Abstract: The new finite groups called C^* and D^*, which correspond to C_∞υ. and D_∞h pointgroups, respectively, are introduced. The significant advantage of C^* and D^*is theirsimplicity and completeness to classify molecular orbitals for all of linear molecules. Groupsymmetry orbitals (SMO) and character Slater determinants(CD) of linear molecules based upon C^* and D^*groups are definited and discussed. Apreliminary singly and doubly excitedcharacter configuration (CD-CISD) program is developed, and the pilot calculations about thesimple linear molecules are performed and compared with that by the programGAUSSIAN94. The calculation results proved that the CD-CISDis a high effective calculation methodfor linear molecules.

Key words: Group symmetry orbital (SMO), Character determinants (CD), Linear molecule, Symmetry adaptation, SMO-CDCI method