Spectroscopic Study of Atmospheric Trace Gases

Abstract

Molecular spectroscopy offers the tools and instrumentation needed to unveil the structure and characteristics of molecules that are found within planetary atmospheres. In order to do this we examine the frequencies of light that these molecules either absorb or emit. It is the fine structure of these absorption or emission features that give us information about their physical state.. In our lab we use a near-infrared source to probe various molecules and examine absorption features and their dependency on both temperature and pressure. In this study we plan to retrieve the N2-broadened widths, pressure-induces N2-shifts and N2-broadened line mixing coefficients for twenty two transitions in the P branch of the ν1+ν3 band of acetylene mixed with nitrogen. The gas mixture has been selected to be 10% acetylene and 90 % nitrogen. We will record spectra using a 3 channel tuneable diode laser spectrometer. The system contains a temperature controlled single pass absorption gas cell of fixed length, a room temperature cell filled with pure acetylene gas used to create a reference spectra and a third background cell. The system is controlled by LabVIEW software which will be discussed.Simulations have been performed on the v1+v3 band using data obtained from the HITRAN database and will be presented. . From the simulations we determined that we can measure twenty two lines in the P-branch of this band. These lines are all within the interval of P(1)-P(31). For each line we will record spectra at pressures of 100, 250, 400 and 500 torr and for each pressure we plan on measuring 7 different temperatures ranging from -60 to 60C. From these recorded spectra we hope to obtain line parameters using a nonlinear least squares fitting routine. The routine will allow for use of several different line shape models. This study will be the first one over a range of temperatures.