The molecular bonds of diatomic molecules can be modeled as
springs. The spring constant, k, for a HCl molecule is known to be 480 N/m. If the
reduced mass of the molecule is 1.626×10-27 kg, what is the frequency at which the
atoms in this molecule vibrate?
2 pi f = sqrt(k/m)
for m you can use that reduced mass or just use the mass of a hydrogen atom which is about 1 gram/mol or .001 kg /6*10^23 atoms = (1/6)*10^-26 = 1.66 *10^-27 kg because the H is the part that moves because the Cl is 35.5 times as massive which is what that "reduced mass" is about.
thank you!posted by Brad