Circa conservation of vibrational energy among three strongly coupled modes of a cyanine dye molecule studied by quantum-beat spectroscopy with a 7Â fs laser

The four modes can be classified into two triplets: G1(ωa, ωb, ωc) and G2 (ωb, ωc, ωd), which satisfying a circa sum-frequency reaction ω1 + ω2 ≅ ω3, G2 satisfies the circa-conservation of instantaneous energy due to the symmetry of vibrational modes, while the G1 does not.