Knowledge Bank

The $\nu 4$ and $\nu 2$ fundamental bands of $SiH4$ are being studied coincidences with the $CO2$ and $N2O$ laser lines. By observing passive Q-switching caused by the $SiH4$ gas being placed in the laser cavity, 25 near coincidences have been detected. These near coincidences have been studied by the technique of ``Stark Lamb dips”. Although $SiH4$ is a non-polar molecule in its equilibrium structure, the energy levels belonging to the E species of the tetrahedral molecular symmetry group exhibit first order Stark shifts due to rotation- or vibration-induced dipole moments. Since the induced moments are very small, the Stark shift is observable only by the Lamb dip technique. Three such Stark patterns have been observed and two of them enabled us to study the Stark shifts of $SiH4$ in detail. From an analysis of the parallel and the perpendicular Stark patterns and an experiment using a second laser for frequency measurement, the rotation-induced dipole moment and vibration-induced dipole moment have been determined. Further search for coincidences and Stark Lamb dips is in progress using a $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}CO2$ laser.