No abstract

A molecular beam technique for studying the decomposition of vapor-phase glycine on solid surfaces has been developed. The decomposition probability of glycine on the surfaces of polycrystalline molybdenum oxide and glass was measured as a function of the surface temperature. Decomposition products were quantitatively analyzed with a mass spectrometer in the temperature range of 420–800 K. The probability of decomposition of glycine per one collision with molybdenum oxide was found to be almost unity at a high surface temperature (∼800 K), while that with glass was less than 0.15 in the observed temperature range. The values of activation energy E and the pre-exponential factor S Z 2/Z 1 for the decomposition are determined. A new model based on the transition state theory to evaluate the values of the pre-exponential factor is proposed.

The frontier-electron theory based on extended Hückel calculation is applied to a ring cluster molecule to model a hygroscopic reaction in phosphate glass. It is shown that H+ rather than OH- plays a more important role in the reaction.

A novel experimental method for the spectroscopy of nonbeam low density gas has been developed to probe the interaction between molecules and solid surfaces. Translational and rotational temperatures of the molecules scattered from solid surfaces are measured as a function of surface temperature. The results are critically dependent on the kind of surfaces (glass, graphite, silver, mica, and molybdenum oxide). A new model describing the mechanism of energy transfer from solid surfaces to molecules is proposed. A good agreement between observation and calculation is obtained.

Reaction pathways and energetics for the dimerization and trimerization reactions of 2-bromo-3-methoxythiophene (2Br-3Met) molecules are investigated using hybrid density functional theory (DFT) calculations to obtain insight into the oligomerization reaction observed in the spontaneous combustion of pure liquid 2Br-3Met. The calculations show that the carbon−bromine bond in a 2Br-3Met molecule elongates easily, and the trans addition of this C−Br bond to a double bond in the neighboring 2Br-3Met molecule occurs easily at room temperature, reflecting the evaluated activation energy of ΔH a = 12.46 kcal/mol (enthalpy) or ΔG a = 35.68 kcal/ mol (Gibbs free energy, 298.150 K and 1 atm). The formation process of trimers is calculated in a similar way. A model for the explanation of spontaneous combustion is proposed; large oligomers of the 2Br-3Met molecule are produced spontaneously following the initial formation of dimers or trimers. UV−vis spectra and vibration spectra are obtained for related molecular species, which show reasonable agreement with the experimental results.