Secondary ion mass spectrometry has been used to characterize translational motion in vapor-deposited glasses of indomethacin (IMC) and α,α,β-tris-naphthylbenzene (TNB). Vapor deposition onto substrates at ∼0.99 T(g) produced ordinary glasses that evolve according to fickian diffusion during annealing. The resulting self-diffusion coefficients for the supercooled liquids are in good agreement with previous reports. Deposition onto substrates at 0.85 T(g) produced highly stable glasses that transform with a propagating front mechanism. In contrast to previous reports, the liquid produced by this transformation has the same translational mobility as the ordinary supercooled liquid; we associate this result with lower impurity levels in the current samples. The front velocities for both TNB and IMC stable glasses are very similar functions of the translational self-diffusion coefficients of the supercooled liquids, consistent with view that the growth front velocity is controlled by mobility in the liquid adjacent to the stable glass.

Physical vapor deposition of organic molecules can produce glasses with high kinetic stability and low enthalpy. Previous experiments utilizing wide-angle x-ray scattering (WAXS) have shown that, relative to the ordinary glasses prepared by cooling the supercooled liquid, such glasses exhibit excess scattering characteristic of anisotropic packing. We have used vapor deposition to prepare glasses of four isomers of tris-naphthylbenzene (TNB), and measured both the WAXS patterns and the kinetic stability. While vapor-deposited glasses of all four TNB isomers exhibit high and nearly uniform kinetic stability, the level of excess scattering varies significantly. In addition, for α,α,β-TNB, glasses of essentially identical kinetic stability can have excess scattering levels that vary by a factor of two. These results indicate that anisotropic packing is not the source of kinetic stability in vapor-deposited glasses but rather a secondary feature that depends upon the chemical structure of the glass-forming molecules. We also show that the time required for these stable vapor-deposited glasses to transform into the supercooled liquid greatly exceeds the structural relaxation time τ(α) of the liquid and scales approximately as τ(α) (0.6). The kinetic stability of the vapor-deposited TNB glasses matches that expected for ordinary glasses that have been aged for 10(2) to 10(7) years.

A s a liquid is cooled, the time required for molecular rearrangements lengthens. If a liquid can be cooled below the

The reaction of the chemical warfare agent VX with hydroxide and hydroperoxide has been studied using a combination of correlated molecular orbital and density functional theory. It is found that the alkaline hydrolysis leads to a mixture of neurotoxic and non‐toxic products while hydroperoxidolysis leads to exclusive formation of non‐toxic products. Natural bond orbital (NBO) analysis is used to rationalize the observation that hydroxide will attack opposite the alkoxide ligand, while hydroperoxide will attack opposite the thiolate. The current results are in good agreement with previous experimental and computational work and serve to clarify the mechanism for destruction of this highly potent nerve agent. Copyright © 2008 John Wiley & Sons, Ltd.

Photolysis (λ > 543 nm) of 3-thienyldiazomethane (1), matrix isolated in Ar or N2 at 10 K, yields triplet 3-thienylcarbene (13) and α-thial-methylenecyclopropene (9). Carbene 13 was characterized by IR, UV/vis, and EPR spectroscopy. The conformational isomers of 3-thienylcarbene (s-E and s-Z) exhibit an unusually large difference in zero-field splitting parameters in the triplet EPR spectrum (|D/hc| = 0.508 cm−1, |E/hc| = 0.0554 cm−1; |D/hc| = 0.579 cm−1, |E/hc| = 0.0315 cm−1). Natural Bond Orbital (NBO) calculations reveal substantially differing spin densities in the 3-thienyl ring at the positions adjacent to the carbene center, which is one factor contributing to the large difference in D values. NBO calculations also reveal a stabilizing interaction between the sp orbital of the carbene carbon in the s-Z rotamer of 13 and the antibonding σ orbital between sulfur and the neighboring carbon—an interaction that is not observed in the s-E rotamer of 13. In contrast to the EPR spectra, the electronic absorption spectra of the rotamers of triplet 3-thienylcarbene (13) are indistinguishable under our experimental conditions. The carbene exhibits a weak electronic absorption in the visible spectrum (λmax = 467 nm) that is characteristic of triplet arylcarbenes. Although studies of 2-thienyldiazomethane (2), 3-furyldiazomethane (3), or 2-furyldiazomethane (4) provided further insight into the photochemical interconversions among C5H4S or C5H4O isomers, these studies did not lead to the spectroscopic detection of the corresponding triplet carbenes (2-thienylcarbene (11), 3-furylcarbene (23), or 2-furylcarbene (22), respectively).