Post on 20-Dec-2015
transcript
Feng Zhang, Theodore S. Dibble
Chemistry Department, State University of New YorkCollege of Environmental Science and Forestry (SUNY-ESF)
Impact of tunneling on H-migration of n-propylperoxy radical
ICCK, MIT, 07/10/2011-07/14/2011
RH + ▪ OH
R▪
HO2 + alkene
O2 O2
ROO▪
QOOH
▪OH + products ▪OOQOOH
O2
2▪OH + products
Scheme of alkane auto-ignition (<1000 K)
H-migration
HO2 elimination
(or ▪H, O)
tunneling
)()()( TkTTk clQM
Goals
Tunneling treatment in literature: 1D model (Wigner or Eckart)
Use multidimensional treatment to get tunneling right;
Give guidance on 1D tunneling models for peroxy radicals.
OO
HO2
OOH
OOH
+
..
. 1, 5 H-migration
1, 4 H-migration
HO2 elimination
(R1)
(R2)
(R3)
Tunneling treatments
V0
V1
~Wiger
),,(~ 10 VVEckartEckart
~~
Reaction coordinate
V
VMEP
ZPE
VaG
~~
Reaction coordinate
V
VMEP
ZPE
VaG
),(~ curvatureV GamultiDDmulti
Methodologies
Benchmark: CCSD(T)/maug-cc-pVTZ//M052X/6-311+G(2df,2p)
1. Ab initio calculations
2. Tunneling treatment and rate constant calculation
VaG requires vibrational analysis along the whole path!
Select DFT method based on the benchmark
Calculate rate constants with multidimensional tunneling
Select DFT and basis set with least error
0.0
0.5
1.0
1.5
2.0
2.5
M05
2X/6-
31+G(d
,p)
M05
2X/6-
31+G(2
df,2p)
M05
2X/6-
311+
G(2d,2p
)
M05
2X/M
G3S
M06
2X/6-
31+G(d
,p)
M06
2X/M
G3S
B3LYP/M
G3S
B3PW
91/M
G3S
BMK/M
G3S
MPW
3PBE/M
G3S
B1B95
/MG
3S
CAM-B
3LYP/M
G3S
CBS-QB3
Mea
n U
nsi
gned
Err
or(k
cal/
mol
)
1,5 H-migration
1,4 H-migration: B3LYP/MG3S
HO2 elimination: B1B95/MG3S
1,5 H-migraion: M052X/MG3S
MG3S=6-311+g(2df,2p) for C,H, O
The “lucky” benchmark
1,5 H-migration 1,4 H-shift HO2 elimination method
E0 Erxn MUE E0 Erxn MUE E0 Erxn MUE
Focal pointa 24.5 16.1 0.0 32.7 13.4 0.0 30.1 17.5 0.0
CCSD(T)/maug-cc-PVTZb
24.7 16.1 0.1 33.2 13.9 0.5 30.1 16.8 0.3
M052X/MG3S 25.3 17.3 1.0 35.1 14.4 1.7 33.9 19.3 2.8
B3LYP/MG3S 24.5 18.7 1.3 33.0 14.6 0.7 26.9 14.1 3.3
B1B95/MG3S 24.6 20.0 2.1 32.7 16.5 1.5 29.1 16.2 1.1
CBS-QB3 23.8 15.9 0.4 32.1 13.7 0.4 30.90 18.2 0.7
a From Prof. Allen’s talk this morning!
Reaction paths
TS-15 (1836 cm-1)
TS-14 (2172 cm-1)
TS-e (1027 cm-1)
1
3
5
7
9
500 600 700 800 900 1000
T(K)
Tun
neli
ng c
oeff
icie
nt
R3
Multidimensional tunneling coefficients
R1
R2
OO
HO2
OOH
OOH
+
..
. R1
R2
R3
cl
QM
k
k
Comparison of tunneling treatments for 1,4 H-migration
Comparison of tunneling treatments for 1,5 H-migration
Reaction coordinate (amu1/2*Å)
Rate constants in the high pressure limit
SRG: J. Phys. Chem. A 114, 5689, 2010
HCD:J. Phys. Chem. A 114, 6594, 2010
Summary
High pressure limiting rate constants were computed for H-migration, HO2 elimination of n-propyl peroxy radical.
Wigner’s formula largely underestimates tunneling. Eckart potential gives reasonable predictions.
First multidimensional tunneling treatment of these reactions in alkyl peroxy radical
Acknowledgements
Prof. Donald G. Truhlar, Dr. Jingjing Zheng
U.S. Department of Energy
Thanks for your attention!
Internal rotation in CH3CH2CH2OO▪
Reactant TS-15s TS-14s TS-e
)(
)()(
tanRe TQ
TQTk
tac
TS
-200
0
200
400
600
800
1000
Hindered rotor treatment
Torsion Eigenvalue Summation(TES) method
n
nm
m nBmAAV sincos)( 0
0
200
400
600
800
1000
0 60 120 180 240 300 360
Torsional angle(degree)
Poten
tial En
ergy(cm-1)
0
1
2
3
4
5
-2 0 2 4 6
logP(Torr)
500 K
700 K
1,4 H-shift
1,5 H-shift
logΓ
Pressure dependence of Eckart tunneling coefficient
1atm