Detection of Ambient NO by Laser-Induced Photoacoustic Spectrometry Using A2Σ+ − X2Π (0,0) Transitions Near 226 nm

Abstract

Trace concentrations of NO are detected under ambient conditions by laser-induced photoacoustic spectroscopy. NO is excited via its A2Σ+-X2π (0,0) band with radiation near 226 nm, and the subsequent heat released is monitored by a microphone. Rotationally resolved photoacoustic spectra are recorded and fit with the use of a multiparameter computer simulation based on a Boltzmann distribution. Transition probabilities and rotational energies are used as input parameters. The effect of buffer gas pressure, buffer gas, laser energy, and NO concentration on the PA signal is investigated both experimentally and by model calculations. Limits of detection (LODs) of 1.2, 2.8, and 4.9 ppm are obtained for NO in Ar, N2, and air, respectively. The ultimate sensitivity of this approach is greater with LODs projected in the low-ppb range by utilizing higher laser energies and an improved system design. The results are compared with those of previous studies using complementary laser-based spectroscopic techniques.