Chemistry Reference
In-Depth Information
TABLE 17.4
Experimental and Calculated Barrier Values and Mean Lifetimes of the
Isomerization 2O2(s) to 2O1(s)
Barrier,
Barrier,
Lifetime,
Lifetime,
Reference
Experimental
Calculated
Experimental
Calculated
(kJ mol
1
)
(kJ mol
1
)
(s)
(s)
-
11.7
-
-
[9]
10
14
-
5.9-8.6
-
from 2.9
[4]
10
10
-
-
-
to 8.8
-
10
12
-
-
>1
-
[5]
10
6
-
-
3.5
-
[3]
-
6.3
-
-
[10]
-
11
-
-
[8]
-
9.03
2.1
-
-
[11]
-
12
-
-
[12]
0.24-4.6
10
12
-
8.4-16.8
-
[32]
4
10
14
to 2
10
13
8.5
-
-
[13-15]
-
3.8
-
-
[34]
230
a
-
-
-
[35]
-
33.5
-
-
[36]
a
From the triplet state.
17.3 C
3
H
2
ISOMERS
17.3.1 I
NTRODUCTION
Isomers of C
3
H
2
are of great interest because of their unique chemical pro-
perties and because at least two of these are known to occur abundantly in
interstellar molecular clouds [37-42]. Several investigators have studied
properties of C
3
H
2
isomers both experimentally and theoretically (references
in remainder of text). Three isomers have been synthesized, namely triplet
propenylidene (also known as propargylene) 3O1(t), singlet cyclopropeny-
lidene 3C1(s), and singlet propadienylidene (also known as vinylidenecar-
bene) 3O2(s) [43-45]. Theoretical calculations have shown that a fourth
isomer triplet, trans-propenediylidene 3O3(t) (trans with regards to the
hydrogen atoms), has a true minimum energy on the C
3
H
2
potential surface
but it is much less stable than the other isomers [46]. Several investigators
have studied cyclopropyne, the cyclical C
3
H
2
molecule with both hydrogen
atoms bonded to the same carbon atom of the ring [43-50]. However,
neither a singlet, nor a triplet ground state of cyclopropyne has a true
minimum energy on the C
3
H
2
potential. A fourth open construct with both
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