Thomas L. Allen

Bond Energies and the Interactions between Next‐Nearest Neighbors. I. Saturated Hydrocarbons, Diamond, Sulfanes, S8, and Organic Sulfur Compounds

Interaction energies of atoms which are next‐nearest neighbors have been determined from thermodynamic data for a number of carbon and sulfur molecules. When these interactions are taken into account, bond energies are found to be constant to a high degree of precision.Additional factors which have been considered include thermal and zero‐point energies, interactions of more distant neighbors, trigonal interactions, and ring strain.Simple equations for the prediction of unknown heats of formation are developed.

A possible role for triplet H2CN+ isomers in the formation of HCN and HNC in interstellar clouds

The structures and energies of the lowest triplet states of four isomers of H2CN+ have been determined by self‐consistent field and configuration interaction calculations. When both hydrogen atoms are attached to the nitrogen atom, H2NC+, the molecule has its lowest triplet state energy, which is 97.2 kcal mol−1 above the energy of the linear singlet ground state. The structure has C2v symmetry, with an HCH bond angle of 116.8°, and bond lengths of 1.009 A (H–N) and 1.268 A (N–C). Other isomers investigated include the H2CN+ isomer at 104.7, the cis‐HCNH+ isomer at 105.3, and the trans‐HCNH+ isomer at 113.6 kcal mol−1. The H2CN+ isomer has an unusual ’’carbonium nitrene’’ structure, with a C–N bond length of 1.398 A. It is suggested that the triplet H2NC+ isomer may play a role in determining the relative yields of HCN and HNC from the reaction of C+ and NH3. Specifically, a triplet path is postulated in which C+ and NH3 yield the triplet H2NC+ isomer, which then yields the singlet H2NC+ isomer by phospho...

Low-lying triplet states of diphosphene, HP=PH, and diphosphinylidene, H2P=P

Abstract Self-consistent-field and configuration-interaction studies have been carried out on several isomeric forms of the H 2 P 2 molecule in their closed-shell, n-π * triplet, and π-π * triplet states. Properties determined for each state include the relative energy, molecular geometry, dipole moment, and vibrational frequencies. Some unusual triplet states with highly distorted structures were found.

Absorption Spectra of I2 and I4 in CCl4 Solution

The absorption of light by solutions of iodine in carbon tetrachloride has been investigated from 250 mμ to 600 mμ. Deviations from Beers law occur in the region below 420 mμ. In this region the apparent extinction coefficient of the iodine is a linear function of its concentration. This can be accounted for on the basis that a weak complex of formula I4 exists in the solution in equilibrium with the diatomic molecules: 2I2=I4. The true extinction coefficient of I2 and the product of the formation constant and the extinction coefficient of I4 have been determined as a function of wavelength in this region.

Bond Energies of Transition Metal Halides

Bond energies of transition metal halides of the type MXn have been calculated from existing thermodynamic data. It has been found that the Pauling equation for the bond energies of polar bonds, in conjunction with Eleys method of calculating metal‐metal bond energies, is applicable to these molecules.

Least squares solution of the Schrödinger equation by a Monte Carlo method

Abstract The importance sampling method is applied to the least squares solution of the Schrodinger equation, using the spherical gaussian orbital to select points. Application to the helium atom gives good results with relatively few points.

Photochemistry of the gaseous hydrogen peroxide-carbon monoxide system III. Calculated energetics for possible HO2CO complexes

Abstract At 298 K, HO 2 radicals formed by secondary reactions in the photochemistry of the H 2 O 2 CO system do not react with CO, whereas OH radicals formed in the primary process do. To explain the non-reactivity of HO 2 , we made Hartree-Fock calculations of the energies needed to form three probable HO 2 -CO intermediate radical complexes: I , HOOĊO; II, III . The values of ΔE for the reaction HO 2 + CO → R and ΔH f o for R obtained at 298 K are as follows: From the high-temperature rate data, we conclude that the first stage of the reaction is the formation of complex I with ΔE the same or almost the same as the activation energy for the reaction to yield products CO 2 and OH, and that every collision of the reactants with sufficient energy yields the complex.

Bond Energies and the Interactions between Next‐Nearest Neighbors. II. Theoretical Calculations of Next‐Nearest‐Neighbor Interaction Energies in Saturated Hydrocarbons

Next‐nearest‐neighbor interactions in saturated hydrocarbons have been considered from a number of different points of view, including van der Waals radii, previous theoretical calculations of various types, nonbonded potential‐energy functions, magic‐formula calculations, and evidence from bond‐dissociation energies. Most methods indicate that the interactions are repulsions of several kcal/mole each. Two sets of potential functions give results in fairly good agreement with thermodynamic data. In each set the C···C function rises most steeply with decreasing distance and the H···H function least, a condition related to the thermodynamic data and the geometric mean used to obtain the H···C function. Magic‐formula calculations with invariant SCF orbitals lead to additivity of bond energies. Calculations on alkyl‐hydrogen bond‐dissociation energies indicate that methyl, ethyl, s‐propyl, and t‐butyl radicals have about the same reorganization energy, the decrease in bond dissociation energy on methyl substi...

Erratum to “Photochemistry of the gaseous hydrogen peroxide-carbon monoxide system. III. Calculated energetics for possible HO2CO complexes” [J. Photochem. Photobiol. A: Chem. 85 (1995) 201–205]

Abstract At 298 K, HO2 radicals formed by secondary reactions in the photochemistry of the H2O2CO system do not react with CO, whereas OH radicals formed in the primary process do. To explain the non-reactivity of HO2, we made Hartree-Fock calculations of the energies needed to form three probable HO2CO intermediate radical complexes: The values of ΔE for the reaction HO2+CO→R and δHf° for R obtained at 298 K are as follows: R I II (sym) II (anti) III (sym) III (anti) δE ( kJ ) 89 6 9 −280 −259 δH f ° ( kJ mol −1 ) −22 −105 −102 −391 −370 From the high-temperature rate data, we conclude that the first stage of the reaction is the formation of complex I with δE the same or almost the same as the activation energy for the reaction to yield products CO2 and OH, and that every collision of the reactants with sufficient energy yields the complex.