Observation of second-order Stark effects in silane, SiH4

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Abstract
The Stark effect on rovibrational transitions of the tetrahedral molecule silane has been studied by laser Stark spectroscopy, i.e., by applying dc fields of up to 65 kV/cm and monitoring the absorption of fixed frequency ir laser lines. The coincidences observed occur between the ν4 fundamental of SiH4 and N2O laser lines. Using the inverse Lamb dip technique single M components of three high J transitions could be resolved, and two of these have been identified by rf–ir double resonance. In both cases the Stark shift is due to the second‐order Stark mixing of A1 with A2 rotational levels. The analysis of the Stark effects is consistent with the ground state centrifugal distortion moment ϑzxy=3.34×10−5 D measured previously by Kagann, Ozier, and Gerry. Experiments to measure the frequency offset Δν=νM−νL of the molecular absorption lines from the nearest laser line have also been performed, using the beat between two N2O lasers. Direct evidence of the second‐order Stark shift has been obtained by observing Stark Lamb dips with a continuously tuned laser.