A Combined Theoretical and Experimental Study of the HF+CN F + HCN Reaction; The CN-HF Entrance...
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A Combined Theoretical and Experimental Study of the HF+CNF + HCN Reaction; The CN-HF Entrance channel complex Jeremy Merritt and Michael Heaven Department of Chemistry Emory University Atlanta, GA 30322
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Transcript of A Combined Theoretical and Experimental Study of the HF+CN F + HCN Reaction; The CN-HF Entrance...
A Combined Theoretical and Experimental Study of the HF+CNF + HCN Reaction;
The CN-HF Entrance channel complex
Jeremy Merritt and Michael Heaven
Department of ChemistryEmory UniversityAtlanta, GA 30322
A Combined Theoretical and Experimental Study of the HF+CNF + HCN Reaction;
The CN-HF Entrance channel complex
Department of ChemistryEmory UniversityAtlanta, GA 30322
Jeremy Merritt and Michael Heaven
Motivation
Weak van der waals forces can strongly influence dynamics Cl + HD; Roaming Hydrogen atom mechanism
HX-CN has been suggested as being important in controlling theproduct state distributions observed in X+HCN scattering
Multiple, asymptotically degenerate Potential energy surfaces can resultin breakdown of the Born-Oppenheimer approximation
Reaction dynamics at the quantum level 4 atom systems
Photoinduced reaction of entrance channel complexes impact parameter averaging
Aid in understanding future experimental results X, A, and B states of CN are convenient handles
-15000
-10000
-5000
0
5000
10000
15000
20000
H + ClCNHCl + CN
H + FCN
HF + CN
HBr + CNH + BrCN
G2
Ene
rgy
(cm
-1)
X + HCN
Exp
erim
enta
l
A global picture
Ab initio Calculations
Start with rigid monomers constrained to a common plane = Cs
[0.1, 180.1, 20.0] [0.1, 360.1, 20.0]
R [10.0, 6.0, 5.0, 4.5, 4.0, 3.75, 3.5, 3.25, 3.0, 2.75, 2.5 Å]
rHF = 0.9168 ÅrCN = 1.1718 Å
F
C
N
R
rHF
rCN
Performed using MOLPRO
(gas phase values)
C N
Basis set = Aug-cc-pVDZ+{332}
Methodology
1) RHF for 1A’ state
2) 4SA-CASSCF(7,8)
3) MRCI(7,7)
4) Counter-Poise Correction using
Davidson Energies
5) Correct for size consistency (20 Å)
CN – HF; What to expect
C N2
2*
3
x y
3
x* y*
X 2+
CN – HF; What to expect
C N2
2*
3
x y
3
x* y*
B 2+
CN – HF; What to expect
C N2
2*
3
x y
3
x* y*
A 2
2A’
A”
For Non-linear geometries
4SA-CASSCF(7,8)
1A”, 3A’
Tests on CN monomer
0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0
05000
1000015000200002500030000350004000045000500005500060000
Ene
rgy
(cm
-1)
rCN (Angstrom)
MRCI Exp.
