Showing papers by "Poul Jo published in 1995"

Sign change of hyperpolarizabilities of solvated water

Abstract: The experimental work by Levine and Bethea [J. Chem. Phys. 65, 2429 (1976)] and by Ward and Miller [Phys. Rev. A 19, 826 (1979)] on the hyperpolarizability of solvated water and water in the gas phase, respectively, showed a very substantial effect of the solvent on the measured hyperpolarizability. The sign of the hyperpolarizability of solvated water changed compared to gas phase and the numerical value increased by a factor of 1.5. This article presents a theoretical investigation of the solvent effects of the hyperpolarizabilities and their frequency dispersions for liquid water using the continuum, semicontinuum, and supermolecular models. Calculations involving the semicontinuum and supermolecular models give the sign change of the hyperpolarizabilities, indicating that the hydrogen bonds and the static dipole interaction have substantial impact on the hyperpolarizability of liquid water. Hyperpolarizabilities calculated by the supermolecular approach are about one third of those calculated by the semi‐continuum model. The continuum and semicontinuum models involve a recent implementation of a quantum mechanical reaction field response method.

Electric field dependence of magnetic properties: Multiconfigurational self‐consistent field calculations of hypermagnetizabilities and nuclear shielding polarizabilities of N2, C2H2, HCN, and H2O

Abstract: Multiconfigurational self‐consistent field (MCSCF) response is used to study the electric field dependence of magnetizabilities and nuclear shielding constants for N2, C2H2, HCN, and H2O. London perturbation‐dependent atomic orbitals are used to ensure gauge origin independence. The computed magnetizabilities and shielding derivatives show a strong electron correlation dependence. The N2 results confirm the conclusions of previous ab initio studies. For the other molecules, this is the first study of the above magnetic properties beyond the SCF approximation.

Ab initio calculations of anharmonic vibrational circular dichroism intensities of trans‐2,3‐dideuteriooxirane

Abstract: A priori theory is derived for anharmonic calculations of vibrational circular dichroism (VCD). The anharmonic VCD expression is gauge origin independent and reduce to the magnetic field perturbation theory expression in the double‐harmonic approximation. The theory has been implemented using second‐order contact transformations for the vibration problem. Zeroth, first, and diagonal second derivatives of the atomic axial tensor are needed at the molecular equilibrium geometry. Ab initio calculations have been carried out for trans‐2,3‐dideuteriooxirane using self consistent field theory for the atomic axial tensors and using second‐order Mo/ller–Plesset theory for the atomic polar tensors and the force fields. The changes of the vibrational rotatory strengths from anharmonicities are small, and do not explain the previously observed large discrepancies between the double‐harmonic results and the experimental values for three out of the 15 vibrational modes.

Ab initio calculations of anharmonic vibrational transition intensities of trans‐2,3‐dideuteriooxirane

Abstract: The quartic force field and the cubic dipole moment surface are calculated for trans‐2,3‐ dideuteriooxirane at the self‐consistent field and the second order Moller–Plesset levels of theory using a triple zeta plus two polarization functions basis set. Contact transformation theory is used to determine the corresponding anharmonic vibrtional frequencies and intensities. Inclusion of anharmonicity improves agreement of the calculated frequencies and intensities with their experimental counterparts. The anharmonic corrections are much more sensitive to correlation effects for intensities than for frequencies.

A multiconfiguration self‐consistent‐field response study of one‐ and two‐photon dipole transitions between the X 1Σ+ and A 1Π states of CO

Abstract: The one‐ and two‐photon dipole transitions between the X 1Σ+ and the A 1Π states of CO have been studied by means of multiconfiguration self‐consistent‐field linear and quadratic response methods. The vibrationally averaged oscillator strength for the 0–0 one‐photon dipole transition between the X 1Σ+ and A 1Π states obtained using the linear response method is 1.31×10−2 as compared to the experimental results of 0.96(14)×10−2, 1.08(7)×10−2, and 1.11×10−2. The two‐photon transition probability rate constant, obtained using the quadratic response method, for the 0–1 vibrational band of the X–A transition of 7×10−59 cm4 s is more than six orders of magnitude smaller than the experimental result of 3.5×10−52 cm4 s. We suggest that the experiment should be reconsidered. The dipole moment of the A 1Π state obtained from quadratic response calculations on the ground state at R=2.332 a.u. is −0.0441 a.u. suggesting an anomalous polarity also for the A 1Π state. The experimental value is ±0.059(20) a.u.