Silver Nyambo Department of Chemistry, Marquette University, Wisconsin Reactive pathways in the chlorobenzene-ammonia dimer cation radical: New insights from experiment and theory 69 TH ISMS, June 2014

 Studying Non-Covalent Interactions using R2PI coupled with linear TOFMS  We use halobenzenes as convenient chromophores in prototypical systems:  Hydrogen bonding  π – π stacking  C-H/ π  N-H/ π  Halogen bonding  In this study: C 6 H 5 CI···NH 3 dimer Background

R2PI Experimental Details

Tonge; MacMahon; Pugliesi; Cockett. J. Phys. Chem 126, (2007) MP2/aug-cc-pVDZ level Previous work: FB-NH 3

Vaupel; Brutschy; Tarakeshwar; Kim. J. Am. Chem. Soc. 2006, 128, Previous work:  Vaupel et al- IR/R2PI-depletion spectroscopy in the N-H stretching region of NH 3 complexes and ab initio calculations o Compared experimental shifts from free NH3 absorptions, assigned out of plane structure

Remaining open questions 1.What is the structure of the C 6 H 5 CI···NH 3 dimer complex: in-plane σ- type or π – type? 2.The C 6 H 5 CI···NH 3 dimer is reactive upon ionization, – What reaction pathways are possible? 3.What are the branching ratios between competing reaction pathways?

DimerM06-2X/aug- cc-pVTZ CCSD(T)//M06- 2X/aug-cc-pVTZ D D D D PhCI---NH 3 optimized structures and calculated BE(kJ/mol) D1 D2 D3 D4

Calculated vertical absorptions-TD-DFT D3 D1 D2 D4 PhCl PhCl -NH 3

Franck-Condon Simulations Experiment σ- type π - type

The reactive 1:1 dimer Clbz-(NH 3 ) 3 Clbz-(NH 3 ) 2 Clbz-NH 3 Clbz AnH Aniline Ph-NH 2 +· PhCl···NH 3 +· Ph-NH 3 +

The Reaction Pathways via Wheland intermediates The reaction pathways are considered to proceed via two possible Wheland intermediates C 6 H 5 CI···NH 3 → (C 6 H 5 CI···NH 3 ) +· → (C 6 H 5 CI−NH 3 ) +· → (C 6 H 5 NH 3 ) + + CI · (1) → (C 6 H 5 NH 2 ) +· + HCI (2) → (C 6 H 4 CINH 3 ) + + H · (3) WH1-ipso-substitution WH2-ortho substitution

Reaction Pathway One - Cl atom loss +·+· TS1? Garvey et al J. Phys. Chem. 1994, 98,

Corresponding IRC Calculations for Cl and HCl loss IRC calculations suggest Cl loss and HCl loss occurs competitively from WH1 We optimized a four-center TS leading to HCl loss that lies 25kJ/mol above WH1 IRC calculations suggest Cl loss and HCl loss occurs competitively from WH1 We optimized a four-center TS leading to HCl loss that lies 25kJ/mol above WH1

HCl loss : Cl loss branching ratios from WH1 To quantify the branching ratios- Microcanonical TS theory (CHEMRATE) was used Cl loss channel predominates due to its lower barrier H atom loss channel is energetically inaccessible via our 2-photon energy WH2 either decays back to the ionized complex or it photo- dissociate via H loss Exp (HCl : Cl) - 1 : 5.4 Calc (HCl : Cl) - 1 : 5.6

Summary The dimer complex was assigned to the in-plane σ-type geometry We identified 3 channels by which the reaction path of the dimer may follow – The predominant reaction channel is the Cl atom loss – The HCl and H atom loss TS linking WH intermediates to the products were found computationally for all channels and were confirmed by IRC calculations Microcanonical TS calculations found the branching ratio of Cl : HCl loss to be 1 : 5.6, in accurate agreement to our experimental ratio (1 : 5.4)

Advisor: Scott A. Reid Group members: Brandon Lloyd Aimable Acknowledgements