Equilibrium CAs and CSb bond lengths

The equilibrium structures of some small molecules containing the CAs or the CSb bond are determined using the method of predicate observations. The input data are the semi-experimental equilibrium rotational constants (experimental ground state rotational constants corrected for the rovibrational contribution calculated from the ab initio cubic force field) and the bond lengths and bond angles calculated ab initio using the CCSD(T) method and a relativistic effective core potential of quadruple zeta quality. It is shown that this method, avoiding difficult isotopic substitutions, allows us to obtain reliable equilibrium structures.