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It has been predicted by theoretical models that ethane and ethanol are present in icy mantles covering dust particles in dense interstellar clouds. Laboratory spectra of ethanol embedded in astrophysically relevant ice matrices were compared to the Infrared Space Observatory and ground-based astronomical spectra of high mass protostars. From this comparison strict upper-limits of ethanol (compared to solid water) on interstellar grains could be derived that are below 1.2%. In dense star forming regions ethanol is observed in gas phase with an abundance which is many orders of magnitude in excess of predictions based on pure gas-phase chemistry. Ethane has not been observed in the interstellar gas or on grains. In contrast, ethane has been detected in several comets with a percentage of

Dimethyl ether (DME, CH 3 OCH 3 ) is one of the largest organic molecules detected in the interstellar gas and shows high abundances in star-forming regions, known as hot molecular cores. The observed DME might be formed on grains or by secondary gas phase reactions from a precursor molecule, which in turn was sublimed into the gas phase from the grain surface. Studies on the stability and degradation pathways of DME therefore provide important constraints on the evolutionary cycle of large organic molecules and chemical pathways in the interstellar medium. We studied the UV photodestruction rate of DME in a solid argon matrix. DME was destroyed with a half-life of 54 seconds under laboratory conditions, which corresponds to 8.3 × 10 5 years in a dense cloud. We discuss the UV photochemistry of DME in the context of two issues: its formation mechanism and its chemistry in hot cores. Chemical models of shielded hot core regions indicate that UV photodestruction is relatively unimportant for DME, even by the internally-generated radiation field. These models clearly show that gas phase processes are almost certainly responsible for the formation of interstellar DME.

UNLABELLED: The present research reports on a survey of 96 subjects between the ages of 60 and 95 years, living close to Paris in a social collective habitat. The aim was to show, using goodness-of-fit statistical tests (P < 0.1), how old people lifestyles can subject them to generated chemical or bacteriological indoor pollutants. Risk factors due to lifestyles were analyzed in relation to complaints and to health condition. There are many ways that old people are exposed to pollutants: difficulty in maintaining the residence, preference for staying in the kitchens, substantial use of cleaning chemicals. However, the principal risk for health problems is arguably inadequate ventilation (unclean screens, blocked air vents, etc.), which increases the concentration of indoor pollutants. These risks are amplified by ignorance about the hazards of inadequate ventilation. PRACTICAL IMPLICATIONS: The present investigation suggests that the lifestyle and the behavior of old people could be the cause of an interior air pollution of their housing. Measures realized in representative dwellings selected in relation to results must confirm that these risks would require the installation of an automatic monitoring system of the indoor air near these people.

We use Fourier transform infrared (FTIR) reflection spectroscopy (incidence angle of 5°) to characterize thin films of ethylene oxide (EO) and water/EO mixtures (between 11 and 170 K under a pressure of 10 −7 mbar). The photochemistry of EO in matrices, in the solid phase and ice was also investigated at 11 K using a microwave excited hydrogen flow lamp. Solid EO has two solid phases: an amorphous phase which is obtained below 75 K and a crystalline phase observed below 110 K. EO begins to sublimate around 100 K with a binding energy of 20 ± 2 kJ mol −1 . Gaseous mixtures of EO containing water traces deposited at 30 K lead to the condensation of small clusters (EO 2 ) m (H 2 O) n . The vibrational spectrum of EO diluted in water ice remains nearly unchanged between 11 and 120 K. Between 120 and 130 K, a large part of EO is released and changes in the frequencies and in the profile of the EO absorptions are observed. In the water lattice the trapped EO is hydrogen-bonded to water molecules below 120 K. In the range 130–160 K, EO is primarily present as clathrate hydrate. UV photochemistry of EO showed to be rather independent on the matrix or solid it is embedded. In matrices, in the solid phase and in ice, three primary photoproducts are formed from two different channels: acetaldehyde, methane and carbon monoxide. Only in matrices, acetaldhehyde decomposes partially into ketene and into a acetylene/water complex.

Dimethyl-ether has been identified in the interstellar gas in cold molecular clouds. It is therefore most probable that it can be trapped in the mantles of low temperature interstellar grains. Laboratory studies have been performed in order to simulate the photo-dissociation of dimethyl-ether trapped in ice at 10 K using vacuum ultraviolet radiation. Primary photo-products have been identified as formaldehyde and methane. They are both produced through two channels without subsequent reactions with water ice. We discuss the infrared spectroscopic measurements of dimethyl-ether and the mechanisms involved in the photo-dissociation of this organic molecule.

