Knowledge Bank

Stark-Induced Quantum Beat Spectroscopy is used to measure dipole moments in the $\nu 4$ vibrational levels of the first excited singlet state in formaldehyde-$h2$ and -$d2$. The polarization of the incident laser pulse is perpendicular to the direction of a 0 to 5 kV/cm static electric field. Evolution of the coherent superposition produced between Stark-split M-sublevels of a selected $A1A2$ rotation-vibration level exhibits a quantum interference effect which is observable in the undispersed fluorescence. Analysis of these oscillations yields dipole moments with a precision in excess of 1 part per 1000. The results can be interpreted in terms of $S1\sim S0$ perturbations and vibronic coupling models.