Ab initio potential and dipole moment surfaces for water. II. Local-monomer calculations of the infrared spectra of water clusters

We employ recent flexible ab initio potential energy and dipole surfaces [Y. Wang, X. Huang, B. C. Shepler, B. J. Braams, and J. M. Bowman, J. Chem. Phys. 134, 094509 (2011)] to the calculation of IR spectra of the intramolecular modes of water clusters. We use a quantum approach that begins with a partitioned normal-mode analysis of perturbed monomers, and then obtains solutions of the corresponding Schro?dinger equations for the fully coupled intramolecular modes of each perturbed monomer. For water clusters, these modes are the two stretches and the bend. This approach is tested against benchmark calculations for the water dimer and trimer and then applied to the water clusters (H(2)O)(n) for n = 6-10 and n = 20. Comparisons of the spectra are made with previous ab initio harmonic and empirical potential calculations and available experiments.     

An ab initio spin-orbit-corrected potential energy surface and dynamics for the F + CH4 and F + CHD3 reactions

We report an analytical ab initio three degrees of freedom (3D) spin-orbit-correction surface for the entrance channel of the F + methane reaction obtained by fitting the differences between the spin-orbit (SO) and non-relativistic electronic ground state energies computed at the MRCI+Q/aug-cc-pVTZ level of theory. The 3D model surface is given in terms of the distance, R(C-F), and relative orientation, Euler angles ? and θ, of the reactants treating CH(4) as a rigid rotor. The full-dimensional (12D) "hybrid" SO-corrected potential energy surface (PES) is obtained from the 3D SO-correction surface and a 12D non-SO PES. The SO interaction has a significant effect in the entrance-channel van der Waals region, whereas the effect on the energy at the early saddle point is only ～5% of that at the reactant asymptote; thus, the SO correction increases the barrier height by ～122 cm(-1). The 12D quasiclassical trajectory calculations for the F + CH(4) and F + CHD(3) reactions show that the SO effects decrease the cross sections by a factor of 2-4 at low collision energies and the effects are less significant as the collision energy increases. The inclusion of the SO correction in the PES does not change the product state distributions.     

Living radical photopolymerization induced grafting on thiol–ene based substrates

The formation of reactive substrates with iniferter‐mediated living radical photopolymerization is a powerful technique for surface modification, which can readily be used to facilitate the incorporation of a variety of surface functionalities. In this research, the photopolymerization kinetics of novel bulk thiol–ene systems have been compared with those of typical acrylate and methacrylate systems when polymerized in the presence of the photoiniferter p‐xylene bis(N,N‐diethyl dithiocarbamate) (XDT). In the presence of XDT, the thiol–ene systems photopolymerize more quickly than the traditional acrylate and methacrylate systems by one to two orders of magnitude. Fourier transform infrared spectroscopy has been used to monitor the photografting kinetics of various monomers on dithiocarbamate‐functionalized surfaces. Furthermore, this technique has been used to evaluate surface‐initiation kinetics and to emphasize the influence of bulk substrate properties on grafting kinetics. Finally, photopatterning has been demonstrated on a dithiocarbamate‐incorporated thiol–ene substrate with conventional photolithographic techniques. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2134–2144, 2005     

Picosecond transient photoreflectance measurements of ion-implanted GaAs

We have used picosecond transient reflectance techniques to measure the near-surface characteristics of ion-implanted GaAs. These non-destructive laser-based diagnostic techniques allow measurement of the modification of near-surface properties at relatively low implant fluences. Photothermal phenomena dominate these results and yield important information concerning the extent of implant-induced materials modification.     

A model study of the laser-induced stabilization of a collision complex

The possibility of stabilizing a collision complex by stimulated emmission with coherent radiation is explored for a model. three-atom system. The lifetimes of several resonance states of this system were obtained previously and are used in a simple two-level model to describe the interaction of radiation with a resonance state and a true bound state. For the case where the energy difference between the two levels is time independent, simple, analytical expressions are used to obtain the time-dependent transition probability. Numerical solutions are obtained for the more realistic case where this energy difference is time dependent. For both cases, a substantial transition probability for stabilization is calculated for moderate laser intensities (e.g. 8.1 kW/cm² for an assumed dipole matrix element of 0.01 D).     

Electron excitation in atoms and molecules by neutron-nucleus scattering

The quantum theory of electron stimulated desorption developed in two preceding papers is presented in a WKB like form and is applied to the desorption of hydrogen and oxygen from tungsten. Retunnelling processes are taken into account and manifest themselves in an imaginary part in the potential of the desorbing particles. This imaginary part together with a non zero width of the wavepacket leads to quantum effects in the motion of the desorbing particles modifying the corresponding classical results of the reduction factor and of the energy conservation. The modifications turn out to be quite large for hydrogen as well as for oxygen increasing the reduction factor by several orders of magnitude. The isotope effect also is changed appreciable. The parameters of the model are determined from corresponding experimental data such as vibrational levels of the adsorbates, the energy distribution of the desorbing particles and the reduction factor.     

A novel SRN1 substitution: the reaction between the anion of 2-nitropropane and 3-bromo-1-nitrocyclohex-1-ene

X-Ray crystallography has been used to determine the unusual cyclopropyl structure for the product of the S_RNl reaction between the anion of 2-nitropropane and 3-bromo-1-nitrocyclohex-1-ene.     

Radical-nucleophilic substitution (SRN1) reactions: preparation and reactions of aliphatic α-Nitro-azides

α-Nitro-azides were prepared by two routes involving intermediate radical-anions, and undergo substitution by an S_RN1 mechanism with azides, sulphinates, and thiolates to give loss of nitrite, and with nitronates to give loss of azide.     

Bounds for the expectation of the kth root of a random variable

Exact bounds for the mean value of a fractional moment, such as the sample standard deviation, are considered. These bounds are compared with those found by summation techniques applied to computer extended series. An expansion involving an arbitrary parameter is introduced, and now best bounds are found by optimization. There are applications to bounds for a certain class of quadrature problem.