Page 10 - Visions of the Future Chemistry and Life Science

1

Laser snapshots of molecular motions

Gareth Roberts
Department of Chemistry, University of Cambridge, Lensfield Road,
Cambridge CB2 1EW, UK

1.1 Introduction

The molecular motions that drive the conversion of energy and matter in
physics, chemistry and biology take place over an amazingly rapid time,
measured in millionths of a billionth of a second (a femtosecond (fs)). On
time scales of this duration, atoms and molecules come together, exchange
energy and transfer atoms in the very act of transforming one material into
another. To map out such processes as they happen necessitates the appli-
cation of laser pulses with durations of tens, or at most hundreds, of fem-
toseconds to take ‘snapshots’ of the changes in real time.
This chapter discusses the application of femtosecond lasers to the
study of the dynamics of molecular motion, and attempts to portray how
a synergic combination of theory and experiment enables the interaction
of matter with extremely short bursts of light, and the ultrafast processes
that subsequently occur, to be understood in terms of fundamental
quantum theory. This is illustrated through consideration of a hierarchy of
laser-induced events in molecules in the gas phase and in clusters. A spec-
ulative conclusion forecasts developments in new laser techniques, high-
lighting how the exploitation of ever shorter laser pulses would permit the
study and possible manipulation of the nuclear and electronic dynamics in
molecules.

1