Vapor deposition has been used to create glassy materials with extraordinary thermodynamic and kinetic stability and high density. For glasses prepared from indomethacin or 1,3-bis-(1-naphthyl)-5-(2-naphthyl)benzene, stability is optimized when deposition occurs on substrates at a temperature of 50 K below the conventional glass transition temperature. We attribute the substantial improvement in thermodynamic and kinetic properties to enhanced mobility within a few nanometers of the glass surface during deposition. This technique provides an efficient means of producing glassy materials that are low on the energy landscape and could affect technologies such as amorphous pharmaceuticals.

Research on parenting practices has revealed parental monitoring to be relevant to the safety of children (Peterson et al. 1993), the development of childhood antisocial behavior and substance use (Dishion, Li, Spracklen, Brown, and Haas, this volume), and academic achievement (Crouter et al. 1990). Parental monitoring, however, is not often the explicit target of even parent-focused prevention strategies. In this chapter, therefore, the authors focus exclusively on the construct of parental monitoring with respect to definition and developmental issues. In addition, measurement strategies and specific issues related to targeting monitoring in preventive intervention trials are discussed.

We present a direct measurement of self-diffusion of a single-component glass-forming liquid at the glass transition temperature. Forward recoil spectrometry is used to measure the concentration profiles of deuterio and protio 1,3-bis-(1-naphthyl)-5-(2-naphthyl)benzene (TNB) following annealing-induced diffusion in a vapor-deposited bilayer. These experiments extend the range of measured diffusion coefficients in TNB by 6 orders of magnitude. The results indicate a decoupling of translational diffusion coefficients from viscosity or rotation. At T(g), D(T) is 400 times larger than expected from the Stokes-Einstein equation.

A combination of experiment and theory provides insight into the structure and rearrangements of various C3H2 isomers. Photolysis of [13C]diazopropynes 6a−c under matrix isolation conditions affords C3H2 isomers containing a single 13C-label. With the aid of computed vibrational frequencies and intensities (CCSD(T)/cc-pVTZ), the seven 13C-isotopomers of triplet propynylidene 1a,b, singlet propadienylidene 2a−c, and singlet cyclopropenylidene 3a,b are readily distinguished by IR spectroscopy. Monitoring the distribution of the 13C-label during photolysis at either λ = 313 ± 10 nm or λ > 444 nm reveals the involvement of two photochemical automerization processes. At λ = 313 ± 10 nm, triplet propynylidene and singlet cyclopropenylidene photoequilibrate. The interconversion does not occur by a simple ring closure/ring opening mechanism, as hydrogen migration accompanies the interconversion. At λ > 444 nm, H2CC13C:  (2b) and H2C13CC:  (2c) rapidly equilibrate. Various lines of evidence suggest that the equilibration occurs through a cyclopropyne transition state. Computational results confirm that the planar isomer of singlet cyclopropyne (4a, C 2 v ) is the transition state for the interconversion of 2b and 2c. Unexpectedly, the calculations predict that the isomer of this compound containing a tetrahedral carbon atom (4b, C 2 v ) lies ca. 7 kcal/mol higher in energy than the planar form.

