1. Effects of Reactant Rotational excitation on Cl + CH 4 / CHD 3 Reactions Speaker: Huilin Pan Supervisor: Kopin Liu 69 th ISMS, June 16-20, 2014

2. Reactant rotation: a key to stereodynamics Disentangle the stereodynamical properties experimentally Rationalize the reaction stereodynamics mechanism Cl + CHD 3 (v 1 =1, JK)  HCl + CD 3 Cl + CH 4 (v 3 =1, JNl)  HCl + CH 3

3. Energy levels involved in optical transition of methane CH 4 (ν 3 = 1, JNl) Herzberg, 1945; Chem. Phys., 2009,356,131; Phys. Chem. Chem. Phys., 2014, 16, 444 Research background on Cl + methane reaction J – total angular momentum N – rotational angular momentum l – vibrational angular momentum J = N + l Selection rule: ΔN = 0 |JNl> P(1) |01-1> Q(1) |110> R(0) |101> R(1) |211> R(2) |321>

4. Energy levels involved in optical transition of methane CHD 3 (ν 1 = 1, JK) Herzberg, 1945; Chem. Phys., 2009,356,131; Phys. Chem. Chem. Phys., 2014, 16, 444 Research background on Cl + methane reaction J – total angular momentum K – projection of J on C-H bond |JK> P(1) |0,0> Q(1) |1, ± 1> R(0) |1,0> R(1) |2,0>+|2, ± 1>

5. Experimental setup Rev.Sci.Instrum.2003,74,2495; Rev.Sci.Instrum.2008,79,033105 MCP + Phosphor CD 3 / CH 3 probe  ~333 nm Cl beam ICCD camera UV scan CHD 3 / CH 4 beam CHD 3 v 1 / CH 4 v 3 IR  ion packet Ion optics

6. Results of Cl + CH 4 (ν 3 =1, JNl) → HCl(ν) + CH 3 (ν=0) Raw images of R(0) branch 5.0 kcal/mol IR off IR on 2.0 kcal/mol  At same collision energies, similar images were obtained from reactants with different rotational states. CH 4 0∘0∘ 0∘0∘ 3.2 kcal/mol CH 4

7. Translational and angular distributions of different branches 5.0 kcal/mol  Similar translational and angular distributions. Results of Cl + CH 4 (ν 3 =1, JNl) → HCl(ν) + CH 3 (ν=0)

8. Integral cross section(ICS) of different branches  At High Ec, there is little diversity from rotationally excited reactants.  Ec~2kcal/mol, reactivity differs. Reactivity diversity rises from the entrance valley. The exit valley is the same. Results of Cl + CH 4 (ν 3 =1, JNl) → HCl(ν) + CH 3 (ν=0)

9. Integral cross section of different branches  The reactivity increases with the increasing total angular momentum.  The ICS of R(0) and Q(1) cross at around 2kcal/mol: above 2kcal/mol, reactivity of R(0) is in general bigger than Q(1); under 2kcal/mol, the situation is opposite. Results of Cl + CHD 3 (ν 1 =1, JK) → HCl(ν) + CD 3 (ν=0)

10. Reaction mechanisms on Cl + CHD 3 (ν 1 =1, JK) → HCl(ν) + CD 3 (ν=0) Origin of the reactivity diversity Cl H H D D D D H H C D D ?  More energy enhances reactivity effectively σ J /σ J=0 ~ 2 Nature Chem. 4, 636 (2012); J. Chem. Phys. 103, 7313 (1995); J. Phys. Chem. 91, 1400 (1987). CH 4 : R(2), J=3, ~ 63 cm -1 CHD 3 : R(1), J=2, ~ 20 cm -1 E c : 2 kcal/mol ~ 700 cm -1

11. Origin of the reactivity diversity: Short range forces Position of barrier Bending ⊥ reaction coordinate Late barrier: Saddle point, more product-like r ↑, BC’s moment of inertia ↑. The initial rotation helps to overcome the repulsive torque.  Enhance reactivity Early barrier: Saddle point, more reactant-like r unchanged. For J>0, the interactions tend to constrict the access to transition state.  Reduce reactivity Softer bend allows larger range of initial γ Rotational excitation enlarge γ, enhancing the reactivity The factor dominates in rotational reactivity diversity is not sure. Reaction mechanisms on Cl+CHD 3 (ν 1 =1, JK)  HCl(ν) +CD 3 (ν=0)

12.  In both reactions Cl + CH 4 (ν 3 =1, JNl) → HCl(ν) + CH 3 (ν=0) Cl + CHD 3 (ν 1 =1, JK) → HCl(ν) + CD 3 (ν=0)  Further investigations are needed to gain deeper insights Conclusion The translational and angular distributions keep the same at different reactant rotation. Integral cross sections change with reactant rotational states. Short-range interactions of reactants.

