Spectroscopic investigation of magnetic dipole allowed transitions through the magnetic transition moment

An experimental technique for detecting magnetic dipole allowed transitions by their dispersion-induced circular dichroism (DICD) is discussed. The DICD spectra of three nitrogen heterocycles (pyridine, pyrazine and tetraphenylporphyrin) are shown to be dominated by the n — π^* transitions, as distinct from the normal absorption spectra which are dominated by the electric dipole allowed π — π^* bands.     

On the evaluation of electric and magnetic dipole transition moments in the ZDO approximation

The implications of the ZDO approximation for the evaluation of electric and magnetic dipole transition moments are analyzed using an overlap ordered expansion of the type proposed by Fischer-Hjalmars. The relative merits of electric dipole length and electric dipole velocity matrix elements are discussed from the point of view of their use in conjunction with the ZDO approximation.

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Zusammenfassung Die Folgerungen aus der ZDO-Näherung für die Berechnung elektrischer und magnetischer Dipolübergangsmomente werden mit Hilfe einer geordneten Entwicklung der Überlappungsmatrix, wie von Fischer-Hjalmars vorgeschlagen, untersucht. Die relativen Vorzüge der Benutzung von Matrixelementen des Dipolmomentoperators einerseits und des Impulsoperators andererseits werden im Rahmen der ZDO-Näherung diskutiert.

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Résumé Analyse des implications de l'approximation du recouvrement différentiel nul dans l'évaluation des moments de transition dipolaire électrique et magnétique, en utilisant un développement en série selon les puissances du recouvrement du type de celui proposé par Fischer-Hjalmars. Les mérites relatifs des éléments de matrice des opérateurs longueur dipolaire électrique et vitesse dipolaire électrique sont discutés du point de vue de leur utilisation dans le cadre de l'approximation à recouvrement différentiel nul.

     

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.     

Efficient calculation of vibrational magnetic dipole transition moments and rotational strengths

A priori prediction of vibrational magnetic dipole transition moments and vibrational strengths requires the calculation of the overlap integral of the derivatives of the electronic wavefunction with respect to nuclear displacement and an external magnetic field. The efficient calculation of this integral, using coupled Hartree-Fock theory, is described.     

On the enhancement of the electric dipole moment in molecular complexes

In the formation of molecular complexes an enhancement Δμ of the molecular dipole moment with respect to the vectorial sum of the moments of the monomers is often observed. The charge distribution provided by infrared intensity studies successfully predicts, in several cases, Δμ as due to polarization effects.     

Nonplanarity of adenine: vibrational transition moment angle studies in helium nanodroplets

Mid-infrared spectra are reported for adenine monomer in helium nanodroplets. We show that there is only one tautomer of adenine, the global minimum structure, observed in helium nanodroplets and characterized by using ab initio calculations and the measurement of vibrational transition moment angles (VTMAs) for the various vibrational modes of the adenine monomer. On the basis of the VTMA analysis on the amino group of the global minimum tautomer, which gives insights into its nonplanarity, a detailed VTMA study of three lowest-energy amino tautomers of adenine is discussed in this study.     

Permanent electric dipole moment of molybdenum carbide

High resolution optical spectroscopy has been used to study a molecular beam of molybdenum monocarbide (MoC). The Stark effect of the R(e)(0) and Q(fe)(1) branch features of the [18.6] (3)Pi(1)-X (3)Sigma(-)(0,0) band system of (98)MoC were analyzed to determine the permanent electric dipole moments mu(e) of 2.68(2) and 6.07(18) D for the [18.6] (3)Pi(1)(nu=0) and X (3)Sigma(-)(nu=0) states, respectively. The dipole moments are compared with the experimental value for ruthenium monocarbide [T. C. Steimle et al., J. Chem. Phys. 118, 2620 (2003)] and with theoretical predictions. A molecular orbital correlation diagram is used to interpret the observed and predicted trends of ground state mu(e) values for the 4d-metal monocarbides series.     

Infrared laser spectroscopy of uracil and thymine in helium nanodroplets: vibrational transition moment angle study

Vibrational spectra are reported in the N-H stretching region for uracil and thymine monomers in helium nanodroplets. Each monomer shows only a single isomer, the global minimum, in agreement with previous experimental and theoretical studies. The assignment of the infrared vibrational bands in the spectra is aided by the measurement of the corresponding vibrational transition moment angles (VTMAs) and ab initio frequency calculations. The ambiguity in the VTMA assignment of the N3H band for the uracil monomer is explained by the presence of dimer bands, which are overlapped with the monomer band.     

The permanent electric dipole moment of calcium monodeuteride

The sub-Doppler laser induced fluorescence spectra of numerous branch features in the B 2Sigma+ -X 2Sigma+(0,0) band of calcium monodeuteride were recorded field-free and in the presence of a static electric field of up to 7 kV/cm. The field-free spectra were analyzed to produce an improved set of fine structure parameters for the B 2Sigma+(v=0) state. The observed electric field induced splittings and shifts were analyzed to produce permanent electric dipole moments of 2.57(3) and 2.51(3) D for B 2Sigma+(v=0) and X 2Sigma+(v=0) states, respectively. The permanent electric dipole moment for the X 2Sigma+(v=0) state of CaH is estimated to be 2.53(3) D.     

