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 (CH2)2.

A proposed structure for C60H36incorporating 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 C36H36'spheriphane' molecule.

A systematic search reveals five C78fullerene cages with isolated pentagons, but only one with a closed electronic shell, as predicted by Fowler's leapfrog rule. The closed-shell isomer has D3hsymmetry and is the most likely candidate for the structure of C78. Like C70, it corresponds to an expansion of the C60structure by insertion of an equatorial belt of hexagons.

The ground-state rotational spectra of the three symmetric-top isotopomers (CH3)314N ⋯HC14N, (CH3)314N⋯HC15N, and (CH3)314N⋯DC15N of a hydrogen-bonded dimer formed from trimethylamine and hydrogen cyanide have been investigated by pulsed-nozzle, Fourier-transform microwave spectroscopy. The spectroscopic constants B0, DJ, DJK, χ(14N1), and χ(14N2) have been determined from analyses of the spectra and for the isotopomer (CH3)314N⋯HC14N 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 (CH3)314N⋯HC14N: r(N⋯C) = 3.1035(6) Å, the subunit oscillation angles θav= 13.4(2)°, and φav= 9.1(4)° for the (CH3)3N and HCN subunits, respectively, and the hydrogen bond stretching force constant kσ= 14.7(2) N m-1. The opportunity has been taken to determine a more accurate value χ0(14N) = -5.5024(25) MHz for the14N-nuclear quadrupole coupling constant of free (CH3)314N. The properties of the family of dimers R3N⋯HX, where R = CH3or H and X = CN or CCH, are compared. © 1988 American Institute of Physics.