Week 6. Some Tricks of Doing PES Calculations PES = Potential Energy Surface

F2 + CH3SCH3 (DMS) ReactionReaction between two Closed Shell moleculesM-M ReactionUsually a closed-shell molecule does not like to react with another closed-shell one. J. Chem. Phys. 127, 101101 (2007)

Closed Shell means thatthe configuration of doubly occupied molecular orbitals predominate.Usually a molecule with closed shell electronic structure is more stable and easier to be calculated.

Atom, Molecule & RadicalHCNOFNeMoleculeOHHFHH2NH3H2OHFCH4RadicalChemical ReactionAtom2 or 8 electrons(Octet)1 or 7 electrons(1 unpaired)HCNOFNe++

7.8 eV8.7 eV8.7 eV

Geometry: CAS-PT2 & QCISD(T) /cc-pVDZ (C,H); cc-pV(T+d)Z (S); aug-cc-pVTZ (F) Energy (kcal/mol): CCSD(T) & CAS-PT2 / Complete Basis Set Extrapolation for S, F.

F2 +F +No aug-basis on FEffect of Basis Sets

2.521.49SFF=173oCSF=90oS-C=1.807CSC=99oTS11.42 F2DMSS-C=1.806CSC=98oVDWCSF=87oS-C=1.807CSC=98o1.452.76SFF=171oSFF=170oCSF=91o S-C=1.794CSC=100oINT1.921.78(CH3)2SFCSF=89oS-C=1.788CSC=101o2.00Similar (CH3)2S structures Smaller basis sets for C and H are OK.The error will be canceled in the relative energy.

FF-S(CH3)2 distance ()F-FS(CH3)2 distance ()2-D PES with fixed (CH3)2S geometry

(CH3)2S + F2 (CH3)2SF + F INTPE profile on the reaction coordinate

three-center four-electron bondingINTe eF-Fss*e ess*ne e

1.901.83H-F: 1.95TS2 is Very Special!Free HF bond distance = 0.92for transition states: typical H-F distance = 1.1~1.4

Charge on FoutF-H distance ()Dipole(z) (atomic unit)INTTS2

F + CH3SFCH3 HF + CH2SFCH3Vertical IE of CH3SFCH3 = 7.8 eVElectron Affinity of F = 3.5 eV4.3 eVCH3SFCH3+ + F-CH3SFCH3 + F3.4Auto Charge Separation (Harpoon) mechanism-1/R

INTTS2CH2-S=1.621S-CH3=1.793 F-S=1.792CSC=103oFS(CH3)=88oFS(CH2)=117oCH2SFCH3~ F -Covalent or Ionic?

F2 + DMS0.0-100.6SF2(CH3)2CH3 + CH3 + -29.0-14.8Rel. Energy (kcal/mol)

One more thing about M-M Reaction

F2 + CH3-S-S-CH3 CH3SF + CH3SF, Barrier 4kcal/molCH3SF+CH3SS(F)CH3+from CH3S2FCH3

Proposed mechanismSSFFH3CH3C

Exp:Yu-Ju Lu (), Lance Lee(), Dr. Chu Shuan Chang (), H-J Shao (), Chi-Wei Liang(), , Cal: James Pan (), Dr. Tingxian Xie (), Prof. Henryk Witek

Prof. Yuan T. Lee, Prof. Yuan-Pern Lee

NSRRC for beam-time and help from Dr. Shih-Huang Lees group

$$$: Academia Sinica, NSC

Acknowledgement

Potential Energy SurfaceProduct DistributionThank You for Your Attention