Functional Relationships between Kinetic, Flow, and Geometrical Parameters in a High-Temperature Chemical Microreactor.

Computational fluid dynamics (CFD) simulations and isothermal approximation were applied for the interpretation of experimental measurements of the C10H7Br pyrolysis efficiency in the high-temperature microreactor and of the pressure drop in the flow tube of the reactor. Applying isothermal approximation allows the derivation of analytical relationships between the kinetic, gas flow, and geometrical parameters of the microreactor, which, along with CFD simulations, accurately predict the experimental observations. On the basis of the obtained analytical relationships, a clear strategy for measuring rate coefficients of (pseudo) first-order bimolecular and unimolecular reactions using the microreactor was proposed. The pressure- and temperature-dependent rate coefficients for the C10H7Br pyrolysis calculated using variable reaction coordinate transition state theory were invoked to interpret the experimental data on the pyrolysis efficiency.

O2(b1Σg+) Removal by H2, CO, N2O, CH4, and C2H4 in the 300-800 K Temperature Range.

Rate constants for the removal of O2 b1Σg+ by collisions with species relevant to combustion, H2, CO, N2O, CH4 and C2H4 have been measured in the temperature range 297-800 K. O2(b1Σg+) was produced from ground-state molecular oxygen by photoexcitation pulses from a tunable dye laser, and the deactivation kinetics were followed by observing the temporal behavior of the b1Σg+-X3Σg- fluorescence. The removal rate constants for H2, CO, N2O, CH4, and C2H4 could be represented by the modified Arrhenius expressions kH2 = (1.44 ± 0.02) × 10-16 T1.5 exp[(0 ± 10)/ T], kCO = (6.9 ± 0.4) × 10-24 T3 exp[(939 ± 33)/ T], kN2O = (2.63 ± 0.14) × 10-18 T1.5 exp[(590 ± 26)/ T], kCH4 = (3.5 ± 0.2) × 10-17 T1.5 exp[(-220 ± 24)/ T], and kC2H4 = (2.34 ± 0.10) × 10-20 T2.5 exp[(680 ± 16)/ T] cm3 molecule-1 s-1, respectively. All of the rate constants measured at room temperature were found to be in good agreement with previously reported values, whereas the values at elevated temperatures up to 800 K were systematically measured for the first time.

O2(b1Σg+) Quenching by O2, CO2, H2O, and N2 at Temperatures of 300-800 K.

Rate constants for the removal of O2(b1Σg+) by collisions with O2, N2, CO2, and H2O have been determined over the temperature range from 297 to 800 K. O2(b1Σg+) was excited by pulses from a tunable dye laser, and the deactivation kinetics were followed by observing the temporal behavior of the b1Σg+-X3Σg- fluorescence. The removal rate constants for CO2, N2, and H2O were not strongly dependent on temperature and could be represented by the expressions kCO2 = (1.18 ± 0.05) × 10-17 × T1.5 × exp[Formula: see text], kN2 = (8 ± 0.3) × 10-20 × T1.5 × exp[Formula: see text], and kH2O = (1.27 ± 0.08) × 10-16 × T1.5 × exp[Formula: see text] cm3 molecule-1 s-1. Rate constants for O2(b1Σg+) removal by O2(X), being orders of magnitude lower, demonstrated a sharp increase with temperature, represented by the fitted expression kO2 = (7.4 ± 0.8) × 10-17 × T0.5 × exp[Formula: see text] cm3 molecule-1 s-1. All of the rate constants measured at room temperature were found to be in good agreement with previously reported values.

Luminescence of the (O2(a(1)Δ(g)))2 collisional complex in the temperature range of 90-315 K: Experiment and theory.

Experimental and theoretical studies of collision induced emission of singlet oxygen molecules O2(a(1)Δg) in the visible range have been performed. The rate constants, half-widths, and position of peaks for the emission bands of the (O2(a(1)Δg))2 collisional complex centered around 634 nm (2) and 703 nm (3) have been measured in the temperature range of 90-315 K using a flow-tube apparatus that utilized a gas-liquid chemical singlet oxygen generator. The absolute values of the spontaneous emission rate constants k2 and k3 are found to be similar, with the k3/k2 ratio monotonically decreasing from 1.1 at 300 K to 0.96 at 90 K. k2 slowly decreases with decreasing temperature but a sharp increase in its values is measured below 100 K. The experimental results were rationalized in terms of ab initio calculations of the ground and excited potential energy and transition dipole moment surfaces of singlet electronic states of the (O2)2 dimole, which were utilized to compute rate constants k2 and k3 within a statistical model. The best theoretical results reproduced experimental rate constants with the accuracy of under 40% and correctly described the observed temperature dependence. The main contribution to emission process (2), which does not involve vibrational excitation of O2 molecules at the ground electronic level, comes from the spin- and symmetry-allowed 1(1)Ag←(1)B3u transition in the rectangular H configuration of the dimole. Alternatively, emission process (3), in which one of the monomers becomes vibrationally excited in the ground electronic state, is found to be predominantly due to the vibronically allowed 1(1)Ag←2(1)Ag transition induced by the asymmetric O-O stretch vibration in the collisional complex. The strong vibronic coupling between nearly degenerate excited singlet states of the dimole makes the intensities of vibronically and symmetry-allowed transitions comparable and hence the rate constants k2 and k3 close to one another.