Driving rotational transitions in molecules on a chip.

Polar molecules in selected quantum states can be guided, decelerated, and trapped using electric fields created by microstructured electrodes on a chip. Herein we explore how transitions between two of these quantum states can be induced while the molecules are on the chip. We use CO (a(3) Π(1) , v=0) molecules, prepared in the J=1 rotational level, and induce the J=2←J=1 rotational transition with narrow-band sub-THz (mm-wave) radiation. First, the mm-wave source is characterized using CO molecules in a freely propagating molecular beam, and both Rabi cycling and rapid adiabatic passage are examined. Then we demonstrate that the mm-wave radiation can be coupled to CO molecules that are less than 50 µm above the chip. Finally, CO molecules are guided in the J=1 level to the center of the chip where they are pumped to the J=2 level, recaptured, and guided off the chip.

Beam action spectroscopy via inelastic scattering.

In this article, a new technique we call Beam Action Spectroscopy via Inelastic Scattering (BASIS) is demonstrated. BASIS takes advantage of the sensitivity of rotational state distributions in a supersonic molecular beam to inelastic scattering within the beam. We exploit BASIS to achieve increased sensitivity in two very different types of experiments. In the first, the UV photodissociation spectrum of OClO is recovered by monitoring intensity changes in the pure rotational transition of a spectator molecule (OCS) downstream from the nozzle, revealing a new vibrational structure in the region between 30,000 and 36,000 cm(-1). In the second, the mid-IR vibrational spectrum of acetylene is recorded simply by monitoring a single pure rotational transition of OCS co-expanded with acetylene. The technique may prove particularly fruitful when an excitation process produces product dark states that are not easily probed by conventional spectroscopy.