This paper focuses on systematic examination of the vibrational frequency shifts of some molecules trapped in water ices. It is shown that for the bands, for which the laboratory taken data are available, the magnitude and the sign of a vibrational shift for the molecules trapped in water ice can be approximately predicted using empirical correlations with macroscopic properties of the host. These results can be useful for identification of the carriers of absorption in matrix spectroscopy, for the study of intermolecular interactions, for a number of applications involving remote spectroscopic sensing of molecular species in the atmosphere and in space.

FTIR spectra of solid ClNO 2 in interaction or not with amorphous water ice between 11 and 200 K were analyzed, and the photochemistry of these solids was investigated. When ClNO 2 is deposited on an ice surface at 30 K or trapped in the water lattice, no ionization or reaction with water is observed even after annealing from 30 to 180 K. Photolysis of thin ClNO 2 films at 266 nm produced dinitrogen tetra-oxide as primary product. When ClNO 2 is trapped in ice, exposure to ultraviolet light quantitatively converted ClNO 2 to nitric acid hydrates.

Fourier Transform Infrared Spectroscopy (FTIR), is used to characterize thin films of sulfur dioxide trapped in excess of amorphous water ice and to study the photo-oxidation of pure solid SO2 or of SO2 diluted in water ice. These laboratory experiments were undertaken in an attempt to find information on the formation of hydrated sulfuric acid detected on Europa's surface. Vibrational spectra at 30 K of mixed films containing SO2 with an excess of water depend on the deposition conditions. A metastable (SO2)m(H2O)n phase and a solid solution of SO2 in water ice have been evidenced. Irradiation at 266 nm of mixed films SO2/O3/H2O produces sulfur trioxide and hydrogen peroxide without traces of sulfuric acid. Irradiation of films of pure SO2, under 200 nm, leads to sulfur trioxide and to ozone. When SO2 is diluted in amorphous water ice, new weak bands that appear after irradiation suggest the formation of sulfuric acid. PACS No.: 82.50Hp

Fourier Transform infrared reflection spectroscopy (incidence angle of 5°) was used to characterize thin films of sulfur dioxide and thin films containing water and sulfur dioxide in various ratios between 10 and 200 K under a pressure of 10 −7 mbar. Pure solid sulfur dioxide begins to sublimate above 108 K with an sublimation enthalpy of 29±3 kJ mol −1 .When sulfur dioxide is deposited on a water ice surface or trapped in the ice bulk, no reaction is observed even after annealing. Gaseous mixtures of sulfur dioxide containing water traces deposited at 30 K leads to condensation of pure sulfur dioxide and small clusters (SO 2 ) x (H 2 O) y . States of mixed H 2 O/SO 2 films with excess of water are dependent upon deposition conditions. With He as carrier gas, a metastable (H 2 O) m (SO 2 ) n phase is observed. Deposition without carrier gas leads to a solid solution of dioxide sulfur in water ice. Above 120 K a large part of sulfur dioxide diluted in water ice escapes, and one observes changes in the frequency and the profile of sulfur dioxide absorptions which probe the gradual transformation of water ice. Sulfur dioxide which remains in the lattice escapes at 170 K when water ice sublimates.

Fourier transform infrared reflection spectroscopy (incidence angle of 5°) was used to characterize thin films of dimethyl ether (DME) and of mixtures containing water and DME between 10 and 160 K under a pressure of 10 −7 mbar. Solid DME has two solid phases: an amorphous phase which is obtained below 65 K and a crystalline phase >65 K. From 90 K, DME begins to sublimate with surface binding energy of 20±2 kJ mol −1 . Vibrational spectrum of DME trapped in water ice remains nearly unchanged from 30 to 120 K. Between 120 and 130 K, a large part of DME is released and strong changes in the frequencies and the profile of the absorptions of DME are observed. This behavior suggests the formation of clathrate hydrate. Below 120 K, the trapped DME is hydrogen-bonded to water molecules.

Detailed infrared spectroscopic studies of the photo-dissociation at 266 nm of ClNO2 trapped in argon matrices with subsequent experiments conducted with a xenon lamp at λ>360 nm are reported. Formation of cis and trans ClONO in equilibrium with ClNO2 is observed after irradiation at 266 nm. At λ>360 nm the transformation of trans ClONO into cis ClONO occurs. On prolonged photolysis at 266 nm, ClONO dissociates into ClON and O ( 1 D ) atom and into ClO+NO as evidenced in reactive matrices (solid oxygen and nitrogen).

