The imaginary frequency due to the reaction vector in a
transition state calculation must not be included in the
thermochemical calculation. The number of genuine vibrations
considered can be:
3N-5 for a linear ground state system, 3N-6 for a
non-linear ground state system, or 3N-6 for a linear
transition-state complex, 3N-7 for a non-linear
transition-state complex.

This keyword must be used in conjunction with THERMO if
a transition state is being calculated.