机理?
Br2—hν→Br·+Br·
CH3CH3+Br·—→CH3CH2·+HBr
CH3CH2·+Br2—→CH3CH2Br+Br·
CH3CH2·+Br·—→CH3CH2Br
Br·+Br·—→Br2
CH3CH2·+CH3CH2·—→CH3CH2CH2CH3