Virginia Griffing

The Chemical Effects of Ultrasonics

A study of the effects of ultrasonics on the inversion of sucrose was made and negative results were obtained. In the light of these results one can make the following conclusions.Chemical reactions attributed to ultrasonics can be classified according to three mechanisms. (1) Reactions due to cavitation never occur without the formation of bubbles. All of these reactions take place in the gas phase, are primarily thermal and are due to the heat developed during adiabatic compression. Thus, only reactants with an appreciable vapor pressure are affected. (2) Many reactions in the liquid phase are of secondary origin due to reactions with dissolved products of the primary reaction in the gas phase. Luminescense is also a secondary effect. (3) Some reactions are due to the uniform temperature elevation caused by absorption of acoustic energy of very high intensity in a short path length.

Studies of the Interaction between Stable Molecules and Atoms. II. Interaction between Two He Atoms

The repulsive energy of two helium atoms has been calculated using molecular orbital theory. The equations of Roothaan were used to break down the energy into integrals involving atomic orbitals. The necessary integrals are tabulated in the literature for a wide range of parameter which enabled the potential energy curve to be calculated from R=0.6 to 7.0 a0. The Slater (1s) orbital with effective nuclear charge Z=27/16 was used. The potential curve is lower at all distances from those of other investigators in the range where Van der Waals forces give attraction although the curves agree at closer distances. Ionization energies have been calculated over these distances and extrapolated to infinity to give a value which is much better than that calculated with the same orbital by ordinary means. The addition of 2pσ character to the molecular orbitals by constructing hybrid orbitals of the type N {(1s)+λ(2pσ)} and the determination of λ by a SCF calculation according to the scheme of Roothaan, gives an att...

LCAO‐MO SCF Study of B2

An LCAO molecular orbital study of B2 was made for three distances of the internuclear parameter. SCF molecular orbitals were obtained for the 3Σg— state, which is the reported ground state of the molecule. Total molecular energies of other low‐lying states were calculated using the 3Σg— SCF molecular orbitals. These results indicate that the 5Σu— state is the ground state of B2; however, the 3Σg— and 3Πu states lie only about 1.5 ev above the 5Σu— state and may become lower in a more refined calculation.A Mulliken electronic population analysis was applied to B2. For comparative purposes a summary of overlap and atomic populations of Li2, C2, N2, and O2 is included.

Luminescence Produced as a Result of Intense Ultrasonic Waves

The luminescence produced by intense ultrasonic waves has been investigated in a number of water solutions and organic liquids in the frequency range 0.66—2.0 mc/sec. Together with direct visual tests, quantitative measurements have been performed for which a photometric method has been developed. The results show that luminescence, when it does occur, is always present with cavitation and starts at the same sound intensity as cavitation. A quantitative relationship is established between intensity of luminescence and chemical yield induced by ultrasonics. From this it is concluded that, at least in some of these cases, the phenomenon is chemiluminescence. None of the organic liquids tested showed any luminescence except for nitrobenzene in which the luminescence was very weak in the frequency range and under the physical conditions examined. It is not possible at present to conclude whether this weak luminescence is due to some chemical reaction occurring in it or to a different process. An apparent frequency dependence for the intensity of luminescence was observed; however, it is shown that the threshold of cavitation is the frequency‐dependent phenomenon.

Studies of the Interaction between Stable Molecules and Atoms. IV. The Energy of the Linear H4 Complex

Roothaans LCAO—SCF treatment has been applied to the linear symmetrical H4 complex in an attempt to test this method for calculating the energies of activated complexes. Calculations have been made for internuclear distances of 1.4, 1.6, 2.0, and 2.2 a.u. The SCF method gives a lower value for the energy of 1.4 a.u. than was obtained by a simple molecular orbital method without configuration interaction, but gives a higher value than the best configuration interaction treatment. The values of the energies that were obtained are —55.48, —55.99, —56.50, and —56.54 ev at distances of 1.4, 1.6, 2.0, 2.2 a.u., respectively. The changes in the wave functions as one adiabatically changes the internuclear distance are of particular interest. Although the results cannot be directly compared with experiment, reasonable values for the energy are obtained indicating that the molecular orbital SCF method with a limited amount of configuration interaction is a promising method for treating closed‐shell molecules and i...

