Abstract The vibrational frequencies and corresponding normal mode assignments of thiocyanogen are examined theoretically using the Gaussian03 set of quantum chemistry codes. All normal modes were successfully assigned to one of six types of motion (C N stretch, C–S stretch, S–S stretch, S–C N bend, C–S–S bend, C–S–S–C torsion) utilizing the C 2 symmetry of the molecule. Molecular orbitals and bonding are examined.