The fifth-order contribution to the oscillations in photon echoes of anharmonic vibrators

Vibrational photon echo experiments on the C=O stretching mode of carbon monoxide bound to hemoglobin revealed pronounced oscillations with a beat frequency which corresponds to the anharmonicity of the vibrator. Intensity-dependent measurements show that the oscillatory signal is due to interference between the third- and fifth-order polarization. Such oscillations cannot occur in the third-order signal unless the inhomogeneous width exceeds the anharmonicity. An expression is derived which simultaneously describes the intensity dependence, the phase, and the damping of such oscillatory signals. (C) 1999 Elsevier Science B.V. All rights reserved.