We calculate the first hyperpolarizability (β) of several thiazole and thiophene analogues of donoracceptor stilbene compounds using the ZINDO (sum-over-states) formalism. Because of the inherent dipolar nature of thiazole, in which C2 is electron-poor and C5 is electron-rich, the relative orientation of the thiazole subunit in the dipolar chromophore dramatically affects the nonlinear optical properties. In the "mismatched" case, the dipole of the thiazole ring opposes the molecular dipole created by the donor-acceptor substituents, while in the "matched" case, the dipole of the thiazole ring reinforces the molecular dipole. The hyperpolarizability of the "mismatched" monothiazole 2 (β µ ) 68 × 10 -30 cm 5 esu -1 ) exceeds that of stilbene 1 (β µ ) 34 × 10 -30 cm 5 esu -1 ) but is smaller than that of monothiophene 4 (β µ ) 90 × 10 -30 cm 5 esu -1 ). By contrast, the hyperpolarizability of the "matched" monothiazole 3 (β µ ) 177 × 10 -30 cm 5 esu -1 ) exceeds not only that of the "mismatched" monothiazole 2, but also that of monothiophene 4. Substituting thiazole for both aryl rings of stilbene produces very large hyperpolarizabilities in the "matched-matched" case (e.g., bis-thiazole 24, β µ ) 254 × 10 -30 cm 5 esu -1 ). The nonlinear optical response of heterocyclic analogues of donor-acceptor stilbene derivatives is discussed in terms of the difference in aromatic delocalization energy between phenyl, thiophene, and thiazole, the electronic nature of the heteroaromatic rings, and conformational factors.

Five isomers of the carbon-rich molecule C5H2 are investigated computationally, using methods based on the coupled-cluster approximation. All of these structures are related to isomers of C3H2 via substitution of hydrogen by ethynyl or attachment of a C2 fragment to a carbene center. The two most stable forms of C5H2 are linear triplet pentadiynylidene (4) and singlet ethynylcyclopropenylidene (6). Both of these isomers have been observed in the laboratory, as has a thirdthe cumulene carbene pentatetraenylidene (5)which is predicted to lie about 15 kcal/mol above the linear triplet. Two other isomers are also studied:  ethynylpropadienylidene (7) and 3-(didehydrovinylidene)cyclopropene (8). Both are found to lie less than 25 kcal/mol above the most stable form of C5H2 and to possess rather large dipole moments. Predictions for the harmonic vibrational frequencies of 12C and mono-13C isotopomers, infrared intensities, and rotational constants are also presented. These should assist efforts to identify these molecules in the laboratory and in the interstellar medium.

The understanding of mechanisms controlling zinc absorption and metabolism at the molecular level has advanced recently. Kinetics of zinc transport have been investigated for many years, but only recently have genes coding for proteins thought to be involved in the transport process been cloned.

The geometries and force fields of phenylcarbene (PC) and cycloheptatrienylidene (CHT) in their singlet and triplet electronic states as well as of cycloheptatetraene (CHTE) and bicyclo[4.1.0]heptatriene (BCT) and the transition states for the formation and decay of the latter were evaluated by various methods. Relative single point energies were calculated at the CCSD(T)/cc-pVDZ//BLYP/6-31G* level. Finally, the effects of extending the basis set to triple-ζ quality were estimated by (R)MP2 calculations and carried over proportionally to CCSD(T). These calculations show that CHTE which has a strongly distorted allenic structure is the most stable species on that part of the C(CH)6 surface which was examined in the present study, followed by planar 3PC. The strained BCT is found to be nearly degenerate in energy with 1PC, but the high activation energy for its formation from 1PC together with the low activation energy for ring-opening to CHTE suggests that this species cannot persist under the experimental conditions employed for production of CHTE. In analogy to the case of cyclopentadienylidene, CHT exists in the form of a closed shell singlet (1A1) and two related pairs of open shell singlet and triplet states (1,3A2 and 1,3B1) which correspond to the Jahn−Teller distorted structures of the cycloheptatrienyl radical. The relative energies and the nature of the different CHT stationary points depend on the method of calculation, but it appears that the decrease in electron repulsion lowers the 1A2 state slightly below the 1A1 state so that the open shell species serves as a planar transition state for enantiomerization of CHTE with an estimated activation energy of ∼20 kcal/mol. The two triplets are very close in energy with the higher lying being either a transition state or a shallow minimum. The 1B1 state is an excited state of the open-shell singlet. The calculated IR spectra of the three most stable isomers were compared to those published previously by Chapman et al. whereby the assignment of the photoproduct of UV photolysis of phenyldiazomethane to CHTE was confirmed. A full study of the force fields of PC and CHTE is under way.