Discrepancy in the near-solute electric dipole moment calculated from the electric field

The electric dipole moment p ( r ) was computed as the integral of the permanent dipole moment of the solvent molecule μ( r ) weighted by the orientational probability distribution Ω( r ; O ) over all orientations, where O is the orientation of the solvent molecule at r . The relationship between Ω( r ; O ) and the potential of the mean torque was derived; p ( r ) is proportional to the electric field E ( r ) under the following assumptions: (1) the van der Waals (vdW) interaction is independent of the orientation of the solvent molecule at r ; (2) the solvent molecule and its electrical effect are modeled as a point dipole moment; (3) the solvent molecule at r is in a region far from the solute; and (4) μE( r ) ? k_BT, where k_B is Boltzmann's constant and T is absolute temperature. The errors caused by calculating near‐solute Ω( r ) and p ( r ) from E ( r ) are unclear. The results show that Ω( r ) is inconsistent with the value calculated from E ( r ) for water molecules in the first and second shells of solute with charge state Q = ±1 e, and a large variation in solvent molecular polarizability γ_mol(r), which appeared in the first valley of 4πr²E(r) for |Q| < 1 e. Nonetheless, p (r) is consistent with the values calculated from E (r) for |Q| ≤ 1 e. The implication is that the assumptions for calculating p ( r ) can be ignored in the calculation of the solvation free energy of biomolecules, as they pertain to protein folding and protein–protein/ligand interactions. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011     

Energetics and dipole moment of transition metal monoxides by quantum Monte Carlo

The transition metal (TM) oxygen bond appears very prominently throughout chemistry and solid-state physics. Many materials, from biomolecules to ferroelectrics to the components of supernova remnants, contain this bond in some form. Many of these materials' properties depend strongly on fine details of the TM-O bond, which makes accurate calculations of their properties very challenging. Here the authors report on highly accurate first principles calculations of the properties of TM monoxide molecules within fixed-node diffusion Monte Carlo and reptation Monte Carlo.     

Electric dipole moment of the diatomic tif in its higher vibrational states

The electric dipole moment of ²⁰⁵Tl¹⁹F has been measured in its higher vibrational states up to ν = 7 by studying the Statk effect in the J = O → 1 rotational transitions. The variation of the electric dipole moment with vibrational states is discussed. The electric dipole moment can be written as lμ_νl = 4.1941 (15) + 0.0681(12) (ν + $\text{1}\text{2}$) D.     

The electric dipole moment of iridium monofluoride, IrF

The P(5) branch features of the A (3)Φ(4)←X (3)Φ(4) (1,0) band near 628.2 nm of a molecular beam of iridium monofluoride, (193)IrF, were recorded field free and in the presence of a static electric field. The (193)Ir (I(1)=3/2) and (19)F (I(2)=1/2) hyperfine interactions in the A (3)Φ(4) (υ=1) and X (3)Φ(4) (υ=0) states were analyzed. The permanent electric dipole moments, μ(el), for the A (3)Φ(4) (υ=1) and X (3)Φ(4) (υ=0) states were determined to be 1.88(5) and 2.82(6) D, respectively, from the analysis of the observed Stark shifts. A comparison of the electric dipole moments for IrC, IrN, and CoF is presented.     

Ab initio vibrational transition dipole moments and intensities of formaldehyde

Vibrational transition dipole moments and absorption band intensities for the ground state of formaldehyde, including the deuterated isotopic forms, are calculated. The analysis is based on ab initio SCF and CI potential energy and dipole moment surfaces. The formalism derives from second-order perturbation theory and involves the expansion of the dipole moment in terms of normal coordinates, as well as the incorporation of point group symmetry in the selection of the dipole moment components for the allowed transitions. Dipole moment expansion coefficients for the three molecule-fixed Cartesian coordinates of formaldehyde are calculated for internal and normal coordinate representations. Transition dipole moments and absorption band intensities of the fundamental, first overtone, combination, and second overtone transitions are reported. The calculated intensities and dipole moment derivatives are compared to experiment and discussed in the context of molecular orbital and bond polarization theory.     

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.     

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 permanent electric dipole moment of chromium monodeuteride, CrD

A number of low-N lines of the X (6)Sigma(+)<--A (6)Sigma(+)(0,0) band of chromium monodeuteride, CrD, have been recorded at near the natural linewidth limit by high resolution laser excitation spectroscopy of a supersonic molecular beam sample. The shifts and splitting of these lines caused by a static electric field have been analyzed to give the permanent electric dipole moments of the X (6)Sigma(+)(upsilon=0) and A (6)Sigma(+)(upsilon=0) states as 3.510(33) and 1.153(3) D, respectively. The dipole moment of the A (6)Sigma(+)(upsilon=0) state can be measured with higher precision because of some interesting near degeneracies in its level structure. The trends in the observed dipole moments for the first-row transition metal monohydrides are rationalized and compared with theoretical predictions.     

Superpositions of chiral states in the presence of electric dipole, magnetic dipole, and electric quadrupole interactions

This paper is a straightforward generalization of Maierle-Harris proposal regarding parity implications on the superpositions of chiral states of a molecule. It is shown that the inclusion of electric quadrupole and magnetic dipole interactions removes several of restrictions on the preparation of superpositions of mid R:L and mid R:R states of a chiral molecule. It is also found that the dephasing of mid R:L and mid R:R superpositions, due to the spontaneous emission from the chiral molecule, has opposing contributions from electric quadrupole-magnetic dipole and electric dipole interactions.