TY - JOUR
T1 - Bimolecular reaction of CH 3 + CO in solid p -H 2
T2 - Infrared absorption of acetyl radical (CH
3
CO) and CH
3
-CO complex
AU - Das, Prasanta
AU - Lee, Yuan-Pern
PY - 2014/1/1
Y1 - 2014/1/1
N2 -
We have recorded infrared spectra of acetyl radical (CH
3
CO) and CH
3
-CO complex in solid para-hydrogen (p-H
2
). Upon irradiation at 248 nm of CH
3
C(O)Cl/p-H
2
matrices, CH
3
CO was identified as the major product; characteristic intense IR absorption features at 2990.3 (ν
9
), 2989.1 (ν
1
), 2915.6 (ν
2
), 1880.5 (ν
3
), 1419.9 (ν
10
), 1323.2 (ν
5
), 836.6 (ν
7
), and 468.1 (ν
8
) cm
- 1
were observed. When CD
3
C(O)Cl was used, lines of CD
3
CO at 2246.2 (ν
9
), 2244.0 (ν
1
), 1866.1 (ν
3
), 1046.7 (ν
5
), 1029.7 (ν
4
), 1027.5 (ν
10
), 889.1 (ν
6
), and 723.8 (ν
7
) cm
- 1
appeared. Previous studies characterized only three vibrational modes of CH
3
CO and one mode of CD
3
CO in solid Ar. In contrast, upon photolysis of a CH
3
I/CO/p-H
2
matrix with light at 248 nm and subsequent annealing at 5.1 K before re-cooling to 3.2 K, the CH
3
-CO complex was observed with characteristic IR features at 3165.7, 3164.5, 2150.1, 1397.6, 1396.4, and 613.0 cm
- 1
. The assignments are based on photolytic behavior, observed deuterium isotopic shifts, and a comparison of observed vibrational wavenumbers and relative IR intensities with those predicted with quantum-chemical calculations. This work clearly indicates that CH
3
CO can be readily produced from photolysis of CH
3
C(O)Cl because of the diminished cage effect in solid p-H
2
but not from the reaction of CH
3
+ CO because of the reaction barrier. Even though CH
3
has nascent kinetic energy greater than 87 kJ mol
- 1
and internal energy ∼ 42 kJ mol
- 1
upon photodissociation of CH
3
I at 248 nm, its energy was rapidly quenched so that it was unable to overcome the barrier height of ∼ 27 kJ mol
- 1
for the formation of CH
3
CO from the CH
3
+ CO reaction; a barrierless channel for formation of a CH
3
-CO complex was observed instead. This rapid quenching poses a limitation in production of free radicals via bimolecular reactions in p-H
2
.
AB -
We have recorded infrared spectra of acetyl radical (CH
3
CO) and CH
3
-CO complex in solid para-hydrogen (p-H
2
). Upon irradiation at 248 nm of CH
3
C(O)Cl/p-H
2
matrices, CH
3
CO was identified as the major product; characteristic intense IR absorption features at 2990.3 (ν
9
), 2989.1 (ν
1
), 2915.6 (ν
2
), 1880.5 (ν
3
), 1419.9 (ν
10
), 1323.2 (ν
5
), 836.6 (ν
7
), and 468.1 (ν
8
) cm
- 1
were observed. When CD
3
C(O)Cl was used, lines of CD
3
CO at 2246.2 (ν
9
), 2244.0 (ν
1
), 1866.1 (ν
3
), 1046.7 (ν
5
), 1029.7 (ν
4
), 1027.5 (ν
10
), 889.1 (ν
6
), and 723.8 (ν
7
) cm
- 1
appeared. Previous studies characterized only three vibrational modes of CH
3
CO and one mode of CD
3
CO in solid Ar. In contrast, upon photolysis of a CH
3
I/CO/p-H
2
matrix with light at 248 nm and subsequent annealing at 5.1 K before re-cooling to 3.2 K, the CH
3
-CO complex was observed with characteristic IR features at 3165.7, 3164.5, 2150.1, 1397.6, 1396.4, and 613.0 cm
- 1
. The assignments are based on photolytic behavior, observed deuterium isotopic shifts, and a comparison of observed vibrational wavenumbers and relative IR intensities with those predicted with quantum-chemical calculations. This work clearly indicates that CH
3
CO can be readily produced from photolysis of CH
3
C(O)Cl because of the diminished cage effect in solid p-H
2
but not from the reaction of CH
3
+ CO because of the reaction barrier. Even though CH
3
has nascent kinetic energy greater than 87 kJ mol
- 1
and internal energy ∼ 42 kJ mol
- 1
upon photodissociation of CH
3
I at 248 nm, its energy was rapidly quenched so that it was unable to overcome the barrier height of ∼ 27 kJ mol
- 1
for the formation of CH
3
CO from the CH
3
+ CO reaction; a barrierless channel for formation of a CH
3
-CO complex was observed instead. This rapid quenching poses a limitation in production of free radicals via bimolecular reactions in p-H
2
.
UR - http://www.scopus.com/inward/record.url?scp=84903710689&partnerID=8YFLogxK
U2 - 10.1063/1.4883519
DO - 10.1063/1.4883519
M3 - Article
C2 - 24985634
AN - SCOPUS:84903710689
VL - 140
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
SN - 0021-9606
IS - 24
M1 - 244303
ER -