At present, element 112 (E112, eka-mercury) can be unambiguously 
identified only by its chemical properties due to the contradictory 
nuclear-physical experimental data. Chemical experiments on E112 are currently 
under way at FLNR (Dubna, Russia); similar work is in progress at 
GSI (Darmstadt, Germany) and PSI (Villigen, Switzerland). It also involves 
an attempt to confirm the synthesis of E114 and E116 (being their decay product, 
E112 should be detectable in these experiments). Superheavy element properties 
are very difficult to study experimentally, because only single atoms 
are available. In this connection, theoretical predictions of their properties 
based on accurate ab initio calculations are highly desirable. Because of 
the strong relativistic contraction and stabilization of the 7s orbital, 
E112 in its closed shell ground state configuration 7s2 6d10 was expected 
to behave like a rare gas than like Hg. As a first step in the extensive 
study of E112 chemistry, bonding in simple diatomic molecules is modeled. 

Our first results of relativistic correlation calculation of spectroscopic 
properties for the ground states of the E112H, E112H+, E1122 and E112Au 
molecules are reported and compared with those of the corresponding compounds 
of its lighter homologue Hg. The methods of generalized relativistic 
effective core potential, fully relativistic Fock-space coupled clusters with 
single and double cluster amplitudes (RCCSD), scalar relativistic UCCSD(T) 
and spin-orbit direct configuration interaction are used to ensure high 
accuracy. The primary importance of the proper account for the spin-orbit 
interactions in E112 compound calculations have been demonstrated. 
The most dramatic impact of spin-orbit effects was observed for E112H. 
The calculated equilibrium distance, Re=1.662 A, in E112H is notably 
smaller than Re=1.738 A in HgH, whereas the E112H dissociation energy 
is at least as large as in HgH. These data are quite different from the 
values previously obtained within the scalar-relativistic Douglas-Kroll 
approximation for E112H [Nakajima and Hirao, Chem. Phys. Lett. 329, 511 (2000)], 
Re=1.829 A and very small De (0.06 eV). Although the contribution of the 
spin-orbit interaction for the E112Au and E1122 molecules is smaller than 
for E112H, it still significantly affects the calculated spectroscopic 
parameters and, therefore, it should not be neglected in reliable calculations. 
Our results indicate that the ground-state monovalent E112 compounds resemble 
the Hg ones whereas no similarity between the behaviour of E112 and inert gases 
was found. 

The present work is supported by the RFBR (grants No. 06-03-33060 and 06-03-32346).