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Toward a Toward a “ “Polanyi Rule Polanyi Rule” ” Picture of Nuclear Picture of Nuclear Dynamics in Complex Polyatomic Ion Dynamics in Complex Polyatomic Ion-

• Molecule Reactions

Molecule Reactions

Jianbo Liu Department of Chemistry, Queens College & The Graduate Center, City University of New York

GRC on Gaseous Ions: Structures, Energetics and Reactions Galveston, TX, March 1-6, 2009

• 3.0
• 2.5
• 2.0
• 1.5
• 1.0
• 0.5

0.0 0.5

C2H2

+ + CH4

eV

C2H3

+(classical) +CH3

(H=0.23eV) C2H3

+(bridged) +CH3

(H=0.05eV)

+ +

TS2 C3H6

+

C3H5

+ + H (H=-0.93eV)

C3H4

+ + H2 (H=-1.32eV)

bridged complex classical complex TS1

2.01

2 . 1

1.25

1 . 4 5 1 . 2 2 1.87 1.23 1 . 5 6 1.66 1.66

Properties of the System  Early Time Dynamics

Hydrogen Abstraction! H or H2 Elimination!

Summary of Experimental Results

Collsion Energy (eV)

1 2 3 4

20 40 60

Cross Section (Å

2)

gs

C2H3

+

• Y. Chiu, H. Fu, J. Huang, and S. L. Anderson. JCP, 102, 1199(1995)

Excitation of C2H2

+ with two quanta

• f cis-bending (25

+, 0.155 eV)

25

+(cis-bending)

Time (fs)

100 200 300 400

Potential Energy (Hartree)

• 116.97
• 116.96
• 116.95
• 116.94
• 116.93
• 116.92

*

100 200 300 400

Distance (?

1.0 2.0 3.0 4.0 5.0

CH4 CH new CH CM dist turning point

* *

Direct Dynamics Simulations on C2H2+ + CH4: Nature and Time Scale of Nuclear Motions

H abstraction

• ccurs on rebound

50 fs  Set initial conditions using Hase’s VENUS (represent expt. conditions)

• Ecol : 0.5 eV
• Vibrational states: C2H2

+(gs and 25 +)

• Integrate trajectory using G03
• MP2/6-31+G* with “SCF=XQC” option

Trajectory Validation: Cross Sections & Product Ion Angular Distribution

Impact parameter b (?

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

P(b) x b

0.0 0.2 0.4 0.6 0.8 1.0 1.2

25

+

gs

1.6 12.6 8.1 traj 2.6 42 16 exp 25

+ state

Enhancement Ground state  (HA)

20 40 60 80 100 120 140 160 180

Axial Velocity (m/s) Radial Velocity (m/s)

• 1500
• 1000
• 500

500 1000 1500 500 1000 1500

C H

4

CH

+ 2 2

b=3.5 3.0 2.5 2.0 1.5 1.0 b=0.1 0.5

VCM

Opacity Functions for Hydrogen Abstraction

Trajectories qualitatively reproduce vibrational enhancement effects and angular distribution!

Trajectory Validation: Cross Sections & Product Ion Angular Distribution

Impact parameter b (?

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

P(b) x b

0.0 0.2 0.4 0.6 0.8 1.0 1.2

25

+

gs

1.6 12.6 8.1 traj 2.6 42 16 exp 25

+ state

Enhancement Ground state  (HA)

20 40 60 80 100 120 140 160 180

Axial Velocity (m/s) Radial Velocity (m/s)

• 1500
• 1000
• 500

500 1000 1500 500 1000 1500

C H

4

CH

+ 2 2

b=3.5 3.0 2.5 2.0 1.5 1.0 b=0.1 0.5

VCM

Opacity Functions for Hydrogen Abstraction

Trajectories qualitatively reproduce vibrational enhancement effects and angular distribution!

CM Frame Axial Velocity (m/s)

• 2500-2000-1500-1000 -500

500 1000 1500 2000 2500

Anderson's exp Ecol = 0.8 eV

<VCM>

traj calculated Ecol = 0.5 eV

Effects of C2H2

+ bending

H-C-C (degree)

60 90 120 150 180

Distribution Probability

0.0 0.1 0.2 0.3 0.4 0.5 ground state 25

+

H-C-C (degree)

60 90 120 150 180

Distribution Probability

0.0 0.1 0.2 0.3 0.4

H-C-C (degree)

60 90 120 150 180

Distribution Probability

0.0 0.1 0.2 0.3

At beginning of trajectories 25 fs before CM turning points at CM turning points

Distribution

• f C2H2

+

bend angle Cross section as a function Of bend angle

H-C-C (degree)

60 90 120 150 180

Contribution to Reaction

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 ground state 25

+

H-C-C (degree)

60 90 120 150 180

Contribution to Reaction

0.00 0.02 0.04 0.06 0.08 0.10

H-C-C (degree)

60 90 120 150 180

Contribution to Reaction

0.00 0.02 0.04 0.06 0.08 0.10

Distortion

?

rCH (Å) C2H2

+ bend angle (degree)

1 2 3 4 5 6

* Toward A “Polanyi-type” Picture for Polyatomic System

180 150 120 90

• 150
• 120
• 90

Saddle point Reactant Product

C C H H C H H H H

H-C-C plane

rCH

Ecol = 0.5 eV, and C2H2

+(gs)

rCH (Å) C2H2

+ bend angle (degree)

1 2 3 4 5 6

* Toward A “Polanyi-type” Picture for Polyatomic System

180 150 120 90

• 150
• 120
• 90

Reactant

Ecol = 0.5 eV, and C2H2

+(25 +) with Evib = 0.15 eV

Reactant Evib Reactant Ecol A+BC  AB+C Product Saddle point

Origins of Vibrational Effects on Reactions: Distortion vs. Momentum Acknowledgements Scott Anderson (U of Utah) ACS-PRF Grant CUNY Collaboration Grant

Biochemical ion Biochemical ion-

• molecule reactions

molecule reactions

+ 1O2