Page 300 - Academic Press Encyclopedia of Physical Science and Technology 3rd Analytical Chemistry

P1: GNH Final Pages
Encyclopedia of Physical Science and Technology EN009N-447 July 19, 2001 23:3

Microwave Molecular Spectroscopy 817

TABLE IX (Continued)

[ r ] Cox, A. P., Ellis, M. C., Attfield, C. J., and Ferris, A. C. (1994). J. Mol. Struct. 320, 91
O
1.213 115.7
H
HNO 3 N 102.6 0.941
1.198 1.410 O
114.1
O
[r e ] Esposti, C. D., Tamassia, F., Cazzoli, G., and Kisiel, Z. (1995). J. Mol. Spectrosc. 170, 582
N
2.144 1.133
Br 114.1 O
[r s ] Klesing, A., and Sutter, D. H. (1995). J. Mol. Struct. 352, 357
H
122.51
1.085
1.077 C 114.72 O
H 115.63 1.610 S 1.469
[r e ] Nakata, M., and Kuchitsu, K. (1995). J. Mol. Struct. 352, 219
H C C Cl
1 . 063 1.209 1.631
[r s ] Niedenhoff, M., Yamsda, K. M. T., Winnewisser, G., and Ross, S. C. (1995). J. Mol. Struct. 352, 423
H
123 . 9
0 . 9946 1 . 2140 1 . 1664
N C O
172 . 6

a Type of structure (see Section VIII) is given in brackets. Bond lengths are in angstrom units, bond angles ABC in degrees. See also references
cited.

and the scaled method, and critical evaluation of pre- results are obtained for the acetylene moiety in H 2 PC CH
dictive models should make use of these parameters if depicted in Fig. 13a. Here, the C CH group is bent away
possible. from the phosphine hydrogens by 7 . A small nonlinear-
◦
Numerous small structural effects have also been re- ity in the NCO, NCS, and N 3 chains is found in HNCO,
vealed by microwave structure studies. In this section a HNCS, HN 3 , and CIN 3 . Many other examples of slightly
few of these results are pointed out to provide the reader bent configurations have been found. Some are not easily
with an indication of what can be found from a study explained by simple bonding theory.
of the rotational spectrum. Also, some of the areas of Recent microwave measurements in the laboratory have
study are mentioned briefly to indicate the wide range aidedthedetectionofmanymoleculesininterstellarspace.
of problems being attacked by microwave spectroscopy. We mention here the linear cyanide chains,
Many detailed structures and molecular information other
than those mentioned here have been obtained, and the 1.0631
H C ≡≡≡≡≡≡ N,
reader should consult the Bibliography and references 1.155
cited therein for further examples. 1.058 1.378
H C ≡≡≡≡≡≡ C C ≡≡≡≡≡≡ N,
1.205 1.159
1. Selected Structural Information H 1.0569 C ≡≡≡≡≡≡ C 1.3623 C ≡≡≡≡≡≡ C 1.3636 C ≡≡≡≡≡≡ N,
1.2087 1.2223 1.1606
A careful study of the molecular structure by microwave
methods provides numerous interesting structural fea- which have been studied in the laboratory and also de-
tures. For example, it is apparent from Table III that the CF tected in interstellar space. Such observations in outer
bond in FCN is shorter than in FCP. Many observations of space provide the information from which theories on the
this nature have been made and often correlated with sim- mechanisms of formation of particular molecules can be
ple bonding theory. A different effect may be illustrated formulated and hence a better understanding gained of
by the C N chain in methylene cyanide, CH 2 (CN) 2 , and the development of the universe. The structures of the
sulfur dicyanide, S(CN) 2 , which is not linear, but rather is above molecules were obtained by studying various 13 C
15
bent slightly by about 3 and 5 , respectively. Such effects isotopic species as well as N and D species. Ideally, each
◦
◦
are not confined to the presence of a cyano group. Similar nonequivalent atom needs to be isotopically substituted