Journal Details

1. Investigation of the Absorption Cross-Section of Phenyl Radical and Its Kinetics With Methanol in the Gas Phase Using Cavity Ring-Down Spectroscopy and Theoretical Methodologies.

K. Mondal, R. Kaipara and B. Rajakumar. J. Phys. Chem, 2019, 123(45), 9682-9692.

This article was selected as a 'Featured Content' in "ACS Aerosol and Atmospheric Chemistry Collection" for the year 2019-'20. Cavity ring-down spectroscopy (CRDS) was used to measure the absorption cross section of phenyl radicals (C6H5•) at 504.8 nm (2B1 ← 2A1 transition) in the nitrogen atmosphere at 40 Torr total pressure and 298 K using nitrosobenzene (C6H5NO) as the radical precursor. At 504.8 nm, the absorption cross section was measured to be σphenyl504.8 nm = (5.7 ± 1.4) × 10–19 cm2 molecule–1. The absorption cross section was independent of the total pressure range (40–200 Torr) over which it was studied with a precursor concentration of (4–5) × 1013 molecules cm–3. In addition to this, the absolute rate coefficients for the reaction of phenyl radicals with methanol were measured over the temperature range of 263–298 K and at 40 Torr pressure with N2 using CRDS. The temperature-dependent rate coefficient for the title reaction over the studied temperature range was obtained to be k263–298 Kexperiment (T) = (1.38 ± 0.60) × 10–11 exp [−(1764 ± 321)/T] cm3 molecule–1 s–1 with a rate coefficient of k(T) = (3.50 ± 0.32) × 10–14 cm3 molecule–1 s–1 at 298 K. The effect of pressure and laser fluence was found to be negligible within the experimental uncertainties in the studied range. In addition, to complement our experimental findings, the T-dependent rate coefficients for the title reaction were investigated using computational methods. The B3LYP/6-311 + G(d,p) level of theory was used in combination with canonical variational transition-state theory with small-curvature tunneling to calculate the rate coefficients. The T-dependent rate coefficient in the range of 200–400 K was obtained as k200–400 Ktheory (T) = 2.43 × 10–13 exp[−(478.38/T)] cm3 molecule–1 s–1 with a room-temperature (298 K) rate coefficient of 4.67 × 10–14 cm3 molecule–1 s–1.

Figure depicting the schematic representation of the in-built CRDS experimental set-up used in our laboratory of atmospheric chemistry. [PMT- Photo Multiplier Tube; MFC- Mass Flow Controllers; DAQ- Data Acquisition Card] The data regarding absorption cross section of phenyl radical and its pressure dependence have been included into the prestigious MPI Absorption Cross Section Database. Our data in MPI Cross Section Database