1. Matrix isolation and computational study of iso-difluorodibromomethane (F 2 CBr-Br): A route to molecular products in CF 2 Br 2 Photolysis Lisa George, Aimable Kalume, and Scott A. Reid, Department of Chemistry, Marquette University, Milwaukee, WI 53233; Patrick Z. El-Khoury and Alexander Tarnovsky, Department of Chemistry and center for Photochemical Sciences, Bowling Green State University, Bowling Green, OH 43403 Date: June 22, 2010

2. Introduction to CF 2 Br 2 Photolysis (The nature of the photodissociation process is discussed in light of previous and present results) Experimental Techniques & Computational Methods Infrared, UV/Vis, Computational results and discussion Outline of the Talk

3. CF 2 Br 2 (Halon 1202) Relevant to atmospheric chemistry, fire retardants, and potential for ozone depletion UV photodissociation of CF 2 Br 2 involving C-Br fission in an initial step, followed by a second C-Br fission as a result of IVR, leads to :CF 2 Isoenergetic dissociation channels 1) a radical channel yielding CF 2 Br + Br, and 2) a molecular elimination channel yielding :CF 2 + Br 2 Photochemistry of Halons

4. What are the products of CF 2 Br 2 photolysis? CF 2 Br 2 + hν CF 2 Br + Br CF 2 + Br 2 MAJOR MINOR 4% in CRDS expt. ~ 188 and 226 nm. Lin et al. J.Chem. Phys. 2000, 125, 143312

5. Previous Studies on the Photolysis of CF 2 Br 2 M.E Jacox, Chemical Physics Letters, 1978, 54, 176 CF 2 Br 2 :Ar = 1:270 (CF 2 Br radical C2F4 and C2F4Br2 )., Cameron and Bacskay, J.Phys.Chem. 2000, 104, 11212, reported iso-CF 2 Br 2 as TS Br + CF 2 Br  :CF 2 + Br 2 CASSCF/cc-pVDZ (Dalton programs)

6. 10 -6 mbar To DP Sample/ RG KBr window Cold Head 5 K hν Pulsed deposition Laser Photolysis Measure Anneal Experimental setup (FTIR,UV/Vis) (35K)

7. Inspiration for this study Goal of this study was to observe the iso-form of CF 2 Br 2 (F2CBr-Br) using Matrix isolation infrared and UV/Vis. Spectroscopy, supported by computation Recent observation and characterisation of iso-CF 2 I 2 led to this study iso-CF 2 I 2 spectrum

8. Photolysis of CF 2 Br 2 F 2 CBr 2 F 2 CBr-Br hν 240 and 266 nm

9. Infrared and UV/Vis Spectra As Deposited 240 nm Annealed at 35 K TDB3LYP/aug-cc-pVTZ 359nm (331nm f=0.27) 536nm (528nm f=0.005) B3LYP/aug-cc-pVTZ ν 1 1188,1203 (769) ν 7 1240, 1234 (295) ν 3 509, 493 (79)

10. Relaxed PES of iso-CF 2 Br 2 B3LYP/aug-cc-pVDZ Relaxed PES along the Br-Br stretching and C-Br-Br bending coordinates at the B3LYP/cc-pVXZ B3LYP/aug-cc-pVXZ MP2/cc-pVXZ MP2/aug-cc-pVXZ (X=D, T, Q) 2.5 Å 158 (140)

11. :CF2---Br2 complex Relaxed PES along the C-Br stretching and C-Br-Br bending coordinates B3LYP/aug-cc-pVDZ ……

12. B3LYP/aug-ccpVTZ//CCSD(T)/aug-cc-pVDZ + + Stationary points on the CF 2 Br 2 PES

13. IRC Plot B3LYP/aug-ccpVTZ

14. Reaction Sequence CF 2 Br 2 + h ϑ  CF 2 Br + Br (1) CF 2 Br + Br  iso-CF 2 Br 2 (2) iso-CF 2 Br 2  :CF 2 + Br 2 (3) CF 2 Br (+h ϑ )  :CF 2 + Br (4)

15. Summary Wavelength dependent mechanisms of the photochemical reactions of Difluorodibromomethane (CF 2 Br 2 ; Halon 1202) has been proposed Iso-CF 2 Br 2, a weakly bound isomer of CF 2 Br 2 isomer was observed in matrix infrared and UV/Visible spectra obtained following photodissociation of CF 2 Br 2 at either 240 nm or 266 nm Iso-CF 2 Br 2 is an intermediate in the Br + CF 2 Br  : CF 2 + Br 2 reaction confirmed by PES

16.  Professor Scott. A. Reid Aimable Kalume Dr. Victoria Ayles Lloyd Muzangwa National Science Foundation and Petroleum Research Fund Acknowledgments

17. Experimental Procedure CF 2 Br 2 is mixed with Ar, M:S ratio is 1: 5000 Gas mixture is co-deposited on a cold substrate KBr or CaF 2 at 5K and Probed by IR, UV/Vis. Spectroscopy Low Temp. He displex (ARS Displex DE-204S) Supersonic jet sampling, Pulse duration is 500 micro Sec., repetition rate of 5 Hz FTIR spectrometer (Mattson, Galaxy series) equipped with a DTGS detector ( 1 cm -1 resolution and 128 scans ), Agilent 8453 diode array spectrophotometer Photolysis Sources used 266 nm and 240 nm B3LYP/aug-cc-pVTZ, CCSD(T)/aug-cc-pVDZ (Single point)

18. Photolysis Condition 1)The cold window was irradiated with laser light at 266 nm, generated from the fourth harmonic of a pulsed Nd:YAG laser (Continuum Minilite) 2) 240 nm, generated from the frequency doubled output of a dye laser system (Lambda-Physik Scanmate 2E) operating on Coumarin 480 dye, pumped by the third harmonic (355 nm) of a Nd:YAG laser (Continuum NY-61). Typical irradiation times were 1.5 h at 240 nm (10 ns pulses, 1 mJ/pulse, 10 Hz), and 5 h at 266 nm (5 ns pulses, 2.3 mJ/pulse, 5 Hz). The gas-phase absorption cross-section of the parent at 210 K is around 30 times larger at 240 nm than at 266 nm.

19. CF 2 Br 2 :Ar matrix (240 nm, annealed, computation) B3LYP/aug-cc-pVTZ ν 1 1188,1203 (769) ν 7 1240, 1234 (295) ν 3 509, 493 (79) wavenumber (cm -1 )

20. Photolysis at 266 nm

21. CF 2 Br 2 annealing Parent annealed