Infrared spectroscopy has been coupled with the matrix isolation technique. First, to identify the ozone dimer isolated in solid argon, and second, to investigate the mechanism of its photodissociation at 11 K using the 266 nm laser line. Identification of dimers, which are trapped in two different sites, was performed through the observation of the ν3 asymmetric stretching modes. By absorption of one photon, dimers are photodissociated with a high photolysis rate when compared with that of ozone monomers, suggesting the absence of cage recombination of the photofragments. Experimental observations suggest that the major pathway after photolysis is the formation of an excited transient species O4*, which fragments into O+O3. A two-step mechanism, involving the subsequent reaction of O(1D) with O3 formed in a first step appears unlikely.

Recent results about the ozone photochemistry in solid matrices (O 2 , Ar, N 2 ) and water ices are reported. Several areas are reviewed: photochemistry in the visible and UV of ozone monomer, photochemistry of ozone involved in weak complexes, reactivity of atomic oxygen with various partners in nearest neighbour. Although reactions occurring in matrices are not the same as in gas phase, pathways displayed in matrices can bring information for gas phase modelling.

Fourier Transform infrared reflexion spectroscopy (incidence angle of 5°) was used to characterize thin water ice films between 10 and 160 K under a pressure of 10−7 mbar. Spectral features of the OH stretching band related to structural differences are described and discussed in the light of this and previous works performed either by infrared transmission or by reflection absorption infrared spectroscopy (RAIRS) at large incidence. Comparison of our spectra with those obtained in the literature shows that assignment of the bands is still uncertain based on our current understanding of the physical nature of water in the solid phase.

The interaction of ozone with ice films under high vacuum was studied with single reflection Fourier transform infrared spectroscopy (incidence angle of 5°). Both amorphous and crystalline ice were...

The mechanism of photooxidation of sulfur dioxide in the presence of ozone and under irradiation at 266 nm has been investigated at low temperature in an argon matrix. Formation of stable SO3 occurs from the reaction between SO2 and O(1D) and also by oxygen atom transfer within the SO2:O3 complex. Use of isotopic SO2 species led to unusual observations suggesting that photooxidation of SO2 proceeds via an intermediate species, namely, OSOO; this trioxide sulfur isomer transforms into SO3 by tunneling. In the gas phase, the quenching of the O(1D) atom by SO2 could occur through this intermediate.

The photodissociation of ozone trapped at high dilution in solid argon has been reinvestigated at different temperatures and various photon flux, combining irradiation at 266 nm and infrared spectroscopy. In argon, recombination of O+O2 is a major pathway and the weak decrease of ozone is due to cage exit of oxygen atoms which is dependent of the temperature and of the initial photon flux. Kinetic curves are well fitted by a double exponential expression and a model based upon two different cage exit pathways is proposed.

Co-deposition of argon or nitrogen dilute samples of natural and isotopic carbon monoxide and halogen molecules (Cl2, Br2, BrCl) produced new narrow absorptions lines assigned to X2···CO complexes. With BrCl, in an argon matrix two 1:1 complexes were observed, one stronger than the Br2···CO complex, the other one weaker than the Cl2···CO complex. In the nitrogen matrix, one complex was only observed, namely, the ClBr···CO complex. For all complexes, observed shifts were larger in nitrogen than in argon matrices and similar to available gas-phase results for Cl2···CO and Br2···CO complexes. Irradiation of the samples with a filtered xenon lamp (λ > 360 nm) induced in an argon matrix (not in a nitrogen matrix) the isomerization of the complexes into a metastable form CO···X2 identified for the first time. Back isomerization was observed by weak temperature increase. The structure and energetics of the four complexes formed between CO and BrCl were investigated by DFT ab initio calculations and compared to c...

Infrared spectroscopic studies have been conducted on the products of the reaction between atomic oxygen in its ground and excited states with normal and isotopically substituted methyl chloride in argon matrixes at 11 K. With the O(1D) atom, the major product is the hydrogen-bonded complex between formaldehyde and hydrogen chloride. Abstraction of a hydrogen atom from CH3Cl by O(1D) appears as a minor channel. Small amounts of HClCO were also found. Formation of CO−HCl as a secondary and primary product was observed. Reaction of CH3Cl with the O(3P) atom was evidenced. Spectra suggest the formation of a collision complex CH3Cl···O formed by addition of an oxygen atom to CH3Cl. Ab initio calculations about the structure and vibrational spectrum of the CH3ClO singlet and CH3Cl···O triplet are reported.

