  It is shown that the slope of the repulsive part of the interaction potential
between hydrogen atoms above the dissociation limit decreases with decreasing
internuclear separation. Such a form of the repulsive potential explains the
reduction of the shock and quasi-isentropic compression curve slopes of
hydrogen isotopes at megabar pressures obtained in recent experiments [R. F.
Trunin, V. D. Urlin, and A. B. Medvedev, Phys.-Usp. \textbf{53}, 577 (2010), R.
I. Ilkaev, \textit{et al.}, AIP Conf. Proc. \textbf{706}, 73 (2004)].
