Strain-induced changes to the electronic structure of nanoscale materials provide a promising avenue for expanding the optoelectronic functionality of semiconductor nanostructures in device applications. Here we use pump-probe microscopy with femtosecond temporal resolution and submicron spatial resolution to characterize charge-carrier recombination and transport dynamics in silicon nanowires (NWs) locally strained by bending deformation. The electron-hole recombination rate increases with strain for values above a threshold of ∼1% and, in highly strained (∼5%) regions of the NW, increases 6-fold. The changes in recombination rate are independent of NW diameter and reversible upon reduction of the applied strain, indicating the effect originates from alterations to the NW bulk electronic structure rather than introduction of defects. The results highlight the strong relationship between strain, electronic structure, and charge-carrier dynamics in low-dimensional semiconductor systems, and we anticipate the results will assist the development of strain-enabled optoelectronic devices with indirect-bandgap materials such as silicon.

The photolysis of benzene/ozone mixtures in an argon matrix at 12 K with UV light of λ ≥ 280 nm leads to the following products:  phenol, 2,4-cyclohexadienone, benzene oxide, and butadienylketene (hexa-1,3,5-trien-1-one). The identification of butadienylketene as a product is based on deuterium isotopic shifts and agreement with density functional vibrational frequency calculations. We find an average phenol/butadienylketene branching ratio of 4.3 during the course of photolysis. This is the first report in the literature of the observation of a ketene product from the reaction of oxygen atoms with benzene.

The rate coefficient has been measured under pseudo-first-order conditions for the Cl+CH3 association reaction at T=202, 250, and 298 K and P=0.3-2.0 Torr helium using the technique of discharge-flow mass spectrometry with low-energy (12-eV) electron-impact ionization and collision-free sampling. Cl and CH3 were generated rapidly and simultaneously by reaction of F with HCl and CH4, respectively. Fluorine atoms were produced by microwave discharge in an approximately 1% mixture of F2 in He. The decay of CH3 was monitored under pseudo-first-order conditions with the Cl-atom concentration in large excess over the CH3 concentration ([Cl]0/[CH3]0=9-67). Small corrections were made for both axial and radial diffusion and minor secondary chemistry. The rate coefficient was found to be in the falloff regime over the range of pressures studied. For example, at T=202 K, the rate coefficient increases from 8.4x10(-12) at P=0.30 Torr He to 1.8x10(-11) at P=2.00 Torr He, both in units of cm3 molecule-1 s-1. A combination of ab initio quantum chemistry, variational transition-state theory, and master-equation simulations was employed in developing a theoretical model for the temperature and pressure dependence of the rate coefficient. Reasonable empirical representations of energy transfer and of the effect of spin-orbit interactions yield a temperature- and pressure-dependent rate coefficient that is in excellent agreement with the present experimental results. The high-pressure limiting rate coefficient from the RRKM calculations is k2=6.0x10(-11) cm3 molecule-1 s-1, independent of temperature in the range from 200 to 300 K.

In the effort to compute molecular properties more accurately and at a lower cost in terms of computational time, density functional theory has emerged as an alternative to more expensive methods to include correlation corrections. In this paper the optimized geometries, harmonic frequencies, and electronic energies of ab initio calculations performed on borazine and the fluorinated derivatives of borazine at the B3LYP/6-31G** and MP2(FC)/6-31G** levels of theory are presented. We compare the results of the density functional method with second-order perturbation theory and, where possible, compare experimental observations with computed properties. A qualitative assessment of the aromaticity of borazine as a function of fluoro substitution is proposed. The calculations indicate, at both levels of theory, evidence for in-plane π bonding between fluorine and boron and fluorine and nitrogen in the fluorinated deriatives of borazine.

Rate constants for the gas-phase reactions of OH radical, NO 3 radical, and ozone with allyl alcohol (AAL) and allyl isocyanate (AIC) have been measured using relative rate methods at atmospheric pressure in purified air. The experimental Arrhenius expression obtained for the reaction of the OH radical with AAL is (1.68 ( 0.89) × 10 -12 × exp(1100/T) cm 3 molecule -1 s -1 , for T ) 282-315 K; the Arrhenius expression for the reaction of OH radical with AIC is (1.94 ( 1.04) × 10 -14 × exp(2207/T) cm 3 molecule -1 s -1 , for T ) 282-317 K, where the indicated errors are one least-squares standard deviation. All OH radical reaction rate constants have been measured relative to k(OH + R-pinene) and k(OH + 1,3,5-trimethylbenzene). The rate constant for the gas-phase reaction of OH radical with allyl alcohol-d 6 isotopomer (AAL-d 6 ) has been measured at T ) 298 K, and the value is 5.10 × 10 -11 cm 3 molecule -1 s -1 . The kinetic isotope effect is small, with k(AAL)/k(AAL-d 6 ) ) 1.32. Rate constants for the gas-phase reactions of NO 3 radical with AAL [relative to k(NO 3 +methacrolein)] and O 3 [relative to k(O 3 + β-pinene)] have been measured, and the values are 7.7 × 10 -15 cm 3 molecule -1 s -1 at T ) 298 K and 1.6 × 10 -17 cm 3 molecule -1 s -1 at T ) 296 K, respectively. Rate constants for the gas-phase reactions of NO 3 radical and O 3 with AIC have been measured, and the values are 9.4 × 10 -16 cm 3 molecule -1 s -1 at T ) 299 K and 5.54 × 10 -18 cm 3 molecule -1 s -1 at T ) 299 K, respectively. Multireference ab initio calculations at the MRMP2/6-311G(d,p) level have been carried out for reactions of OH radical with AAL and AIC. Results indicate that prereactive hydrogen bonded complexes form in the entrance channels for these reactions.