ralf i. kaiser department of chemistry university of hawai’i at manoa honolulu, hi 96822
DESCRIPTION
Probing the Reaction Dynamics of Hydrogen-Deficient Hydrocarbon Molecules and Radical Intermediates via Crossed Molecular Beams. Ralf I. Kaiser Department of Chemistry University of Hawai’i at Manoa Honolulu, HI 96822 [email protected]. Introduction. CH x C 2 H x C 3 H x C 4 H x - PowerPoint PPT PresentationTRANSCRIPT
Ralf I. KaiserDepartment of Chemistry
University of Hawai’i at ManoaHonolulu, HI [email protected]
Probing the Reaction Dynamics of
Hydrogen-Deficient Hydrocarbon Molecules and Radical Intermediates
via Crossed Molecular Beams
Introduction
CHx
C2Hx
C3Hx
C4Hx
C5Hx
HC
HC
CH
CH
CH
C
HC
HC
CH
CH
CH
HC
CHHC
HC
CH
CH
Introduction
k = 10-11 – 10-12 cm3s-1 T < 1500 K
Eact = 5 – 45 kJmol-1
H3C H
H
H
H
H
H H
methylacetylene
acetyleneethylene
benzene
H
•
H
H
H
allene
H
H
CH3
H
propylene
Objectives
Investigate the Dynamics and Energetics of Phenyl Radical Reactions
Requirements
1. Preparation of Highly Reactive Reactant Radicals C6H5(X2A1)
2. Identify Reaction Products and Infer Reaction Intermediates
3. Obtain Information on Energetics and Reaction Mechanisms
↓
Single Collision Conditions
Crossed Molecular Beams Experiments
C6H5NO C6H5 + NO
< 0.1 % He seeded
200 Hz; 2800 – 3400 ms-1
ΔT
Crossed Molecular Beams Setup
Main Chamber = 10-9 torr
Detector = 10-11 - < 10-12 torr
1. Hydrocarbon Free
Requirements
2. Extremely Low Pressures
3. Signal Maximization
+
C6H5 + C2H2
77 amu 26 amu
C8H7 103
C8H7 + H 102 + 1
C8H6 + H2 101 + 2
+
C6H5 + C2D2
77 amu 28 amu
C8H5D2 105
C8H4D2 + H 104 + 1
C8H5D + D 103 + 2
C6H5 + C2H2 C8H6 + H (m/z = 102)
C6H5 + C2H2 C8H6 + H (m/z=102)
indirect reaction via intermediate exit barrier
Emax = Ec - rG
C6H5 + C2H2 C6H5CCH (m/z = 102) + H
+
Rel
ativ
e E
nerg
y, E
(kJ
/mol
)
25
50
0
-25
-50
-175
-125
-100
-75
-150
C6H5+C2H2
-36
-169
15
-90
X. Gu, F. Zhang, Y. Guo, R.I. Kaiser, Angew. Chemie Int. Edition 46, 6866 (2007).
C6H5 + C2H4 C8H8 + H (m/z=104)
C6H5 + C2D4 C6H5C2D3 + D (m/z=107)
C6H5 + C2H4 C6H5C2H3 + H (m/z=104)
indirect via intermediateexit barrier
Rel
ativ
e E
nerg
y, E
(kJ
/mol
)
25
50
0
-25
-50
-175
-125
-100
-75
-150
C6H5+C2H4
-30
-151
10
-50
C6H5 + C2H4 C6H5C2H3 + H (m/z=104)
F. Zhang, X. Gu, Y. Guo, R. I. Kaiser, J. Organic Chem. 72, 7597 (2007).
C6H5 + H2CCHCH3 C9H10 + H (m/z=118)
C6H5 + H2CCHCH3 C9H10 + H
C6H5 + C2H3CH3 C9H10 + H
Rel
ativ
e E
nerg
y, E
(kJ
/mol
)25
50
0
-25
-50
-175
-125
-100
-75
-150
C6H5+C3H6
9
25
0
19
-130
511
24
0
F. Zhang, X. Gu, Y. Guo, R.I. Kaiser, JPCA 112, 3284 (2008).
Phenyl Radical Reactions
Acetylene Ethylene Methylacetylene Allene Propylene Benzene
80 – 185 kJmol-1
Phenyl Radical Reactions
0
20
40
60
80
100
120
C.M.
(A)
0
20
40
60
80
100
120
C.M.
0
20
40
60
80
100
120
C.M.
(D)
(B) (E)
(C) (F)
Rel
ativ
e In
tens
ity (
arb.
uni
ts)
0
20
40
60
80
100
120
C.M.
0 5 10 15 200
20
40
60
80
100
120
C.M.
Lab Angle , (degree)
0 5 10 15 20 25 30 35 40 900
20
40
60
80
100
120
C.M.
Phenyl versus Hydrogen Exchange
Phenyl Group Stays Intact
Partially Deuterated ReactantsIsomer-Selective Detection
Abstraction Reactions < 5 %
Phenyl Radical Reactions
0.0
0.2
0.4
0.6
0.8
1.0 (A)
0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
(D)
(B) (E)
(C) (F)
P (
ET)
0.0
0.2
0.4
0.6
0.8
1.0
0 40 80 120 160 2000.0
0.2
0.4
0.6
0.8
1.0
Product Translational Energy ET, (kJmol-1)
0 40 80 120 160 200 2400.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
(A)0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
(D)
(B) (E)
(C) (F)T
()
0.0
0.2
0.4
0.6
0.8
1.0
0 30 60 90 120 1500.0
0.2
0.4
0.6
0.8
1.0
Center of Mass Angle , (degree)
0 30 60 90 120 150 1800.0
0.2
0.4
0.6
0.8
1.0
Indirect Reaction via Intermediates
Short Lived Intermediates (no ring closure)
Exit Barriers for Hydrogen Loss
Exoergic / Slightly Endoergic
Phenyl Radical Reactions
trans-1,3-butadiene 1,2-butadiene
2-butyne 1-butyne
Phenyl Radical Reactions
1-phenyl-1,3-butadiene (from 1,3-butadiene)
1-phenyl-butyne-21-phenyl-3-methylallene (from 1,2-butadiene) (from 1,2-butadiene)
1-phenyl-1-methylallene (from 2-butyne)
1-phenyl-3-methylallene (from 1-butyne)
1-phenyl-1-butyne (from 1-butyne)
Outlook
indene; C9H8 dihydroindene; C9H10
naphthalene; C10H8didehydronaphthalene; C10H6 dihydronaphthalene; C10H10
C6H5NO C6H5 + NOh (266 nm; 248 nm)
vp = 1800 – 2100 ms-1; EC = 30 – 50 kJmol-1
C2(X1g+/a3u) + C4H6 (1,3-butadiene)
C2 + C4H6 C6H5 + H Ec = 13 kJmol-1
C2(X1g+/a3u) + C4H6 (1,3-butadiene)
C2 + C4H6 C6H5 + H Ec = 36 kJmol-1
C2 + C4H6 C6H5 + H
phenylacyclic
H2CCDCDCH2 D2CCHCHCD2
C2 + C4H6 C6H5 + H
C2D + C4H6 C6DH5 + H
H2CCDCDCH2 D2CCHCHCD2
Ec = 45 kJmol-1
C2D + C4H6 C6DH5 + H
43 ± 10 %57 ± 10 %
C2D + C4H6 C6DH5 + H
rela
tiv
e e
ne
rgy
, k
Jm
ol-1
Outlook
EC = 80 – 185 kJmol-1
EC = 13 – 45 kJmol-1
EC = 30 - 50 kJmol-1
N
Outlook
Outlook
Acknowledgements