Da‐Fei Feng

Classical trajectory study of the unimolecular decomposition of H–C≡C–Cl, H–C≡C–H, and Cl–C≡C–Cl

Monte Carlo rate constants and lifetime distributions for H–C≡C–H, H–C≡C–Cl, and Cl–C≡C–Cl at 200 kcal/mole were determined by classical trajectories. The Monte Carlo rate constants agree to within 30% of the RRKM prediction. Energy randomization is faster in Cl–C≡C–Cl than in H–C≡C–H and H–C≡C–Cl. An analysis of nonrandom lifetime distributions indicates that energy randomization is complete by 10−12 sec. for each of the molecules. Comparisons are made between our results and other unimolecular studies.

A semi-empirical estimate of the scattering cross section and mobility of excess electrons in liquid hydrocarbons

Abstract The scattering cross sections and intrinsic mobility of electrons in liquid hydrocarbons have been calculated from measurements of the quasi-free electron energy. By incorporating the mobility temperature dependence the calculated mobilities satisfactorily explain the tenfold difference of mobilities in n-hexane and neopentane.

Trajectory studies of unimolecular processes. II. Dynamics of chloroacetylene dissociation

Lifetime distributions for H–C≡C–Cl with respect to dissociation were determined at 200, 175, and 150 kcal/mole. Both random and nonrandom sampling techniques were used. An analysis of distributions of internal coordinate energies shows that vibrational energy redistribution is nearly complete within 4.5×10−13 sec. The results indicate that H–C≡C–Cl is an ’’intrinsic’’ RRKM molecule in the 200–150 kcal/mole energy domain.

Dynamics of ion solvation. Li++H2O→Li+(H2O)*

The classical trajectory method has been used to calculate the primary cross section for Li++H2O recombination versus relative translational energy. The criterion used for the formation of a vibrationally and rotationally excited Li+(H2O)* cluster is the presence of more than one inner turning point in the Li++H2O relative distance. As the relative translational energy is increased, there is a dramatic decrease in the primary cross section. It is 542 A2 at Erel = 0.5 kcal/mole and essentially zero at Erel = 5.0 kcal/mole. The results are discussed in terms of the inefficiency of intramolecular energy transfer from the Li++H2O relative motions to the H2O vibrational and rotational degrees of freedom.

Semicontinuum model for the trapped dielectron in polar liquids and solids

A semicontinuum model for trapped dielectrons, two electrons in the same cavity, has been developed and applied to liquid ammonia, water, ice at 77°K, and methyltetrahydrofuran and amine glasses at 77°K. In all matrices the configurational stability of the ground state of the dielectron has been established, and the dielectron is found to be stable with respect to two single trapped electrons. In general the cavity radius for the dielectron is slightly smaller than that for the single electron. The excited state of the dielectron is bound, and only slight shifts of the optical absorption band of the dielectron compared to the single electron are predicted.

Microdipole model for trapped electrons in nonpolar liquids and glassy solids

A model is developed to treat the binding energy of excess electrons in nonpolar liquids and solids such as alkanes. Interaction of the excess electron with C–H bond dipoles is considered for several geometrical arrangements. On this basis it is found that a binding energy of about 0.5 eV can be explained for trapped electrons in condensed alkanes. Although long range polarization interactions are unimportant, the electron interaction with the bond microdipoles of a net nonpolar molecule appears to be the key to understanding electron binding in alkane matrices.

Electron‐electron double resonance study of trapped electrons in γ‐irradiated 2‐methyltetrahydrofuran glass: Magnetic energy transfer between two different spin systems

Electron‐electron double resonance (ELDOR) of trapped electrons and radicals in γ‐irradiated 2‐methyltetrahydrofuran (MTHF) glass at 77°K was investigated. Magnetic energy pumped into the radical spin system is transferred to the trapped electron spin system to partially saturate it. The cross saturation mechanism is consistent with dipolar cross relaxation in which a radical spin flips down and an electron spin flips up. Analysis of the rate of spin relaxation shows that the reciprocal ELDOR reduction is linear with pumping microwave power with an intercept which gives the ratio of the cross‐relaxation time to the electron spin‐lattice relaxation time. The experimental data are found to fit this relationship. This ratio of relaxation times is of the order of 0.5 while the relaxation times themselves are in the 10−4‐sec range. The observation of cross relaxation in this system supports the concept that the trapped electron and radical are spatially correlated in γ‐irradiated MTHF.

Electron‐electron double resonance study of trapped electrons in 10M NaOH alkaline ice glass

Electron‐electron double resonance (ELDOR) has been used to test the validity of the noninteracting spin‐packet model for inhomogeneously broadened electron paramagnetic resonance (EPR) lines as applied to trapped electrons in 10M NaOH ice. Spectral simulation of field‐swept ELDOR spectra based on the spin‐packet model qualitatively, but not quantitatively, accounts for the observed spectra. The quantitative failure of the spin‐packet model is interpreted in terms of spin diffusion within the EPR line. Structure in frequency‐swept ELDOR spectra, which is not predicted by the spin‐packet model, has been observed and interpreted as ∼ 5.7 G hyperfine coupling with eight matrix protons. This supports a tetrahedral model of oriented water dipoles for the immediate environment of the trapped electron in alkaline ice.

A semi-continuum model for the solvated electron in methanol

Abstract The semi-continuum model for solvated electrons has been applied to methanol at 300°K. The configurational stability of the ground state was established and various physical properties of the solvated electron have been calculated and compared with experiment.

Electron–electron double resonance study of magnetic energy transfer between trapped electrons and radicals in organic glasses: Relation between dipolar cross relaxation times and dipolar interaction distances

Electron–electron double resonance (ELDOR) has been used to measure cross‐relaxation times between trapped electrons and trapped radicals produced by γ irradiation of 2‐methyltetrahydrofuran and 3‐methylhexane organic glasses. The cross‐relaxation times are measured as a function of temperature, radiation dose, and the frequency difference Δf of the microwave frequencies used. The cross‐relaxation times are nearly temperature independent and depend on Δf2 at doses where the spin concentrations approach uniformity; these features indicate the dominance of single step over multistep cross‐relaxation processes. Equations have been derived to relate the dipolar cross‐relaxation distance to the measured cross‐relaxation times, and it is suggested that the cross‐relaxation line shape is Lorentzian in magnetically dilute systems. Typical electron–radical correlation distances in these organic glasses are 10 A.