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solutionexam - 5.68J/10.652J Spring 2003 Exam Question 3...

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± 5.68J/10.652J Spring 2003 Exam Question 3 with Solution The literature values for the Arrhenius parameters for OH + C(CH 3 ) 4 H 2 O+ (CH 3 ) 3 CCH 2 (Rxn 1) A= 10 9 liter/mole-second E a =20 kJ/mole You are suspicious of these round numbers, and want to check them experimentally. You decide to use HOOH as the precursor to generate the OH radicals by laser flash photolysis. You can get 4 mJ/pulse of 248 nm into the 1 cm 3 reaction volume in your cell, 20 2 the laser pulse duration is 50 ns, and σ 248 ( HOOH ) = 1 . 6 1 0 cm . You will probe the x OH by laser induced fluorescence, using optics which collect the light from the 1 cm 3 reaction volume in the center of your gas cell. The apparatus’s fluorescence collection/detection efficiency is 1%, so at best the peak Signal Counts ² # of OH formed ³ signal will be: = (0.01) * pulse ´ pulse µ where only the OH formed in the 1 cm 3 volume viewed by the detector contribute to the signal. Note that the percent uncertainty in your determination of the decay time constant τ will be about the same as the percent uncertainty in your signal measured at t = t photolysis + τ . You are worried that the competing reaction OH + HOOH H 2 O+ HO 2 (Rxn 2) with literature rate parameters A= 10 8 liter/mole-second E a =8 kJ/mole may cause difficulties; to minimize them you would like to run under conditions where

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solutionexam - 5.68J/10.652J Spring 2003 Exam Question 3...

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