Microwave electric-resonance optothermal spectroscopy of (H2O)2

The microwave spectrum of (H2O)2 has been measured between 14 and 110 GHz using a newly developed electric-resonance optothermal spectrometer (EROS) described here. The reported measurements extend previous results on the a-type Ka=0–0 and 1–1 bands for the A±2 , B±2 , and E± rotational-tunneling states and include the first observations of the c-type Ka =1–0 band for the A±2 and B±2 states and the a-type Ka =0–0 band for the A±1 states. For the A±1 states an interconversion tunneling splitting of 22.6 GHz is obtained, compared to the 19.5 GHz value found previously for the Ka =0 A±2 and B±2 states.