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 JKa,Kc=201,19-192,17 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 (N2) and oxygen (O2) broadening coefficients are measured here for the first time. Values of the pressure broadening coefficients, γ(N2)=4.03±0.06MHz/Torr and γ(O2)=2.49±0.04MHz/Torr are obtained at room temperature, with statistical 3σ uncertainties given. The value for air broadening is then derived to be γ(air)=3.71±0.09MHz/Torr, where the uncertainty includes possible systematic errors.