The determination of rotational and centrifugal distortion constants for eight isotopomers of a weakly bound complex of thiirane and ethyne was discussed. The nonlinearity of the hydrogen bond was attributed to a weak primary interaction S···H-C coupled with a secondary interaction involving the π bond of ethyne with the two equivalent H atoms of thiirane that were closest to it. The analysis also showed the comparison of the angular geometry of (CH 2 ) 2.

A proposed structure for C 60 H 36. incorporating four aromatic benzene rings has chiral T point group symmetry, involves less disruption of the parent fullerene skeleton, gives a better delocalisation energy, and is more closely compatible with experimental evidence than previous candidates; it is also analogous to the recently characterised C. 36 H 36. 'spheriphane' molecule.

A systematic search reveals five C 78. fullerene cages with isolated pentagons, but only one with a closed electronic shell, as predicted by Fowler's leapfrog rule. The closed-shell isomer has D 3h. symmetry and is the most likely candidate for the structure of C 78. Like C 70 , it corresponds to an expansion of the C 60. structure by insertion of an equatorial belt of hexagons.

The ground-state rotational spectra of the three symmetric-top isotopomers (CH 3 ) 3 14 N ⋯HC 14 N, (CH. 3 ) 3 14 N⋯HC 15 N, and (CH. 3 ) 3 14 N⋯DC 15 N of a hydrogen-bonded dimer formed from trimethylamine and hydrogen cyanide have been investigated by pulsed-nozzle, Fourier-transform microwave spectroscopy. The spectroscopic constants B 0 , D J , D JK , χ( 14 N 1 ), and χ( 14 N 2 ) have been determined from analyses of the spectra and for the isotopomer (CH. 3 ) 3 14 N⋯HC 14 N take the values 1373.6236(2) MHz, 0.694(10) kHz, 98.52(2) kHz, - 5.061 (14) MHz, and - 4.533(16) MHz, respectively. The spectroscopic constants have in turn been interpreted with the aid of a model of the dimer to yield the following molecular properties for the species (CH 3 ) 3 14 N⋯HC. 14 N: r(N⋯C) = 3.1035(6) Å, the subunit oscillation angles θ av. = 13.4(2)°, and φ av. = 9.1(4)° for the (CH 3 ) 3 N and HCN subunits, respectively, and the hydrogen bond stretching force constant k σ. = 14.7(2) N m. -1. The opportunity has been taken to determine a more accurate value χ 0 ( 14 N) = -5.5024(25) MHz for the. 14 N-nuclear quadrupole coupling constant of free (CH. 3 ) 3 14 N. The properties of the family of dimers R 3 N⋯HX, where R = CH 3. or H and X = CN or CCH, are compared. © 1988 American Institute of Physics.