Bromine Monoxide Radical Reaction with Propyl-Peroxy and Isopropyl-Peroxy Radicals: Thermokinetic Insights from Cavity Ring-Down Spectroscopy

The experimental rate coefficients for the reaction of bromine monoxide (BrO) with propyl peroxy (PrO₂) and isopropyl peroxy (<i>i</i>-PrO₂) radicals were determined using cavity ring-down spectroscopy in the temperature ranges of 263-338 and 253-383 K, respectively. The rate coefficient for the BrO + PrO₂ was measured to be (1.43 ± 0.14) × 10^-12 cm³ molecule^-1 s^-1 and for the BrO + <i>i</i>-PrO₂ as (0.76 ± 0.01) × 10^-12 cm³ molecule^-1 s^-1 at 298 K and 95 Torr. The temperature has an inverse effect on the rate coefficients in the studied range, given by <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mi>k</mml:mi><mml:mrow><mml:mo>(</mml:mo><mml:mi>T</mml:mi><mml:mo>)</mml:mo></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mi>B</mml:mi><mml:mi>r</mml:mi><mml:mi>O</mml:mi></mml:mrow><mml:mo>+</mml:mo><mml:msub><mml:mrow><mml:mi>P</mml:mi><mml:mi>r</mml:mi><mml:mi>O</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow><mml:mrow><mml:mn>263</mml:mn><mml:mo>-</mml:mo><mml:mn>338</mml:mn><mml:mi>K</mml:mi></mml:mrow></mml:msubsup></mml:math> = <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>(</mml:mo><mml:mn>2.55</mml:mn><mml:mo>±</mml:mo><mml:mn>0.92</mml:mn><mml:mo>)</mml:mo></mml:math> × <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mn>10</mml:mn><mml:mrow><mml:mo>-</mml:mo><mml:mn>14</mml:mn></mml:mrow></mml:msup><mml:mi>exp</mml:mi><mml:mrow><mml:mo>[</mml:mo><mml:mrow><mml:mo>(</mml:mo><mml:mn>1228.6</mml:mn><mml:mo>±</mml:mo><mml:mn>244.0</mml:mn><mml:mo>)</mml:mo></mml:mrow><mml:mo>/</mml:mo><mml:mi>T</mml:mi><mml:mo>]</mml:mo></mml:mrow></mml:math> cm³ molecule^-1 s^-1 and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mi>k</mml:mi><mml:mrow><mml:mo>(</mml:mo><mml:mi>T</mml:mi><mml:mo>)</mml:mo></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:mi>B</mml:mi><mml:mi>r</mml:mi><mml:mi>O</mml:mi></mml:mrow><mml:mo>+</mml:mo><mml:mi>i</mml:mi><mml:mo>-</mml:mo><mml:msub><mml:mrow><mml:mi>P</mml:mi><mml:mi>r</mml:mi><mml:mi>O</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow><mml:mrow><mml:mn>253</mml:mn><mml:mo>-</mml:mo><mml:mn>383</mml:mn><mml:mi>K</mml:mi></mml:mrow></mml:msubsup></mml:math> = <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>(</mml:mo><mml:mn>1.58</mml:mn><mml:mo>±</mml:mo><mml:mn>0.48</mml:mn><mml:mo>)</mml:mo></mml:math> × <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mn>10</mml:mn><mml:mrow><mml:mo>-</mml:mo><mml:mn>14</mml:mn></mml:mrow></mml:msup><mml:mi>exp</mml:mi><mml:mrow><mml:mo>[</mml:mo><mml:mrow><mml:mo>(</mml:mo><mml:mn>1093.7</mml:mn><mml:mo>±</mml:mo><mml:mn>147.0</mml:mn><mml:mo>)</mml:mo></mml:mrow><mml:mo>/</mml:mo><mml:mi>T</mml:mi><mml:mo>]</mml:mo></mml:mrow></mml:math> cm³ molecule^-1 s^-1. The rate coefficient was negligibly affected by the pressure variation from 95 to 220 Torr. The multireference theoretical calculations using the CASPT2-F12/AVDZ//M062-X/AVDZ level of theory for the H-abstraction reaction channel were used to determine the electronic energies of all species involved in the reactions. The reaction rate coefficient was calculated by using canonical variational transition (CVT) state theory with small curvature tunneling corrections, yielding results that are in close agreement with the experimentally measured values. At 298 K, the calculated rate coefficient for BrO + PrO₂ was 1.49 × 10^-12 cm³ molecule^-1 s^-1, while for the BrO + <i>i</i>-PrO₂, it was calculated to be 0.83 × 10^-12 cm³ molecule^-1 s^-1, which is close to the experimental result within the error limit. The rate coefficient for the recombination reaction of the radicals BrO + PrO₂ and BrO + <i>i</i>-PrO₂ was calculated to be 0.87 × 10^-12 and 0.52 × 10^-12 cm³ molecule^-1 s^-1 at 298 K and 95 Torr, using MESMER simulation at CCSD(T)/complete basis set (1/X³; AVTZ/AVDZ)//M06-2X/AVDZ theory.