Microwave-infrared double resonance spectroscopy of an OCS molecule insidea He-4 droplet

The dynamical behavior of single OCS molecules embedded in large (N-4=6000) superfluid He-4 droplets has been investigated with high resolution double resonance infrared-microwave spectroscopy. The individual lines for the ro tational transitions 2 <---->1, 3 <---->2, 4 <---->3, and 5 <---->4 are cle arly resolved in the difference double resonance spectra and reveal a fine structure. This is especially well resolved for the 3 <---->2 transition wh ich exhibits five separate lines having widths of about 50 MHz and separate d by 200 MHz. The possible origin of the splitting is discussed. (C) 2000 A merican Institute of Physics. [S0021-9606(00)00228-2].