Asymmetric Potential Energy Research Articles

Microwave rotational spectrum, electric dipole moment and geometry of 2-bicyclo[3.1.0] hexanone

We report the microwave rotational spectrum of 2d̄bicyclo[3.1.0]hexanone in its vibrational ground state and in vibrationally excited states associated with the bending mode ν B of the five-membered ring. Variation of the rotational constants with ν B allows the conclusion that the five-membered ring is effectively planar although the mode v B is governed by an asymmetric potential energy function. Measurement of teh Stark effect in a number of transitions leads to the components μ α = 3.28 ± 0.02 D and μ b = 1.81 ± 0.2 D of the electric dipole moment.

Charge transfer between two immiscible electrolyte solutions: Part IX. Kinetics of the transfer of choline and acetylcholine cations across the water/nitrobenzene interface

Kinetic and thermodynamic parameters of the transfer of choline and acetylcholine cations across the water/nitrobenzen interface were evaluated using convolution potential sweep voltammetry. In order to trace the factors which control the ion-transfer kinetics the semi-phenomenological theory was used, assuming that: (1) the temperature dependence of the rate constant has the form of the Arrhenius equation; (2) the reaction site is located in the outer Helmholtz plane (oHp); (3) there exists a Brønsted-type relationship between the true activation Gibbs energy and the reaction Gibbs energy for the ion transfer from the oHp in water to that in the organic solvent phase. The apparent rate constants were corrected for the double-layer effect using the capacity data and the Gouy-Chapman theory. It is concluded that the observed potential dependence of the apparent rate constants arises largely from the effect of the potential on the concentration of the transferred ions at the reaction planes. The correlation of the true (corrected) rate constant with the reaction Gibbs energy for a series of the ions with similar structure indicates that the true charge-transfer coefficient α 1≅0.3, which would correspond to the asymmetric potential energy barrier for the ion-transfer step.

Two-dimensional analysis of the ring-puckering and PH inversion vibrations of 3-phospholene

The ring-puckering energy levels for 3-phospholene, CH2CH=CHCH2PH, in both the ground and excited states of the PH inversion vibration have been established from the vibrational spectra of this molecule. The availablity of such extensive data made it possible to determine a reliable two-dimensional (with the ring-puckering and the P–H inversion as the two coordinates) potential energy surface. For the calculations, the kinetic energy coefficients g44, g55, and the cross term g45 were accurately represented as functions of both coordinates. An initial approximation to the asymmetric two-dimensional potential energy surface was obtained from the one-dimensional ring-puckering function as well as from structural data from microwave spectroscopy. Symmetry constraints established which potential terms were to be utilized. Three separate computer programs were written in order to calculate the vibrational energy levels and to adjust the potential parameters. The most efficient approach utilized a product of two prediagonalized basis sets for the basis functions. Initial attempts to fit the data with a potential surface using terms up through fourth power proved unsatisfactory in fitting data for the inversion excited state. A local solution based on Van Vleck perturbation theory was thus obtained and then expanded, using the symmetry constraints, to the entire solution. The resulting potential surface, which required the use of sixth power terms, gave excellent agreement with the observed spectra. Only five variable parameters were adjusted (for the local solution) in order to fit the 20 observed frequencies. The final potential surface has a central barrier of about 5500 cm−1 for the planar configuration. The more stable endo conformation lies 785 cm−1 in energy below that of the exo form with similar puckering angle (18°).

The temperature effect on the OH stretching vibration band of hydrogen bonded complexes

The temperature effect on the infrared spectra of hydrogen bonded systems has been analysed in terms of a stochastic model. Two different sources of this effect on protonic vibration bands have been shown. For weaker hydrogen bonds with an asymmetric potential energy curve the main factor seems to be a lowering of the average bridge length with decreasing temperature. Numerical results regarding the coefficient dν OH/d T are in good agreement with experiment. In the case of moderately strong symmetric hydrogen bonds the main factor seems to be a population change of split tunnelling levels.

Low-frequency vibrational spectra and conformations of bicyclo [3.2.0] hept-6-ene and 2-oxabicyclo [3.2.0] hept-6-ene

The low-frequency (100–500 cm−1) infrared and Raman spectra of bicyclo [3.2.0] hept-6-ene and its 2-oxa analog have been analyzed. The large collection of transitions involving the four out-of-plane ring modes were assigned and complex interaction was found. For the oxa compound a detailed energy level diagram was determined from the 30 transitions observed. Analysis of the ring-puckering spectra demonstrated that the asymmetric potential energy functions had only one energy minimum within 4 kcal/mole of the ground state, which corresponds to a boat species. Whether a second minimum is present at higher energies could not be determined.