DETECTION OF AMBIENT NO BY LASER-INDUCED PHOTOACOUSTIC SPECTROMETRY USING A(2)SIGMA(-X(2)PI (0,0) TRANSITIONS NEAR 226 NM())

Trace concentrations of NO are detected under ambient conditions by la ser-induced photoacoustic spectroscopy. NO is excited via its A(2) Sig ma(+)-X(2) Pi (0,0) band with radiation near 226 nm, and the subsequen t heat released is monitored by a microphone. Rotationally resolved ph otoacoustic spectra are recorded and fit with the use of a multiparame ter computer simulation based on a Boltzmann distribution. Transition probabilities and rotational energies are used as input parameters. Th e effect of buffer gas pressure, buffer gas, laser energy, and NO conc entration on the PA signal is investigated both experimentally and by model calculations. Limits of detection (LODs) of 1.2, 2.8, and 4.9 pp m are obtained for NO in Ar, N-2, 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 d esign. The results are compared with those of previous studies using c omplementary laser-based spectroscopic techniques.