Overtone-initiated chemistry of atmospheric hydroperoxides Shizuka Hsieh, Chemistry Department, Smith College Northampton, MA 01063 Hydroperoxides absorbing visible sunlight become highly vibrationally excited. With enough energy in these excited molecules, the weak O-O bonds dissociate, forming hydroxyl (OH) radicals. Because OH radicals are important atmospheric oxidizing agents, we studied this process for gas-phase ethyl hydroperoxide excited with red light. OH*
O O CH2CH3
H
O O CH2CH3
H
CH3CH2O + OH
hνOH probe
trans H 3C
CH 2 O
gauche
O CH 2
H 3C
O O H
H
2
hνLIF
Absorption spectrum
1
0
15800
16200
16600
15800
16200
16600
4
Population
The experimental absorption spectrum (top left) and calculations (bottom left) show contributions from two ethyl hydroperoxide conformers. The trans conformer dominates at room temperature and is ~300 cm-1 lower in energy. Dissociation produces OH fragments with rotational distributions (right) that match statistical predictions (lines). Our experimental O-O bond dissociation energy (< 44 kcal mol-1) revises current literature values.
σ (10-24 cm2 molecule-1) σ (10-24 cm2 molecule-1)
OH
OH fragment rotational quantum states
0.1
2
0
0.0
Wavenumbers
(cm-1)
1
2
3
4
5
K
6
7
8
9