Natural and isotopic nitrosyl chloride (ClNO) isolated in nitrogen or argon matrices were irradiated with light at 266 nm. Weak absorption lines observed after photolysis were assigned to nitrogen hypochlorite (ClON). Spontaneous conversion of ClON into ClNO was observed and kinetic studies were consistent with a tunneling mechanism. Calculations using DFT and CCSD(T) were made for all isotopic species of each isomer. Energies, structures, harmonic vibrational wavelengths were calculated. Photoisomerization of ClNO into ClON as well as that of FNO into FON was also discussed.

The matrix isolated infrared spectra of complexes formed by trans and cis HONO (DONO) isomers with hydrogen chloride have been obtained in nitrogen at low temperatures by the irradiation of the nitrosylchloride complex with water. Ab initio calculations were carried out to investigate the energy surface of the bimolecular complex. Four stable structures of trans HONO:HCl complex and three stable structures of cis HONO:HCl complex were found and characterized by their equilibrium geometries, vibrational frequencies and stability study. Comparison of the calculated frequency shifts with the experimental data allowed to give the most probable structure of the cis and trans HONO:HCl complexes.

The photochemistry of ozone trapped in solid nitrogen and mixed matrices has been reinvestigated using irradiation at 266 nm and infrared spectroscopy between 10 and 25 K. In this temperature range the most probable reaction channel appears to be the formation of metastable excited nitrous oxide molecules that fragment mostly into an oxygen atom and nitrogen. Recombination of O+O2 is negligible, suggesting that the atomic oxygen that is formed from the deactivation of excited N2O is bound to the nitrogen molecule, preventing the reformation of O3 and leading to a fast first-order photodecomposition of ozone in highly diluted samples. The experimental value of the photokinetic constant suggests that the photodissociation cross section of ozone in matrices at 266 nm is weaker than that measured in the gas phase.

The photodissociation of 18 O 3 (fully substituted ozone or 888) in the visible region has been studied in a natural oxygen matrix at 10 K combining 693 nm laser irradiation with infrared absorption spectroscopy. Ozone 888 is converted to the (unsymmetrical and symmetrical) 668 and 686 species which are further converted to the normal 666 species through the exchange of 18 O with 16 O atoms. The overall photodissociation of 888 is a first-order process and a reasonably simple model is proposed which reproduces satisfactorily the observed kinetic results. The value of the photolytic kinetic rate constant suggests an increase in the absorption cross section for the visible band with respect to that measured in the gas phase. The experiments suggest an enhanced formation rate of the unsymmetrical 668 species with respect to the symmetrical species 686 during the 18 O oxygen atom recombination with the matrix 16 O 2 molecules.

The hydrogen-bonded complexes between C2H4 and HNO3, and their deuterated analogs, have been isolated and characterized in argon matrices. The concentration studies, matrix annealing, and UV irradiation effects prove formation of stable 1/1 π-electron hydrogen-bonded complexes isolated in two trapping sites. Eight perturbed HNO3 vibrations and three perturbed C2H4 vibrations were identified for this complex. The spectra also indicate the existence of a less stable 1/1 π-electron hydrogen-bonded complex for which one perturbed frequency due to the OH stretching mode was identified. Photochemistry of the complexes was also studied with the 266 nm laser line and with a medium-pressure mercury lamp. The photolysis products of HNO3, OH and NO2 radicals, recombine in the matrix cage to form nitric acid, and peroxynitrous acid which are the main reaction products. The new major product of photolysis of the C2H4−HNO3 complex is ethylene glycol nitrite formed in double-addition reaction of OH and NO2 radicals to t...

Complexes of ozone with chlorine, bromine and bromine chloride were reinvestigated in argon matrix by Fourier Transform Infrared spectroscopy. All three ozone submolecule fundamentals were observed and ν 1 was enhanced in intensity relative to ν 3 . The asymmetric mixed isotopic ozone complexes exhibit a split ν 3 band which indicates unequivalent terminal oxygens. Photolysis of the O 3 /BrCl system which was studied with the 870, 633 and 532 nm laser lines gives only ClBrO as a primary product indicating that the most stable complex between BrCl and O 3 occurs through bonding of ozone with Br. Results show that at 633 nm, ClBrO transforms it into BrClO whereas at 870 nm, it is isomerized to BrOCl. Ab initio calculations undertaken on the structures of O 3 :Cl 2 and O 3 :BrCl support experimental observations.

