1 Dynamics of Chemical Reactions and Photochemical Processes Yuan T. Lee Academia Sinica, Taipei, Taiwan

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16 m 1 u 1 = m 2 u 2 or m 2 / m 1 = u 1 / u 2 m 4, u 4 m 2, u 2 m 1, u 1 m 3, u 3 M=m1+m2=m3+m4M=m1+m2=m3+m4 m 3 u 3 = m 4 u 4 or m 4 / m 3 = u 3 / u 4

17 C 2 H 5 NO 2 ≠ HONO + CH 2 =CH 2

18 C 2 H 5 NO 2 ≠ C 2 H 5 + NO 2

19 Hexahydro-1,3,5-trinitro-1,3,5- triazine RDX HCN + HONO + NO 2 + N 2 O + H 2 CO + ‧ ‧ ‧ ‧ ‧ ‧ ‧ ‧ ‧ ‧ Δ N 2 + CO + H 2 O Questions 1. Dissociation Mechanism Unimolecular vs. biomolecular Primary and secondary dissociations 2.Dissociation Dynamics Modes of Energy Release X. Zhao E. Hintsa

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23 RDX 3CO + 3H 2 O + 3N 2 (3×) CH 2 =N-NO 2 HCN + HONO N 2 O + H 2 CO Concerted Steps High Temperature Combustion

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32 Quantum chemistry is developing in at least two directions. First, very large systems can now be studied using conventional methods, namely Hartree-Fock theory, density functional theory, and second-order perturbation theory. Structural optimizations including all geometrical degrees of freedom can now be completed for molecules with as many as 200 atoms. Frozen geometry computations (usually not very useful) can be carried out for systems of 1000 atoms. This work opens up a vast new expanse of chemistry for theoretical studies. F. Schaefer

33 Secondly, more and more rigorous new methods are emerging every year. These can be applied to smaller systems (perhaps up to the size of benzene) to yield what I call sub-chemical accuracy, reliability to 0.5 kcal/mole or better. As you know well, such energetic quantities are critical to combustion and environmental studies and in some cases are very difficult to determine from experiment. Among the newer methods, coupled cluster theory with all single, double, triple, and quadruple excitations, CCSDTQ, is becoming a viable technique. F. Schaefer

34 Especially important is the development of methods that explicitly include the inter-electronic coordinates R12. These ideas have been around since the famous work of Hylleraas on the He atom in However, it is only in the past five years that such methods have become useful for studying chemical systems. Also encouraging is that most of the work in this R12 area is being done by young people, for example Wim Klopper (Karlsruhe), Fred Manby (Bristol), and Edward Valeev (Virginia Tech). F. Schaefer

35 Basis Set Lowest a 1 mode / cm -1 Lowest b 2 mode / cm -1 cc-pVDZ615i93i cc-pVTZ621i40 CCSD(T) / cc-pVTZ transition state geometry Ortho-Benzyne decomposition, Simmonett, Allen, and Schaefer (2006)

36 Fully optimized geometries of 2’-deoxyriboadenosine 2’-deoxyribothymidine pair. J. Gu, Y. Xie, and H.F. Schaefer (2006)

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40 m 1 u 1 = m 2 u 2 or m 2 / m 1 = u 1 / u 2 m 4, u 4 m 2, u 2 m 1, u 1 m 3, u 3 M=m1+m2=m3+m4M=m1+m2=m3+m4 m 3 u 3 = m 4 u 4 or m 4 / m 3 = u 3 / u 4

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42 mv=F △ t=ma △ t =Constant=P =Constant=PE= m E m E -1

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44 Toluene I.C. + H + CH 3 193nm

45 m/e 15 CH 3 m/e 16 CH 2 D m/e 17 CHD 2 m/e 18 CD 3 m/e 76 m/e 77 C 6 H 5 m/e 78 C 6 H 4 D m/e 79 C 6 H 3 D 2 m/e 80 C 6 H 2 D 3 m/e 93 C 6 H 5 CD 2 m/e 94 C 6 H 4 DCD 2 m/e 95 C 6 H 5 CD 3 m/e 96 Velocity Axis Mass Axis Photodissociation of C 6 H 5 CD 193 nm J. Am. Chem. Soc. 124, 4068 ( 2002 )

46 Energy diagram of isomers and photoproducts of C 6 H 5 CH 3 DFT CCSD C 6 H 5 CH 2 + H

47 Comparison of Photoisomerization Mechanisms Early Discovery: Ring Permutation (in 1960s) h h 193nm New Observation: Seven-Membered Ring Pathway C 6 H CH 3 C 6 H 5 + CD 3 C 6 H 4 D+CD 2 H Also C 6 H 3 D 2 +CDH 2 C 6 H 2 D 3 +CH 3 C 6 H 5 +CD 3 C 5 13 CH 5 +CH 3 Also C 6 H CH 3

48 h 193nm h H, NH 2 H, CH 3 CH 3 NH 2 C 6 NH 7