When using a given basis set, both energy and this quantity are multiplied by a dimensionless scaling factor usually close to 1 to account for a term called ZPVE. For a transition state, this quantity takes on an imaginary value since it corresponds to a negative eigenvalue of the mass-weighted Hessian of a Born-Oppenheimer surface. Olfactory receptors identify molecules by their value for this quantity, according to the controversial (*) "swipe card model." Heavy isotopologues have lowered values of this quantity, lowering the rate constant in the kinetic isotope (-5[1])effect. For a covalent bond modeled as a Hookean spring, this quantity is (read slowly) one over two pi times the square root of force constant over reduced mass. For 10 points, name this quantity that describes (10[1])the rate at which an atom in a molecule oscillates, measured in (10[1])hertz. ■END■