Microwave Optical Double Resonance Spectroscopy of Metal Oxides

Abstract Continuous wave lasers have been employed in gas phase microwave optical double resonance (MODR) experiments. MODR spectroscopy combines the high resolution of microwave spectroscopy with the high sensitivity to transient molecules of optical spectroscopy. Detectability of MODR effects under weak (linear) and strong (nonlinear) optical pumping conditions is discussed. Experiments are described in which the 496.5 nm line of an Ar ion laser and a tunable, cw dye laser are used to observe fourteen microwave rotational transitions in the X1Σ (ν = 0,1) and A1Σ (ν = 0‐5) states of 138Ba16O and one transition in the A1Σ (ν = 1) state of 137Ba16O. Partially deperturbed rotational constants for BaO A1Σ are B (ν) = 0.25832(2)‐0.001070(5) (ν + 1/2) cm−1. A description is given of the cw dye laser and of the procedure for tuning the laser to coincide with any desired rotational line of the BaO A1Σ‐X1Σ transition. A wide range of metal oxides, halides and hydrides have been produced under conditions suitable for MODR spectroscopy.