Experiments presented in this contribution demonstrate a heterogeneous source of several chlorine oxides, in particular OClO and ClClO 2 , from ClO radicals passed over water-ice surfaces at low pressures. ClO radicals were generated in a flow system and reaction products were monitored by UV-vis absorption spectroscopy and time-of-flight mass spectrometry using electron-impact and resonance-enhanced multiphoton ionization, respectively. In all experiments an efficient release of OClO into the gas phase was observed upon ice eVaporation. No such gas-phase products directly formed in the initial interaction of ClO with the ice surface were detected. To explain these findings, it is proposed that a ClO‚H 2 O complex is formed in a rapidly established equilibrium between ClO monomers and gas-phase H 2 O. The existence of this complex as well as a surface-enhanced ClO-recombination process is assumed to be responsible for the observed efficient reactive uptake of ClO radicals onto the ice surface. Several possible reaction pathways resulting in the formation of the experimentally observed products are presented. As an alternative pathway, H 2 O-facilitated gas phase disproportionation of ClO yielding hypochlorous and chlorous acid and subsequent deposition on the surface is considered. The observation of OClO evolving from an ice surface previously exposed to ClO radicals, as well as the lack of any symmetric ClOOCl dimer formation in the presence of high water mixing ratios, carries some possible atmospheric implications: First, there is currently a missing source of OClO in the chemically perturbed polar vortex. The ClO + BrO reaction is presently believed to be the only source of OClO in the stratosphere, although several studies show this reaction system to severely underestimate OClO production in this atmospheric subsystem. It is suggested that this experimentally observed heterogeneous source of OClO could carry implications for the total atmospheric OClO budget. Second, the ClO‚H 2 O complex could directly or indirectly affect the ClOOCl formation rate and thus strongly impact homogeneous chlorine chemistry.

In this paper we demonstrate the feasibility of ultra-trace resonance enhanced multiphoton ionization (REMPI) detection employing a small broad-bandwidth solid state laser system. The results reported here are compared with measurements carried out with a conventional excimer pumped dye laser combination. Mass selected broad-bandwidth REMPI spectra for the environmentally relevant nitrogen oxides NO and NO2 are presented. Tunable broad-bandwidth laser radiation with a spectral resolution of > 10 cm(-1) in the wavelength range 560-400 nm was employed for the detection of NO2. For NO detection, the range 230-224 nm was covered. Laser radiation was generated using an optical parametric oscillator pumped by an unseeded Nd:YAG laser. A mobile time-of-flight mass spectrometer equipped with an atmospheric pressure laser ionization source allowed for mass selective parent ion detection at m/z 30 for NO and m/z 46 for NO2. The limit of detection was 10 pptV for NO and 20 pptV for NO2. A selectivity of > 2000 for both compounds with respect to N2O5, organic nitrates and NO2 in the case of NO is reported. An improved laser system currently under construction is expected to provide detection limits below pptv mixing ratios for both nitrogen oxides in a 20 s integration interval.

A simple electric field probe was developed and used to assess the electrical fields produced inside an ion-optical system. When attached to an XYZ translation stage, this induction probe electrometer is capable of spatially mapping the electrical fields generated by a variety of ion-optical arrangements. Measurements of the electrical fields produced by a conventional reflectron consisting of discrete electrodes and monolithic volume and surface conductive polymeric reflectrons are compared. The performance of the system is validated and a correction is introduced to compensate for capacitive coupling between the probe and the electrode system investigated.