A possibility of stabilization in an external homogeneous electric field on the HeH, (2 'A') metastable state relative to its nonadiabatic decay into the 1 ' A' state is investigated theoretically. If the lowest vibrational levels of the HeH, (2 'A') state might be stabilized, one would try to detect the radiative transition 1 'A' e= 2 'A' from these levels and thus to verify experimentally the existence of the HeH2(2'A') state. It is shown that the separation between the potential energy surfaces (PESs) of the states in question and the energy of their avoided crossing point do increase in the field. Moreover, it is shown that in the fields with strength up to lo7 V/cm the nonadiabatic decay of the 2 ' A' state along one of the vibrational modes may be closed. However, along two other modes such decay still may occur. It is noted nevertheless that the question of such stabilization possibility in inhomogeneous fields (i.e., in ionic crystal or on its surface) is still open. The effect of the field was taken into account within an analytic two-level model. The unperturbed PESs were calculated by the CASSCF method. 0 1996 John Wiley & Sons, Inc. an active interest in this problem, but the attempts of Schaefer et al. [3] and Romelt et al. [4, 51 to locate a minimum point on the potential energy surface (PES) of the HeH, excited singlet state for C,, and C,, structures failed. In 1983 Farantos et al. [6] found such a minimum point in the case of C, structure and showed that the HeH, (2'A') state in this structure was bound by almost 1.5 eV relative to the He + H 2 ( B ' C:) asymptote and a barrier preventing this state formation from the asymptote was 0.24 eV. It was also shown [6] that