High-sensitivity infrared-microwave-microwave triple-resonance spectroscopy of isomerizing molecules

We describe a molecular-beam infrared-microwave-microwave triple-resonance spectroscopy technique for measuring the rotational spectrum of single quan tum states in energy regions where isomerization occurs. Infrared-microwave (IR-MW) saturation spectroscopy, with a resolution of 300 KHz, has been em ployed for the excitation of single eigenstates. In a second step, the rota tional spectrum of the prepared quantum state is measured using a technique based on the Autler-Townes splitting of states. The technique is illustrat ed by measurements of the rotational spectrum of single quantum stales of 4 -chlorobut-1-yne near 3330 cm(-1). (C) 2001 Published by Elsevier Science B .V.