumes that excessive translation of the coordinate origin is not applied. Although the ξ(i) angles are not very sensitive to the position of the origin, very small displacements (a few ?) are not a problem, excessive translation of the origin does have considerable effect on the ξ(i) angles. In this note we quantify this effect and demonstrate how the distribution of ξ(i) angles is affected. Although it is possible to recalibrate the robustness criteria for the angles for a specific (large) displacement, we recommend that such displacement simply be avoided. It is to be noted that some modeling software does yield output with excessively displaced coordinate origin; this should be checked and corrected.     

Squeezing the ground vibrational state of diatomic molecules

We study the squeezing of minimal width vibrational wave packets of diatomic molecules, like Na₂, by using several laser schemes that couple the ground and excited electronic configurations of the molecule. The different schemes imply diabatic and adiabatic laser transformations, or a combination of both, whose efficiency and required physical resources are compared and analyzed.     

Electronic structure with a dipole moment calculation of the low-lying electronic states of the KHe molecule

The KHe molecular system is extensively studied by multi-reference configuration interaction calculations. Potential energy curves are constructed for 20 lowest electronic states, and molecular parameters are extracted. A comparison of our results with previous works shows remarkable agreement. A further calculation of the dipole moment functions through a wide range of the internuclear separation is performed and their corresponding curves are presented. Charge transfer is detected from the change in the sign of these functions particularly for R < R _e. Negative dipole moment values near R _e are predicted for 3 excited states, (1)²Π, (3)²Σ⁺ and (1)⁴Π, which are of a relatively short-range strong-binding nature. On the other hand, weakly binding long-range excited states predict positive values of the dipole moment near R _e reflecting the K^–He⁺ polarity.     

On the preference for vibrational energy in diatomic dissociation

Recent measurements of dissociation and relaxation rates, and of dissociation induction times, are shown to indicate very serious depletion of vibrational state populations during thermal dissociation. The large measured dissociation rates are then only compatible with dissociation from low vibrational states, i.e., there can be at most a very weak bias favoring vibrational excitation in thermal dissociation. It is suggested that dissociation from low vibrational states is assisted by rotational excitation.     

Calculation of vibrational constants of diatomic molecules

We apply Wigner's effective-harmonic-oscillator (EHO) function with the Morse potential to the calculation of vibrational constants of diatomic molecules. A one-particle system is described by the operator representation of Wigner's function. We find the EHO parameters both for a single molecule and for an equilibrium ensemble of molecules. We obtain numerical values of the constants for the iodine molecule.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 4, pp. 485–487, July–August, 1988.     

Design of UV laser pulses for the preparation of matrix isolated homonuclear diatomic molecules in selective vibrational superposition states

The preparation of matrix isolated homonuclear diatomic molecules in a vibrational superposition state c0Phie=1,v=0+cjPhie=1,v=j, with large (|c0|2 approximately 1) plus small contributions (|cj|2<1) of the ground v=0 and specific v=j low excited vibrational eigenstates, respectively, in the electronic ground (e=1) state, and without any net population transfer to electronic excited (e>1) states, is an important challenge; it serves as a prerequisite for coherent spin control. For this purpose, the authors investigate two scenarios of laser pulse control, involving sequential or intrapulse pump- and dump-type transitions via excited vibronic states Phiex,k with a dominant singlet or triplet character. The mechanisms are demonstrated by means of quantum simulations for representative nuclear wave packets on coupled potential energy surfaces, using as an example a one-dimensional model for Cl2 in an Ar matrix. A simple three-state model (including Phi1,0, Phi1,j and Phiex,k) allows illuminating analyses and efficient determinations of the parameters of the laser pulses based on the values of the transition energies and dipole couplings of the transient state which are derived from the absorption spectra.     

Electric π dipole polarizabilities in the ground and first excited singlet states of N-retinylidene derivatives

Ground and first excited singlet state electric π dipole polarizabilities for a set of 23 N-retinylidene derivatives are reported. The calculations are made by means of second order perturbation theory with Hückel state functions as a basis.     

Role of the electric dipole moment in positron binding to the ground and excited states of the BeO molecule

Self-consistent-field and multireference single- and double-excitation configuration interaction (CI) calculations have been carried out for various electronic states of the beryllium oxide molecule and their positron-attached counterparts. Particular emphasis is placed on the correlation between the polarity of a given BeO state and the magnitude of the positron binding energy as the internuclear distance is varied. Potential curves are computed for all BeO states that correlate with the first three atomic limits for this system and good agreement is found between the experimental and calculated spectroscopic constants in all cases. The present level of CI treatment is known to underestimate the positron affinities of atoms by at least several tenths of an eV, and this fact needs to be taken into account in evaluating the results for positron binding to molecules. The lowest BeO excited states (3,1Pi) are not found to bind with a positron in the Franck-Condon region due to their comparatively small dipole moments caused by O to Be charge transfer relative to the X 1Sigma+ ground state, which in turn does have a fairly sizeable positron affinity. The situation changes significantly as dissociation proceeds, however, with both 4,2Pi and 2Sigma+ positronic states lying several tenths of an eV lower than their neutral counterparts over a broad range of internuclear distance.     

Effects of rotation on vibrational relaxation in diatomic molecules

An approximate method is presented for allowing for the effects of rotation on the rate of vibrational relaxation in a diatomic molecule; this is based on local separation of the variables in the interaction region. An interpretation is given for experiments on the vibrational relaxation of HI in a shock wave.