13. Acknowledgement

14. Methane’s angular momentum CH 4 (ν 3 =1)J’’N’’J’N’l’ P(1)1101 Q(1)11110 R(0)00101 R(1)11211 R(2)22321 CHD 3 (ν 1 =1)J’’J’K’ P(1)100 Q(1)111 R(0)010 R(1)121

15. Experimental setup and data analysis Experimental setup

16. Reaction mechanisms on Cl+CHD 3 (ν 1 =1, JK)  HCl(ν) +CD 3 (ν=0) Origin of the reactivity diversity: Long range forces Chem. Phys. 104, 213 (1986); Chem. Phys. 112, 85 (1987); J=1 --- ; J=3 - · - · ; J=5 ··· J=0 J>0 J=0 J>0

17. Reaction mechanisms of Cl + CH 4 (ν 3 =1, JNl) → HCl(ν)+ CH 3 (ν=0) Reaction mechanisms of two channels of HCl HCl (v=1) HCl (v=0) Cl H H C H H H H C H H J. Chem. Phys., 133, 124304 (2010); Proc. Natl. Acad. Sci. USA 105, 12667 (2008). H H H H H H H H H H H H  With the CH 4 reactant excited to different J at ν 3 =1, the translational and angular distributions are the same. Direct rebound Back/sideways Short-lived complex forward

18. PC (event counting)‏ MCP + Phosphor CD 3 / CH 3 probe  ~333 nm Cl beam ICCD camera UV scan CHD 3 / CH 4 beam CHD 3 v 1 / CH 4 v 3 IR  ion packet Ion optics Rev.Sci.Instrum.2003,74,2495; Rev.Sci.Instrum.2008,79,033105 Experimental setup Experimental setup and data analysis  Product pair correlation measurement IR laser multipass reflector

19. Well-defined imagingREMPI Energy conservation Momentum conservation Experimental setup and data analysis

20. Experimental setup Rev.Sci.Instrum.2003,74,2495; Rev.Sci.Instrum.2008,79,033105

21. IR off IR on Data Analysis Reactant CH 4 /CHD 3 Product CH 3 /CD 3 1 = S off = S on D + + S s = [S on – (1 – D)S off ] / D Results of Cl + CH 4 (ν 3 =1, JNl) → HCl(ν) + CH 3 (ν=0)

22. Obtaining the relative cross sections Depletion Test: F+CH 4 (v 3 =1, JNl)  HF+CH 3 (ν=0) F+CHD 3 (v 1 =1, JK)  DF+CHD 2 (ν=0) S s = [S on – (1 – D)S off ] / D Relative σ σ: integral cross section u: relative velocity [Cl],[CH 4 ]: molecular beam density DP(1)Q(1)R(0)R(1)R(2) CH 4 0.1350.2710.2340.33850.085 CHD 3 0.0450.1680.1050.245 Translational Angular Results of Cl + CH 4 (ν 3 =1, JNl) → HCl(ν) + CH 3 (ν=0)

23. Science 316, 1723 (2007); Proc. Natl. Acad. Sci. USA 105, 12667 (2008). ΔΗ 0 = 1.7 kcal/mol Barrier height ~4 kcal/mol Late barrier reaction Research background on Cl + methane reaction Schematics of the potential energy levels of Cl+CHD 3

24. Results of Cl + CHD 3 (ν 1 =1, JK) → HCl(ν) + CD 3 (ν=0) Raw images of R(1) branch at low collision energies 1.5 kcal/mol1.1 kcal/mol  Similar images were obtained from reactants with different rotational excitation of reactants at the same Ec. IR on CHD 3 0∘0∘ 0∘0∘

25.  Similar translational and angular distributions in these branches.  At low collision energy 1.5kcal/mol, the angular distribution of product pair (1,0 0 ) s spreads to the whole range. Translational and angular distributions of different branches 1.5 kcal/mol Results of Cl + CHD 3 (ν 1 =1, JK) → HCl(ν) + CD 3 (ν=0)