F. A. Long

Study of the Mass Spectra of the Lower Aliphatic Alcohols

Mass spectra and appearance potentials have been determined for methanol, ethanol, and propanol. These data are used in semiempirical application of the statistical theory of mass spectra. The theory facilitates assignment of plausible mechanisms for the production of the various ion fragments. It is possible to obtain computed spectra in agreement with experimental data using an internally consistent set of structural parameters.

Mass Spectra of Some Simple Esters and Their Interpretation by Quasi‐Equilibrium Theory

Mass spectra and appearance potential data are reported for normal and isotopically labeled methyl formate, methyl acetate, and ethyl formate, and reaction mechanisms are proposed for the production of the spectra. The data are analyzed from the standpoint of the quasi‐equilibrium theory of Eyring and co‐workers. For the data from 70‐volt ionizing electrons, frequency factors can be adjusted so that the calculated patterns agree well with the experimental data. These frequency factors seem qualitatively satisfactory although there are some difficulties with the values for some of the rearrangements and hydrogen abstraction processes. However the theory is clearly inadequate at lower ionizing voltages. The probable explanation is that the electronic states are in narrow bands which do not overlap, so that at low voltages a portion of the ionic fragments are produced by direction dissociation, without the redistribution of energy which is required by the quasi‐equilibrium theory.

Diffusion of Acetone into Polyvinyl Acetate above and below the Second‐Order Transition

The sorption kinetics for the system polyvinyl acetate‐acetone have been investigated both above and below 30°C, the second‐order transition temperature for the pure polymer. At 30, 40, and 50°C, the diffusion obeys Ficks law with a concentration‐dependent diffusion coefficient. With increasing acetone concentration the value of the diffusion coefficient increases strongly, and the energy of activation for diffusion decreases. At each temperature below 30°C, diffusion is Fickian only for sorption and desorption experiments where the solvent concentration is above a certain critical value. It was found, by comparison with the results of volume‐temperature measurements on the system polyvinyl acetate‐acetonyl acetone, that the temperature corresponding to a given critical concentration is the second‐order transition temperature for this polymer‐solvent mixture. Evidently, the changes which occur at the second‐order transition have a pronounced influence on the diffusion process.

INFLUENCE OF COMPETITIVE DECOMPOSITION PROCESSES ON IONIZATION EFFICIENCY CURVES FROM ELECTRON IMPACT

The energy dependence of ionization efficiency by electron impact for polyatomic molecules is influenced by the entrance of decomposition processes. The observed yield of parent ion drops sharply at the energy onset of a high‐yield decomposition process. Ionization efficiency curves for products from other decomposition processes are similarly effected. These effects are particularly apparent for decomposition processes with energy thresholds some volts above the parent ion appearance potential, and this is illustrated by data for the ionization efficiencies from the molecules NH3, C2H4, and C2F4. Perturbation from such competitive processes can result in erroneously high measured appearance potentials for the product ions.

Interdiffusion of Polyvinyl Acetate with a Series of Solvents

The Lamm scale method has been used to follow the interdiffusion of polyvinyl acetate with ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, and triacetin at 30°C, and with acetone at 20°, 30°, and 40°C. For all these systems the mutual diffusion coefficient attains a maximum value at intermediate polymer concentrations. At a given concentration and temperature the D(c) values are largest with acetone and much the smallest with triacetin, although the relative variation in D(c) over the concentration range is actually largest with the latter. The general variation of D(c) with concentration can be plausibly interpreted in terms of the mass flow‐intrinsic diffusion concept introduced by Hartley. For the system acetone—polyvinyl acetate the calculated energy of activation for the diffusion is nearly constant at 1 kcal in the concentration range 0 to 40 grams polymer per 100 cc of solution but then rises rapidly to 10 kcal at 90 grams polymer per 100 cc.

Statistical Theory of Mass Spectra: Difficulties in Interpretation of Spectra of the Lower Alkanes

Mass spectra of a group of normal alkanes, C4 through C8, have been studied as a function of ionizing voltage. Appearance potentials have also been measured for most of the ions. At all voltages the yields of the ion fragments produced by loss of hydrogen atoms and by loss of methyl radicals are surprisingly low relative to their appearance potentials. Since for the lower ionizing voltages it can safely be assumed that there are no significant contributions to the patterns from secondary decompositions, these low yields must indicate a low intrinsic probability for the primary processes by which these ions are formed. For the typical case of n‐pentane, the experimental data have been analyzed from the standpoint of the statistical theory of mass spectra and it is found that frequency factors in the ratio of 1:104:108 must be proposed to account for the yields from the hydrogen atom:methyl radical:ethyl radical extraction processes at low ionizing voltages. The implications of this wide range of frequency ...

VARIATION OF APPEARANCE POTENTIALS OF ALKANE FRAGMENT IONS WITH THE REPELLER VOLTAGE OF THE MASS SPECTROMETER ION SOURCE

The differences in the mass spectrometric appearance potentials for parent molecule ions and the ion fragments which are formed from the parent by hydrogen abstraction have been measured for propane, n‐butane, and n‐pentane as a function of the repeller voltage in the ion source. With pentane, the potential difference varies from close to zero for no repeller voltage to 1.1 volts for 0.5 volt repeller voltage or higher. There is a similar but smaller increase of 0.6 volt with n butane, while with propane the changes in appearance potentials are well within the experimental error. Of the various explanations considered, the most likely is that zero repeller voltage leads to relatively longer ion residence times in the source and that, as a result, some low‐probability de‐excitation processes have time to occur. This implies that appearance potentials which are obtained for this type of process with use of the usual repeller voltages can be considerably in excess of the minimum threshold energies.

EQUILIBRIUM IN THE DEUTERIUM EXCHANGE OF ACETYLENE AND WATER

The isotopic‐exchange equilibrium between acetylene gas and deuterated water vapor has been experimentally studied over a wide range of deuterium content in the temperature range from 5° to 85°. The equilibrium constant K7 for the gas‐phase reaction C2H2+D2O=C2D2+H2O is 0.473±0.008 at 25°. The thermodynamic parameters for the reaction are ΔH°=0.29 kcal/mole and ΔS°=—0.56 eu at 25°. The equilibrium constant for the disproportionation reaction C2H2+C2D2=2C2HD has also been measured and is found to have a constant value of 3.95±0.10 for the temperature range 5° to 85°. The exchange constant K7 has been calculated from the available spectroscopic data for the relevant acetylene and water species and the theoretical values agree with the experimental values to within 10%. The observed data for both the exchange and disproportionation reactions are consistent with those for similar systems.

Appropriate technology and social values : a critical appraisal

In 1978, an international conference on technology choice and social values in the developed and developing nations was held at the Wingspread Conference Center of theJohnson Foundation in Racine, Wisconsin. The conference, organized by the American Academy, the International Pugwash Council, and the U.S. Pugwash Committee, was supported by grants from the National Science Foundation, the Johnson Foundation, and the Exxon Corporation. A number of the papers preparedfor the symposium have been edited by Franklin A. Long (Cornell University) and Alexandra Oleson (American Academy of Arts and Sciences) for publication in a volume to be issued early in 1980 by the Ballinger Publishing Company. What follows is Mr. Longs introduction to the volume.

Government Dollars for University Research.

While government grants to universities for research and development have increased under the Reagan Administration, unprecedented portions of the monies have been devoted to Defense Department activities.