Sensitivity and mass selectivity of NO detection by stepwise photoionization

Abstract

State selective stepwise laser photoionization of nitric oxide molecules has been investigated using mass spectroscopic detection with a quadrupole filter. The ionization was carried out in two steps, the first being excitation with a tunable dye laser in the (A ²∑⁺,v′=0.1 state at wavelength around 226 nm and 215 nm, and the second being excitation beyond the ionization limit with a fixed frequency laser at 266 nm, i.e. the fourth harmonic of a Nd:YAG laser. The sensitivity of NO detection and the mass resolution of this method has been studied. The ion signal of NO⁺ was observed with linear pressure dependence at partial densities of NO down to 1×10⁵ cm⁻³. This corresponds to a density per state of about 2.5×10⁴ cm⁻³. The mass selectivity was investigated at the various isotopic components of natural nitric oxide¹⁴N¹⁶O,¹⁵N¹⁶O,¹⁴N¹⁸O and the isobare¹⁴N¹⁷O.