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Reactions of iodine atoms, chlorine atoms and of chlorine oxides followed by Kinetic spectroscopy

University of British Columbia

The recombination of I atoms in mixtures of NO and inert gas was studied by flash photolysis. The mechanism proposed is: I + NO + M [sup → sub <-]INO + M 1. K₁,₋₁ = K₁,K₋₁ I + INO → I₂ + NO 2. K₂ 2INO - I₂ + 2NO 3. K₃ 2I + M → I₂ + M 4. K₄ A new system of the INO spectrum was observed from 310 to 251 nm with an extinction coefficient which increases towards shorter wavelengths from 107 to 1.57 x 10⁴ lmol⁻¹cm⁻¹. At low pressures of NO(P[sub NO]≤ 53 Pa or 0.4 torr), [INO] is in a steady state and reaction (1) is rate determining. At high pressures of NO (0.67 kPa or 5 torr < P[sub NO] < 106 kPa or 800 torr), [I] is in a steady state and reaction (3) dominates. The following rate constants and activation energies were measured: K₁ = 3.74 x 10⁹ l²mol⁻²s⁻¹; E [sub act(l)] = -3.4 kJmol⁻¹ (for M = Ar) K₂ ≥ 5 x 10⁹ lmol⁻¹s⁻¹ K₃ = 3.95 x 10⁷ lmol⁻¹s⁻¹; E [sub act(3)] = 13 kJmol⁻¹ K₄ = 4.72 x 10⁹ l²mol⁻²s⁻¹; E [sub act(4)] = -4.3 kJmol⁻¹ (for M = Ar) 107 lmol⁻¹≤ K₁, ₋₁ ≤ 2.1 x 10¹⁰ lmol⁻¹ 3.74 x 10² lmol⁻¹ ≥ K₋₁≥ 0.178 lmol⁻¹ Using a calculated value of ΔS₁ = -100 Jmol⁻¹K⁻¹ then 62 kJmol⁻¹ ≤ -ΔH₁ (I-NO bond strength) ≤ 81 kJmol⁻¹. C1OO is the precursor to the C1Oradical following photolysis of mixtures of Cl₂ and O₂. The mechanism proposed is: Cl + O₂ + M [sup → sub <-] ClOO + M 5. K₅,₋₅ = K₅/k₋₅ (for M = Ar) Cl + C1OO→ Cl₂ + O₂ 6. K₆ Cl + C1OO → 2C1O 7. K₇ The C1OO spectrum was observed in absorption with [C1OO] in equi1ibriurn with [Cl] and [O₂]. The following were measured: K₆/K₇ = 16 K₅,₋₅K₇ = 6.03 x 10⁹ l²mol⁻²s⁻¹ The decay of ClO was studied using C1O₂, C1₂O and (Cl₂ + O₂) as sources. The reaction is third order with ClO decaying to C1₂O₂. 2C1O + M [sup → sub <-] C1₂O₂ + M 8. K₈,₋₈= K₈/K₋₈ (M = Ar) A new spectrum attributed to C1₂O₂ is observed extending from 292 to 232 nm with the extinction coefficient increasing towards lower wavelengths from 360 to 2.61 x 10³ lmol⁻¹cm⁻¹. The equilibrium is established slowly giving: K₈ = 3.74 x 10⁹ l²mol⁻²s⁻¹ K₈,₋₈= 2.9 x 10⁹ lmol⁻¹ K₋₈ = 1.29 lmol⁻¹s⁻¹ Using ΔH₁ = -84 Jmol⁻¹K⁻¹ then ΔH₁ = -71.5 kJmol⁻¹. C1₂O₂ is proposed to decay by a chain mechanism involving Cl and C1OO.

Text

2010-01-26

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http://hdl.handle.net/2429/19145

Chemistry

University of British Columbia

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