INTERACTION ENERGY OF AN ALKALI METAL WITH A RARE GAS

A molecular orbital self‐consistent field calculation is made for closed shell ions, LiHe+ and LiHe— as function of internuclear distance. The eigenfunctions obtained from these calculations were used to calculate the potential energy curves for the neutral Li–He. This system has some interesting properties. For example, these calculations suggest the probable quenching of certain excited states of an alkali metal when in close interaction with a rare‐gas atom. All of the curves obtained are repulsive except for the LiHe+ curve which has a shallow minimum and follows an expected 1/r4 attractive potential. Fair values are obtained for the ionization energies of the Li and He atoms and the electron affinity of Li. These calculations indicate that open‐shell systems with few electrons can be treated by making the simpler SCF calculation on a closely related closed‐shell system and using the resulting eigenfunctions to calculate the energy of the closed shell system.

Studies of the Interaction between Stable Molecules and Atoms. I. A Molecular Orbital Theory of the Activation Energy between Molecules and Atoms

The molecular orbital method of calculation is applied to the interaction between closed‐shell species; the results discussed in this paper and presented in the following papers of this series indicate that this method will yield quantitative results for energies of a system as function of internuclear parameters if one is interested in the differences in energy for two different geometric ground state configurations of the system. The molecular orbitals are used as a basis of constructing correlation diagrams for predicting mechanisms and calculating activation energies for chemical reactions. The orbitals of the reactants and products are correlated with the orbitals of a state defined as the ambivalent complex. The low‐lying excited states of the interacting molecules seem to be of importance in determining the activation energy of a chemical reaction. Considerable qualitative insight into the activation process is gained by this method; the relative values of the activation energies for the interactio...

Quantum Mechanical Study of the Hydrogen Bimolecular Exchange Reaction

A theoretical calculation of the potential‐energy curves of several linear four‐atom hydrogen complexes has been made in order to study the interaction governing the kinetics of the bimolecular exchange reaction. In particular, an attempt was made to determine for what distance of approach the two diatomic molecules make a transition into the four‐atom complex. Hence, the linear H4 complex H—r—H—R—H—r—H was chosen for study as function of r and R. The partial potential energy surface constructed in this manner indicates that two hydrogen molecules approaching on a line experience an increase in interatomic separation with the inner two atoms forming a hydrogen molecule at small separations while the outer two atoms are repelled outward from the center of the system. The minimum occurs for r=R=1.8 and gives an activation energy of 65 kcal for the bimolecular exchange reaction, if one assumes a linear transition state.An additional calculation was performed on a linear chain of six hydrogen atoms with inter...

Studies of the Interaction between Stable Molecules and Atoms. V. Molecular Orbital Approach to the H+H2 Reaction

In an attempt to find a relatively simple way of calculating activation energies for chemical reactions, Roothaans LCAO‐SCF method has been applied to the linear H3 complex. Since Roothaans method has been developed for closed shells, a self‐consistent field treatment has been done on the linear H3— complex. According to Roothaan, the energy of the H3 should be equal to a first approximation to the energy of the H3— minus the energy required to remove one electron. Calculations have been made at distances ranging from 1.4 to 2.5 atomic units and for various values of the screening constant. Correlation diagrams for the reaction H+H2 have been constructed and the activation energy calculated. The method gives considerable insight into charge distribution but is unsatisfactory for calculating good energy values. The results are compared with experiment and with values calculated by the MO‐configuration interaction method which yields a value of 8.76 kcal/mole.

The Size and Vibration Frequency of the Excited Benzene Molecule

It is shown that the change in size and vibration frequency of a polyatomic molecule upon electronic excitation can be calculated if the excitation energy is known as function of the distance. This is applied to benzene, for which this function is calculated both with the Heitler‐London‐Slater‐Pauling method and the molecular orbital method. Upon comparison with experiment, it is found that both methods give the right sign and order of magnitude for the change in size, but the wrong sign for the change in frequency.