1. light CH 4 + xs Br 2  CH 3 Br + HBr  CH 2 Br 2 + HBr  CHBr 3 + HBr  CBr 4 +HBr Traditional statement of overall methane (CH 4 ) + excess(xs) bromine (Br 2 ) gas phase reaction xs=> excess Br 2 is present h  1) CH 4 + Br 2  CH 4-x Br x + xHBr x=1,2,3 or 4 2) A slightly more detailed statement Product distribution depends on details of reaction conditions

2. Light source t=0.0 s CH 4 Br 2 0 0.01 t=0.01 trace CH 3 Br +HBr t= 1.0 CH 3 Br +HBr trace CH 2 Br 2 + more HBr 1.00 CHBr 3 t=50 trace CBr 4 50 s 0.01  50s all in dark Evacuated reaction bulb filled with CH 4 + Br 2 (xs) 25 0 CH 3 Br & CH 2 B r 2 graphical views of CH 4 + Br 2 reaction Quartz window ~Experimental set up Molecular detector

3. CH 4 CH 3 Br CH 2 Br 2 CHBr 3 CBr 4 Light on Dark ------  Time  concentratio n HBr Time evolution of reaction species concentrations for CH 4 + Br 2

4. Observed Behavior Patterns Summarized: 1) reaction will only go at >250 o C in dark or with input of ultraviolet (uv) light. 2) uv wavelength required which is near that for dissociation wavelength for X 2. 3) in excess X 2, a single photon (h ) event causes thousands of halogenations. (=> photo yield >>>>1, e.g. 1000-5000 halogenated methane molecules/1 photon of h.) 4) O 2 causes halogenation reaction to slow/stop. 5) reactivity rate : F 2 > Cl 2 > Br 2 > I 2.

5. http://www.youtube.com/watch?v=XAWWf86TJ0c http://www.youtube.com/watch?v=K6c9qfa1xiM Sort of Animation of free radical mechanism Demonstration of radical reaction with alkane + Br 2