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Photodissociation of CH2I2 and subsequent electron transfer in solution.
Ken-Ichi Saitow1, Yukito Naitoh, Keisuke Tominaga
1The Graduate University for Advanced Studies, Myodaiji, Okazaki 444-8585, Japan. saitow@hiroshima-u.ac.jp
Chemistry, an Asian Journal
|April 3, 2008
Summary
Photoinduced reactions of diiodomethane (CH2I2) involve rapid radical formation and recombination, followed by slower charge-transfer complex and ion pair generation. Solvent influences aggregation and reaction kinetics, with acetonitrile showing saturation effects.
Area of Science:
- Photochemistry
- Chemical Kinetics
- Spectroscopy
Background:
- Diiodomethane (CH2I2) undergoes photoinduced reactions.
- Understanding these reactions is crucial for photochemistry and reaction dynamics.
Purpose of the Study:
- To investigate the photoinduced reaction pathways of diiodomethane (CH2I2).
- To elucidate the kinetics and mechanisms of transient species formation using time-resolved spectroscopy.
Main Methods:
- Subpicosecond-nanosecond transient absorption spectroscopy.
- Excitation at 268 nm in acetonitrile and hexane.
- Analysis of time-resolved spectra and reaction kinetics.
Main Results:
- Direct dissociation of CH2I2 forms CH2I radicals, which undergo geminate recombination.
- A concentration-dependent slow rise indicates charge-transfer (CT) complex formation (CH2I2(δ+)I(δ-)) and subsequent ion pair (CH2I2(+)I(-)) generation.
- Iodine species (I3-) are formed on the nanosecond timescale.
- Solvent effects on aggregation and CT complex formation were observed, with acetonitrile showing saturation.
Conclusions:
- The study elucidates the complex reaction mechanism of photoexcited diiodomethane.
- Concentration-dependent dynamics are attributed to CT complex formation in aggregates.
- Solvent properties influence solute aggregation and reaction pathways, affecting the upper limit of CT complex formation.
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