Vibrational Spectra of Diatomic Molecules

The lowest vibrational transitions of diatomic molecules approximate the quantum harmonic oscillator and can be used to imply the bond force constants for small oscillations.

The following is a sampling of transition frequencies from the n=0 to n=1 vibrational level for diatomic molecules and the calculated force constants. Molecule Frequency x1013 Hz Force constant N/m HF 12.4* 970 HCl 8.66 480 HBr 7.68 384 HI 6.69 294 CO 6.42 1860 NO 5.63 1550 * From vibrational transition 4138.52 cm-1 in Herzberg's tabulation.

These bond force constants were calculated from the vibrational frequency in the same way the force constant for HCl was calculated.