Patrick Z. El-Khoury, Alexander N. Tarnovsky, and Massimo Olivucci Structure of the Photochemical Reaction Pathway Populated via the Promotion of CF 2 I 2 into its First Excited State Department of Chemistry and Center for Photochemical Sciences Bowling Green State University International Symposium on Molecular Spectroscopy Mini-Symposium: Conical Intersections BGSU Department of Chemistry

X -1 X Y -1 Y El-Khoury, Tarnovsky, CPL 2007 El-Khoury, Kwok, Guan, Ma, Phillips, Tarnovsky, CPC 2009 El-Khoury, Olivucci, Tarnovsky, CPL 2008 El-Khoury, Schapiro, Ryazantsev, Tarnovsky, Olivucci, JPC A 2009, submitted Dissociation Escape Recombination Trapping Vibrational relaxation Cooling

CF 2 I 2 : Early Gas-Phase Work Excitation in the nm range exclusively causes direct two-body decay CF 2 I 2 *  CF 2 I· + I·( 2 P 3/2 ) Excitation at < 266 nm: a concerted decay CF 2 I 2 *  CF 2 + I· + I· Intermediate wavelength range ( nm): a two-body decay followed by the C—I bond dissociation in vibrationally hot radicals. Excitation at = 193 nm: molecular iodine formation CF 2 I 2 *  CF 2 + I 2 Huber and co-workers J. Chem. Phys. 1991, 1993, 1998 Roeterdink and Janssen J. Chem. Phys Radloff and co-workers J. Chem. Phys now near future

Absorption Spectra Can we reproduce T v (S 0 → S 1 )? Zheng, X. M.; Phillips, D. L., CPL 2000 LevelT v (S 0 → S 1 ) in nm (1) CAS(8,6)/3-21G ** (2) CAS(12,8)/Sadlej-pVTZ (3) CAS(12,8)/Sadlej-pVTZ //CASPT2/Sadlej-pVTZ (4) CAS(12,8)/Sadlej-pVTZ //CASPT2/ANO-RCC EXP (First Spectroscopic State) T1T1 S1S1 (1) (3) (4) (2) El-Khoury,Schapiro,Ryazantsev,Tarnovsky, Olivucci, JPC A 2009 submitted Previous Assignments

Absorption Spectra: CF 2 I 2 Nature of the Transition (S 0 → S 1 )? (1)(2)(3)(4) (5) (6) S0S0 S1S1 S0S0 S1S CAS(8,6)/3-21G ** This is NOT surprising! “CH 2 BrI”, Lindh and co-workers, CPC 2006 “CH 2 I 2 ”, Lindh and co-workers, CPC 2007

Mapping S 1 Basis Set? (6) (1) (7) (5) CAS(8,6)/3-21G ** adequate for a mechanistic study!

The Photochemical Reaction Path h El-Khoury, Tarnovsky CPL 2007

Changes in Geometrical Parameters along the Photochemical Reaction Path Zheng, Phillips, CPL 2000

The Conical Intersection: Characterization r = 0.4 S0S0 S1S1

The Conical Intersection: Branching Plane X -1 X Y -1 Y

Ultrafast Processes in Condensed-Phases: Dissociation Upon the promotion of a halomethane to an excited electronic state… The motion out of the Frank-Condon (FC) region. Solvent effects? Does this motion determine the rest of the excited/ground state minimum energy path? Multidimensionality! Solvent effects? Photochemical bond cleavage (Adiabatic vs diabatic). Solvent effects? How fast does it take to (re)combine nascent radical species? Solvent effects? Systems currently under the scope: Difluorodiiodomethane (CF 2 I 2 ) Iodoform (CHI 3 ) and Diiodomethane (CH 2 I 2 ) Towards reducing multidimensionality of space… DissociationEscape Recombination Trapping Vibrational relaxation Cooling Step 1: Mechanism (Problematic…Multiple Approaches) Step 2: Solvation dynamics

Photodissociation of CF 2 I 2 : F 2 C–I–I path 75 fs B1B1 El-Khoury, Olivucci, Tarnovsky Chem Phys Lett 2008

Small Molecule, Big Problem Future Directions B3LYP/Sadlej-TZVP MP2/Sadlej-TZVP CAS(12,8)/Sadlej-TZVP B3LYP/Sadlej-TZVP 2.68

Acknowledgments Collaborators Igor Schapiro (Olivucci Group) Mikhail N. Ryazantsev (Olivucci Group) Funding BGSU Prof. M. Olivucci BG SU Department of Chemistry Advisor Prof. A. N. Tarnovsky Resources OSC and LCPP

Species Relative Energy (in nm) CASSCF(8,6)/3-21G **a CASSCF(12,8)/Sadlej-pVTZ //CASPT2/Sadlej-pVTZ b CASSCF(12,8)/Sadlej-pVTZ //CASPT2/ANO-RCC c Relative Energy (in nm) RPA/B3LYP/3-21G *d Experimental e CF 2 I 2 -- CF 2 I 2 * (S 1 – Franck- Condon) 290 a 336 b 341 c n/a d 349 e, Assigned to T 1 CF 2 I 2 * (S 2 – Franck- Condon) 248 a 312 b 294 d, Assigned to S e, Assigned to S 1 Conical Intersection642 a n/a I ….. CF 2 I Van der Waals complex 674 a n/a