Page 301 - Academic Press Encyclopedia of Physical Science and Technology 3rd Analytical Chemistry

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Encyclopedia of Physical Science and Technology EN009N-447 July 19, 2001 23:3

818 Microwave Molecular Spectroscopy

TABLE X Structures and Preparation Methods of Some Unstable Molecules a
Structure Reference
Linear b Cooper, T. A., Firth, S., and Kroto, H. W. (1991). J. Chem. Soc. Faraday Trans. 87, 1499
1 . 284 1 . 606
F B S
Linear b Cooper, T. A., Firth, S., and Kroto, H. W. (1991). J. Chem. Soc. Faraday Trans. 87, 1
1 . 831 1 . 608
Br B S
Symmetric top c Ahmad, I. K., Ozeki, H., and Saito, S. (1991). J. Chem. Phys. 110, 912
H
114 . 26
1 . 4406 P O
1 . 4763
H
H
Planar d Bailleux, S., et al. (1997). J. Chem. Phys. 106, 10016
H 122 . 00 122 . 39 H
1 . 0819
C Si
1 . 7039 1 . 4671
H H
e
Debridged (butterfly) Bogey, M., Bolvin, H., Cordonnier, M., Demuynck, C., Destombes, J. L., and Csaszar, A. G.

HSi SiH 104.22 (1994). J. Chem. Phys. 100, 8614
H
H
1 . 6680

Si
Si
2 . 2154
Planar f Fujitake, M., and Hirota, E. (1997). J. Mol. Struct. 413, 21
Si
1 . 5960 2 . 0714
F 100 . 85 Cl
Planar g Tsuchiya, M. J., Honjou, H., Tanaka, K., and Tanaka, T. (1995). J. Mol. Struct. 352, 407
Ge
2 . 16945
99 . 883
Cl Cl
a Bond lengths in angstrom units, bond angles in degrees.
b Prepared by passing FSSF or BrSSBr vapor over crystalline boron chips at ca. 1100 C.
◦
Reaction product introduced directly into the microwave cell and rapidly pumped through the cell (fast pumping) [r s ].
c Prepared in situ by a dc glow discharge of a mixture of PH 3 ,CO 2 , and H 2 [r 0 ].
d Prepared by a pyrolysis reaction, equilibrium structure [r e ].
e Prepared by dc glow discharge of SiH 4 in Ar [ r ].
f Prepared by fast pumping using pyrolysis on a mixture of compounds [ r ].
g Prepared by fast pumping and a dc glow discharge of GeCl 4 [r e ].

(see Section VIII). The isotopic species data provide the H C C C C C C C C C N,
Cartesian coordinates of the atoms in the molecule’s prin-
cipal axis system. For HC 5 N, the spectra of eight isotopic was first detected in interstellar space. It was thought that
species were studied in natural abundance. The above se- this molecule would be very difficult to produce and mea-
ries also nicely illustrates delocalization effects in such sure in the laboratory. However, it has now been observed
conjugated systems. In going from HC 3 NtoHC 5 N, de- in the laboratory by discharging a mixture of vinylcyanide
localization lengthens the triple bonds and shortens the andacetylenedilutedinargonfollowedbyrapidexpansion
single bonds. into a cavity spectrometer which stabilizes the molecule.
Other members of these linear carbon chains have also The methylcyanopolyynes, CH 3 (C C) n CN, like the
been measured. The unstable linear carbon chain molecule cyanopolyynes, H(C C) n CN, are of interest both for
HC 9 N, possible detection in interstellar space and for testing