INTRODUCTION

The earth’s atmosphere is composed of gas phase molecules, and these molecules affect climate and life on the planet by absorbing light from the sun.  A few examples are described below.

When ordinary oxygen molecules (O2) absorb UV light from the sun, they split into atomic oxygen (O).  These highly reactive oxygen atoms then readily react with surrounding O2 molecules to form ozone (O3).  Ozone in the stratosphere very efficiently absorbs harmful UV rays from the sun that would otherwise damage or kill life on the surface of earth.  (In 1995, Crutzen, Molina, and Rowland received the Nobel prize in chemistry for their work on ozone and their discovery that chlorofluorocarbons (freon) released by spray cans were destroying the protective ozone layer.  Worldwide concern over loss of the earth’s protective ozone layer (the ozone hole) eventually led to restrictions on the use of CFCs.) 

On the other hand, ozone in the lower parts of the atmosphere (the troposphere) is a major component of smog and can damage life.  This ozone is produced by NO2, which in turn is produced from NO that is produced during the combustion of fossil fuels (e.g., in an automobile engine).  A key step in this reaction is the absorption of sunlight by NO2. 

Another byproduct of combustion is CO2, which is called a greenhouse gas because it absorbs light from the sun and efficiently converts it to heat, which raises the temperature of the planet. 

Spectroscopy is one of the main ways that people study gas phase molecules and the interaction between these molecules and light.  However, when gas phase molecules absorb visible or UV light from the sun, the resulting spectra are usually highly congested and disorganized.  As a result, the spectra are often difficult and sometimes impossible to interpret. 

Our research group is exploring the development and use of coherent 2D spectroscopy to address severe congestion and disorganization normally observed in the electronic (UV-visible) spectroscopy of gas phase molecules. 

Funded by the NSF (Award #0616661)