Ed Grant (experiment) John Hepburn (experiment) Roman Krems (theory)
Kirk Madison (experiment) Takamasa Momose (experiment) Moshe Shapiro (theory)
Ruth Signorell (experiment)

Ed Grant, John Hepburn, Ruth Signorell and Takamasa Momose collaborate on the development of techniques of REMPI and ZEKE molecular photofragment spectroscopy to study dynamics of molecules, ions and plasmas at subKelvin temperatures. Many interesting phenomena should exist even at the moderately low temperatures of 10 K - 1 mK. For example, a significant enhancement of reaction cross sections is expected for some systems below 10 K due to the increase of efficiency of the tunneling process and resonance effects. Chemical reactions at low temperatures are relevant to interstellar chemistry, where molecules are produced at temperatures around 10 K. However, due to the great experimental challenges, reliable data on chemical reactivity below 100 K are scarce. The proposed methods of making free cold molecules below 0.1 K will be powerful techniques for the study of molecules at moderately low temperatures and a crucial starting point to reach ultra-cold temperatures with a wide variety of molecular species.

The study of ultracold chemistry will take us into a strange new world, in which even the smallest activation energy exceeds the available thermal energy. At such low temperatures, the large de Broglie wavelength entirely changes the nature of reaction dynamics and even collisions of large molecules exhibit significant quantum effects. Energy barriers on the potential energy surface play a different role because quantum tunneling becomes the dominant reaction pathway. Since tunneling and resonances are characteristic of this regime, they can serve as ultra-sensitive probes of particular features of the potential energy surface. Chemical reactions have been predicted to be very efficient in the limit of zero temperature; however, no measurements of ultracold chemical reactions have been reported to date. Our experiments will thus be pioneering the field of ultracold chemistry. Interactions of molecules at low temperatures can be tuned by DC electromagnetic fields and this degree of control may lead to the development of ultracold controlled chemistry. By shifting molecular energy levels with external magnetic or electric fields, one can bring an excited bound level of the reactive complex into or out of resonance with the collision energy leading to enhancement or suppression of the reaction efficiency. Moreover, external fields can mix states so that forbidden electronic transitions become allowed and the reaction rate may be controlled by the field strength. External fields may also influence kinetic properties of ultracold molecular gases such as diffusion. We will study these and other mechanisms for external field control of molecular dynamics both theoretically (using numerical simulations) and experimentally. Ours will be the first study of DC field effects on ultracold chemical reactions.