Trace detection of ambient brominated compounds by laser-induced photofragmentation/fragment detection spectrometry

Abstract

Studies have been performed to evaluate the analytical capabilities of a novel, one color, laser-induced photofragmentation/fragment detection technique for the detection of ambient brominated compounds. Laser radiation at 260.634 nm is used to both fragment the brominated compounds and excite the characteristic Br atom photofragment via its two-photon 4 p 45 p 4 D 0 3 2 ← 4 p 5 2 P o 3 2 transition. Detection is accomplished by either (2 + 1) resonance-enhanced multiphoton ionization (REMPI), or by laser-induced fluorescence (LIF) or stimulated emission (SE) from the 4 p 45 p 4 D 0 3 2 → 4 p 45 1s 4 P 5 2 , 3 2 transitions at 844 and 751 nm, respectively. The SE signal is coaxial to the laser beam and is approximately two orders of magnitude greater than the LIF signal at 844 nm. Measurements are performed in a photolysis cell at total pressures of 1–760 Torr. For REMPI detection, total (nonselective) ion collection is employed using a miniature pair of electrodes. The absorption cross section of the two-photon 4 p 45 p 4 D° 3 2 ← 4 p 5 2 P 0 3 2 transition is estimated to be 1.8 × 10 −45cm 4s and limits of detection in the ppb are obtained for CH 3Br, CHBr 3, and CHClBr 2.