Knowledge Bank

Low-J rotational levels in the $V4-2$ vibrational level of the $H2COA~\pm A2$ state are excited by a Nd:YAG pumped frequency-doubled dye laser. An electric field is applied in a direction perpendicular to the linear laser polarization. Quantum beats are observed between $|M|$ and $|M\pm 2|$ levels originating from the same $Jka,Kc$ asymmetry component. The electric field is varied over the interval 1 to 5kv/cm and quantum beats in the 4-40 MHz range are observed with an accuracy of $\pm 0.02$ MHz. The dependence of the measured Stark coefficient on J and $Ka$ is a probe of Coriolis perturbations within the $A~$ state and Interactions between the prepared $A~$ level and the ""lumpy continuum"" of the $X~$ state.