Measurement of the pressure broadening coefficient of the 625 GHz transition of H2O2 in the sub-millimeter-wave region

The hydrogen peroxide (H2O2) molecule plays an important role in stratospheric ozone chemistry as a reservoir molecule in the HOX cycle. The Superconducting Sub-Millimeter-Wave Limb Emission Sounder (SMILES) instrument in the Japanese Experiment Module (JEM) on the International Space Station monitors H2O2 using the pure rotational J(Ka,Kc) = 20(1.19)-19(2.17) transition at 625.044 GHz in the ground vibronic state. Accurate retrievals of H2O2 abundances rely on a knowledge of pressure broadening effects for this transition, and the required nitrogen (N-2) and oxygen (O-2) broadening coefficients are measured here for the first time. Values of the pressure broadening coefficients, gamma(N-2) = 4.03 +/- 0.06 MHz/Torr and gamma(O-2) = 2.49 +/- 0.04 MHz/Torr are obtained at room temperature, with statistical 3 sigma uncertainties given. The value for air broadening is then derived to be gamma(air)= 3.71 +/- 0.09 MHz/Torr, where the uncertainty includes possible systematic errors. (C) 2009 Elsevier Ltd. All rights reserved.