Collect. Czech. Chem. Commun. 1979, 44, 3458-3463

The dimer (HCl)2: Stationary points on the SCF 4-31G energy hypersurface and the role of entropy in the dimer formation

Pavel Hobzaa, Petr Čárskyb and Rudolf Zahradníkb

a Institute of Hygiene and Epidemiology, Centre of Industrial Hygiene and Occupational Diseases, 100 42 Prague 10
b J. Heyrovský Institute of Physical Chemistry and Electrochemistry, Czechoslovak Academy of Sciences, 121 38 Prague 2


Two stationary points have been investigated on the 4-31G SCF energy hypersurface of (HCl)2. It has been shown, in agreement with experiment, that only the quasilinear structure satisfies all criteria required for a real minimum. Small heat of reaction and the crucial role of entropy in the (HCl)2 formation suggest that the dimer (HCl)2, in contrast to (HF)2, represents a true van der Waals molecule. A very small energy difference between the two stationary points (minimum and saddle point) suggests a very high rate of interconversion between two possible structures of the quasilinear form. Common features of and differences between (HCl)2 and (HF)2 are pointed out.