Calculation Of Dipole Moment Derivatives Research Articles

Dipole function for the C-H oscillator

Using local mode description for methyl chloride, the infrared intensities for the first four CH3 stretching overtone bands are used to calculate the dipole function for the C-H bond. Detailed expressions for overtone transitions for diatomic molecules derived by Bouanich are employed for the calculation of dipole moment derivatives.

Analytical representations of atomic partial charges and charge fluxes in dissociating systems

Atomic partial charges and their changes along dissociating coordinates are investigated in the model systems HF, [HF⋯H] +, H 2O, H 3O +, H 2O⋯HOH and [H 2O⋯H⋯OH 2] +. Ab initio calculations of dipole moment derivatives as computational observables representing the partial charges are presented. The results are fitted with an analytic distribution function of atomic partial charges that can capture the opposing limiting behaviors of dissociating X-H bonds in both protonated and unprotonated cases. Specifically, it is found that a Fermi-Dirac type distribution function provides a reasonable economical representation for charge transfer across bonds. Atom types in dissociating systems are necessarily variables and an appropriate atom type function is introduced as a parameter of the analytic charge distribution function.

The analytic evaluation of second-order møller-plesset (MP2) dipole moment derivatives

An efficient vectorised procedure for the calculation of dipole moment derivatives at the closed-shell MP2 level of accuracy is described. The formalism for the calculation of MP2 gradients is also given as it is shown that the dipole moment derivatives can be handled in a very similar manner. Examples are given for H 2O, HCN and H 2CO using a wide range of basis sets.

Transition dipole interaction in polypeptides: Ab initio calculation of transition dipole parameters

Ab initio calculations of dipole moment derivatives of a model system of N-methylacetamide hydrogen-bonded to two formamide molecules give values for amide I and amide II transition dipole moments consistent with those derived from observed band splittings in the spectra of polypeptides. Transition dipole coupling thus provides a reasonable mechanism for explaining these splittings.

Ab initio self-consistent field assignment of vibrational spectra of diimide, N 2H 2

The structures and complete force fields of cis- and trans-diimide (diazene) were calculated using STO 3G and 4–31G basis sets with different approximations. The force constants obtained from these SCF wavefunctions for the trans species are compared with the most reliable experimental force fields, which are critically examined. To more accurately define and resolve the vibrational spectrum of diimide, a calculation of dipole moment derivatives was also performed. The results suggest that the torsional frequency of N 2H 2 should lie above 1300 cm −1, certainly in the spectral region of 1600–1660 cm −1.

Band intensities in the infrared spectra of metal carbonyl complexes: Chromium, molybdenum and tungsten hexacarbonyls

The absolute integrated intensities for IR absorption bands of M(CO) 6 ( M = Cr, Mo, W) were measured. The calculations of dipole moment derivatives of the molecules were performed using a procedure suggested by L. S. Mayants and B. S. Averbukh. The effective atomic charges of M(CO) 6 are estimated and discussed.

CNDO calculation of dipole moment derivatives and infrared intensities of formaldehyde

The complete neglect of differential overlap (CNDO) approximate wavefunctions for formaldehyde have been applied to the calculation of the derivatives of the dipole moment with respect to the symmetry coordinates (∂p/∂Sj). Agreement between the calculated derivatives and the experimental values given by Hisatsune and Eggers for the A1 symmetry species is exceptionally good, permitting an interpretation of the experimental results in terms of electronic distributions in the molecule. The agreement for the B1 and B2 symmetry species is also very good except for the asymmetric in-plane CH bend. However, the theory successfully predicts that charge reorientation for this motion is quite different from that which occurs in the out-of-plane CH bend, so that these motions are represented by CH bond moments of opposite polarity. An analysis is given of the results in terms of derivatives with respect to internal coordinates (∂p/∂rk). Comparison of ∂p/∂rCO values from a series of X2CO molecules (and also with ∂p/∂rCS for X2CS molecules) reveals an interesting trend. An analysis of the various contributions to the calculated ∂p/∂rk values is presented, with an explanation of the calculated results for the out-of-plane bending coordinate ∂p/∂γ.

CNDO Calculation of Dipole Moment Derivatives and Infrared Intensities of C6H6 and C6F6

The dipole moment derivatives of C6H6 and C6F6 have been calculated using the complete neglect of differential overlap (CNDO) approximate molecular orbital theory. The calculated set of derivatives with respect to the symmetry coordinates (∂ p/∂ Sj) for the e1u species of C6H6 agrees remarkably well with the unique experimental set of derivatives determined from infrared intensity measurements and the normal coordinate analysis for C6H6 and its deuterated analogues. The success of the benzene calculation suggests that we may have confidence in the CNDO results for C6F6, even though the agreement with the experimental results is much worse. An analysis of the ∂ p/∂ Sj values is given in terms of bond moment derivatives. The failure of the CNDO theory to predict a sufficiently large ``rehybridization moment'' to explain the observed intensity difference between in-plane and out-of-plane bending vibrations is discussed.

On a new method for the calculation of dipole moment derivatives from infrared intensities

The recent method of Girljavallabhan, Joseph and Venkateswarlu for the calculation of dipole moment derivatives from infrared intensities is unsatisfactory because their matrix of intensity constants is not generally diagonalized by the normal coordinate transformation that diagonalizes the potential and kinetic energy matrices.