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The rate constant for the overall reaction OH + 1-butanol → products was determined in the temperature range 900 to 1200 K from measurements of OH concentration time histories in reflected shock wave experiments of tert-butyl hydroperoxide (TBHP) as a fast source of OH radicals with 1-butanol in excess. Narrow-linewidth laser absorption was employed for the quantitative OH concentration measurement. A detailed kinetic mechanism was constructed that includes updated rate constants for 1-butanol and TBHP kinetics that influence the near-first-order OH concentration decay under the present experimental conditions, and this mechanism was used to facilitate the rate constant determination. The current work improves upon previous experimental studies of the title rate constant by utilizing a rigorously generated kinetic model to describe secondary reactions. Additionally, the current work extends the temperature range of experimental data in the literature for the title reaction under combustion-relevant conditions, presenting the first measurements from 900 to 1000 K. Over the entire temperature range studied, the overall rate constant can be expressed in Arrhenius form as 3.24 × 10(-10) exp(-2505/T [K]) cm(3) molecule(-1) s(-1). The influence of secondary reactions on the overall OH decay rate is discussed, and a detailed uncertainty analysis is performed yielding an overall uncertainty in the measured rate constant of ±20% at 1197 K and ±23% at 925 K. The results are compared with previous experimental and theoretical studies on the rate constant for the title reaction and reasonable agreement is found when the earlier experimental data were reinterpreted.

Rate constants for the overall reactions of OH with n-pentane, n-heptane, and n-nonane were measured in shock tube experiments behind reflected shock waves. Narrow-linewidth laser absorption by OH at 306.7 nm was used in pseudo first-order experiments with temperatures between 869 to 1364 K. tert-Butyl hydroperoxide (TBHP) was used as the OH precursor. Experiments were also performed to study the kinetics of the TBHP decomposition and resulting product chemistry, and an accurate mechanism describing OH precursor chemistry effects was developed to model OH concentration time-history in the n-alkane + OH experiments. The experimental results for the n-alkane + OH rate constant measurements can be expressed as rate constants in Arrhenius form as k n-pentane + OH = 2.10 × 10-10 exp(-2038/T[K]) (869–1364 K), k n-heptane + OH = 2.43 × 10-10 exp(-1804/T[K]) (869–1364 K), k n-nonane + OH = 3.17 × 10-10 exp(-1801/T[K]) (884–1352 K), each in units of cm3 molecule-1 s-1. The present rate constants measured for OH with n-pentane and n-heptane show agreement within 20% with recent work by Sivaramakrishnan and Michael [J. Phys. Chem. A, 113 (2009) 5047]. The measurements of the rate constant for n-nonane + OH presented here represent the first in the literature to depict the temperature dependence of the rate constant above 800 K. The measurements of each n-alkane + OH rate constant studied were compared with two models in the literature used to estimate the rate constants of n-alkane + OH reactions. The Structure-Activity Relationship of Kwok and Atkinson [Atmos. Environ., 29 (1995) 1685] shows the best agreement with the current data for all three n-alkanes over the entire temperature range studied, demonstrating that this model is capable of predicting the overall rate constants for reactions of OH with n-pentane, n-heptane, and n-nonane for temperatures up to 1364 K.

Gold nanoparticles can be used as an exogenous contrast agent for biomedical photoacoustic (PA) imaging. The generation of PA signals in monodispersed gold nanosphere suspensions (diameters 20–150 nm) from pulsed-laser excitation (5 ns pulse width, wavelength 532 nm) was investigated experimentally and compared to signals measured in solutions of a homogeneous molecular absorber. The PA signal amplitude was found to increase linearly with excitation fluence for the homogeneous absorber and the nanospheres up to 80 nm in diameter. By contrast, the signal amplitude was found to increase quadratically with respect to fluence for larger nanospheres. In the linear regime, the PA signal amplitude in gold nanosphere suspensions was found to be on average 26% higher than that in the homogeneous absorber with identical absorption coefficient, which were measured using an integrating sphere. Furthermore, in suspensions with identical absorption coefficient, no dependence of the PA signal amplitude on nanosphere diameter was found in the linear regime, entailing that suspensions with identical extinction coefficient display a decreasing trend in PA signal amplitude with increasing nanosphere diameter due to increasing contribution of scattering. This study presents experimental evidence of some of the physical phenomena governing the photoacoustic signal generation in gold nanosphere suspensions, which may inform on approaches to molecular biomedical PA imaging.

This work presents the first direct experimental study of the rate constant for the reaction of OH with iso-butanol (2-methyl-1-propanol) at temperatures from 907 to 1147 K at near-atmospheric pressures. OH time-histories were measured behind reflected shock waves using a narrow-linewidth laser absorption method during reactions of dilute mixtures of tert-butylhydroperoxide (as a fast source of OH) with iso-butanol in excess. The title reaction's overall rate constant (OH + iso-butanol →(k(overall)) all products) minus the rate constant for the β-radical-producing channel (OH + iso-butanol →(k(β)) 1-hydroxy-2-methyl-prop-2-yl radical + H(2)O) was determined from the pseudo-first-order rate of OH decay. A two-parameter Arrhenius fit of the experimentally determined rate constant in the current temperature range yields the expression (k(overall) - k(β)) = 1.84 × 10(-10) exp(-2350/T[K]) cm(3) molecule(-1) s(-1). A recommendation for the overall rate constant, including k(β), is made, and comparisons of the results to rate constant recommendations from the literature are discussed.

Deep-tissue 3-dimensional monitoring of RFA lesion generation in real time was demonstrated for the first time in this work. The results suggest the potential of optoacoustic monitoring for providing critical feedback on lesion position and size during radiofrequency catheter ablation, improving safety and efficacy of these treatments.

Silica-coated gold nanoparticles are commonly employed in biomedical photoacoustic (PA) imaging applications. We investigate theoretically and experimentally the PA signal generation by silica-coated gold nanospheres in water. Our theoretical model considers thermoelastic expansion in the long-pulse illumination regime, and the PA signals are determined based on a semianalytical solution to the thermal diffusion equations and a finite-difference in time domain (FDTD) solution to the thermoelastic equations. Both the influence of interfacial thermal (Kapitza) resistance at the gold-water boundary and the influence of the silica coating on PA signal generation were investigated. Our results indicate that for the nanosecond pulses commonly employed in PA imaging, Kapitza resistance has a negligible effect on photoacoustic signal generation. Moreover, our model shows that the presence of a silica coating causes a reduction in the PA signal amplitude, with the level of signal reduction increasing with thicker silica coating.Our theoretical predictions are qualitatively consistent with our experimental results, where suspensions of in-house-synthesized and commercially available silica-coated gold nanosphere suspensions were excited with nanosecond-pulsed laser illumination at 532 nm. The PA signal amplitudes from silica-coated nanospheres were lower than the signal amplitudes for uncoated gold nanospheres of the same core gold diameter. The amount of reduction of the experimentally PA signal amplitude due to the silica coating was found to increase with thicker silica coating, in agreement with our theoretical predictions.

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