X 2+ re (Å) 1.187 1.1718
A 2 Te (cm-1) 8734 9245.3
A 2 re (Å) 1.246 1.2333
B 2+ Te (cm-1) 27509 25752
B 2+ re (Å) 1.158 1.15
-1300
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600
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0 20 40 60 80 100 120 140 160 1800
60
120
180
240
300
360
(deg)
(de
g)
-1100
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-100200
0
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0 20 40 60 80 100 120 140 160 1800
60
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180
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360
(deg)
(de
g)
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300
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0 20 40 60 80 100 120 140 160 1800
60
120
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(deg)
(de
g)
900
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0
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0 20 40 60 80 100 120 140 160 1800
60
120
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(deg)
(de
g)
F
C
N
R = 3.5 Å
X 2+ B 2+A 2
A”
A’
FH--CN
FH--NC
HF--NCHF--CN
400300
200
1000
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100-300
0
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0100-300
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0 20 40 60 80 100 120 140 160 1800
60
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Y A
xis T
itle
X Axis Title
-900 -700
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0
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0
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0 20 40 60 80 100 120 140 160 1800
60
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Y A
xis T
itle
X Axis Title
F
C
N
R = 4.0 Å
X 2+ B 2+A 2
A”
A’
FH--CN
FH--NC
HF--NCHF--CN
-1000 -900 -700-500
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0 20 40 60 80 100 120 140 160 1800
60
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Y A
xis T
itle
X Axis Title
-1000 -800
-600 -500-400
-300-200
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-100
0
0
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100
0
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0 20 40 60 80 100 120 140 160 1800
60
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Y A
xis T
itle
X Axis Title
Theta = 0 degrees
F
C
N
R
400100
0
0
-100-300-1100
3 4 5 6 7 8 9 100
60
120
180
240
300
360
R (Angstrom)
(de
g)
100
100
-100-900
3 4 5 6 7 8 9 100
60
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360
R (Angstrom)
(de
g) 500 100
0
0
-100-1200
3 4 5 6 7 8 9 100
60
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360
R (Angstrom)
(de
g)
0
0
-100-900
3 4 5 6 7 8 9 100
60
120
180
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300
360
R (Angstrom)
(de
g)
F
C
N
R
100
0
0
-100
-100-300
-300
3 4 5 6 7 8 9 100
60
120
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240
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360
R (Angstrom)
(de
g)
0
0
-100
-100-300
-300
3 4 5 6 7 8 9 100
60
120
180
240
300
360
R (Angstrom)
(de
g)
0
0
-100-300
3 4 5 6 7 8 9 100
60
120
180
240
300
360
R (Angstrom)
(de
g)
100
0
0
3 4 5 6 7 8 9 100
60
120
180
240
300
360
R (Angstrom)
(de
g)
Theta = 180 degrees
Dihedral cut
F
C N
R = 3.5 Å
0 20 40 60 80 100 120 140 160 180
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0
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0
100
200
Ene
rgy
(cm
-1)
X A A B
A"
A'
Stationary points
FH---NC
FH---CN
HF---NC
HF---CN
X 2+ B 2+A 2
De = 1200 cm-1
Re = 3.4 ÅDe = 1000 cm-1
Re = 3.4 Årepulsive
repulsive
repulsive repulsive
repulsive repulsive
De = 1570 cm-1
Re = 3.6 Å
De = 1300 cm-1
Re = 3.6 Å
Re = 3.8 ÅDe = 330 cm-1
Small isomerizationbarrier
Small isomerizationbarrier
De = 330 cm-1
Re = 3.8 Å
Bent?
Bent?
0
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1.00 1.05 1.10 1.15 1.20 1.25 1.30 1.35 1.40-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
Ene
rgy
(cm
-1)
rCN (Angstrom)
X 2+
B 2+
A 2
Dip
ole
Mom
ent (
deby
e)
Why the geometry flip-flop?
1 2 3 4
0
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40000
Ene
rgy
(cm
-1)
rFH (Angstrom)
0.8655 0.9655 1.0655 1.1655 1.2655 1.3655 1.5 1.75 2.0 2.25 10.0
FH + CN (X 2+) F + HCN (2)
0.7 1.4 2.1
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rgy
(cm
-1)
rCH
rFH 0.7168 0.8168 0.9168 1.0168 1.1168 1.2168 1.3168 1.5 1.75 2 4 10
FH + CNF-HCN
Collinear FH-CN Reaction Path
HF bonding orbital (F 2Pz) was included into the active space
Hexp = 4046 cm-1H = 3125 cm-1
Summary and Conclusions• HF+CN PES is rich• Bound-Bound (Bound-Free) transitions
expected for A-X (B-X) excitation of FH--NC• Onset of continuum would accurately
probe ground state binding energy• ~7300 cm-1 barrier to reaction; should be
ammenable to jet cooling• Zewail type experiments?
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