The vibrational spectrum of N 2 O diluted in a nitrogen matrix is compared to the spectrum of N 2 O produced after the photolysis of ozone diluted in solid nitrogen. The small shift observed between the two spectra is due to the formation of a 1−1 complex between nitrous oxide and molecular oxygen. Upon increasing the temperature, the complex formed after the photolysis of ozone in nitrogen reacts with an oxygen atom leading to O 3 and N 2 O. Analysis of the results brings new information on oxygen atom diffusion in cryogenic solids. As predicted by theoretical investigations, the long-range diffusion of atomic oxygen in a nearly perfect matrix is negligible between 20 and 30 K. However, a fast motion of O( 3 P) at short range, independent of the matrix morphology, is experimentally suggested between 15 and 20 K.

The vibrational spectrum of 2,2,2-trichloroethanol was reinvestigated in argon and nitrogen matrices. No experimental data were found to justify the existence of several conformers. The observed splitting probably arises from alternative trapping sites in the matrix. This conclusion was supported by ab initio conformational studies at the self-consistent field Hartree-Fock, the second order Moller-Plesset and the Becke-Lee-Yang Parr density functional levels of calculation. Only one stable conformation was found, in which CCl3 and CH2O are staggered and OH is in a gauche position, almost parallel to one CCl bond.

Fourier Transform Infrared (FTIR) spectra of the covalent dinitrogen pentoxide molecule isolated in a solid argon matrix at 10 K are reported. The measured frequencies in the 200–4000 cm−1 region are in close agreement with gas phase values previously reported. An accurate and sophisticated ab initio study showed that the stable equilibrium structure, C2 symmetry, was in agreement with the structure previously determined by electron diffraction data.

Matrices formed by the cocondensation of 1,1,1-trichloroethane and ozone in argon were irradiated at 11 K with the laser line at 266 nm. The CH 3 CCl 3 molecule was not photodecomposed at this wavelength. The product identification was made by Fourier transform infrared spectroscopy. Acetylchloride, 2,2,2-trichloroethanol and 1,1-dichloroethylene were observed in the beginning of the reaction. Trichloroethanol is the main product. It is probably formed by insertion of an O atom in a CH bond to give an excited intermediate which may release its excess energy by relaxation in the matrix or by elimination of HOCl, leading to CH 2 CCl 2 . The formation of small amounts of acetylchloride is probably due to direct oxygen attack on the carbon atom. Photolysis of CH 3 COCl and CH 2 CCl 2 was observed upon prolonged irradation between 800 and 250 nm and produced ketene and chloroacetylene, respectively. Fourier transform infrared spectra of CH 3 COCl and CD 3 COCl isolated in argon matrix were also recorded in this work.

Vibrational spectra of16O/17O/18O enriched ozone have been recorded both in argon and nitrogen matrices using Fourier transform spectroscopy. The fundamental bands ν1, ν2, and ν3as well as the combination band ν1+ ν3have been analyzed from two mixtures with different isotopic abundances. Most of the observed absorption peaks were assigned, and a change in the relative intensities of the three fundamental modes was evidenced for unsymmetrical isotopic species. The present investigation has been undertaken to better understand possible mechanisms of isotopic enhancements observed in the stratosphere.

Fourier Transform infrared spectroscopy has been used to study sulfur dioxide isolated at different concentrations in solid argon. Results obtained for various isotopic species of SO2 are reported and discussed. The most stable (SO2)2 dimer in argon matrix is characterized by one ν3 absorption, and possesses a structure with the transition dipole moments of both subunits parallel or antiparallel one to another. Furthermore high resolution allowed to observe in the S16O18O vibrational region additional splittings leading to the conclusion that the four SO oscillators are not equivalent. A force field calculation on the dimer was performed. A good fit was obtained between calculated and observed ν3 frequencies for all dimer isotopic species. The suggested structure of the dimer in argon (Ci symmetry) which appears very different of that one observed in nitrogen matrix could be more realistic with respect to gas phase because the dynamic coupling between dimers and the lattice vibration are less important in argon than in nitrogen matrix.

Due to their importance in stratosphere, spectroscopic studies of halogenated carbonyls (COF2, COFCl, COCl2) and their complexes with Cl2 are reviewed, including previously unpublished data. In particular, quantitative analysis of νCO Fermi resonance has been made for free and complexed halogenated carbonyls. Ab initio calculations have been undertaken on all these structures. The structure, complexation energy and vibrational analysis at the harmonic approximations have been calculated at the self‐consistent field and Mo/ller–Plesset 2 levels. The calculated frequency shifts are in overall agreement with the experimental data. This result was not obvious owing to the weakness of the complexes.

This article describes the Fourier transform infrared spectra of ozone obtained by photolysis of an oxygen matrix at λ≥245 nm. A complex between ozone and atomic oxygen was identified. Results with isotopic oxygen are consistent with a structure in which the oxygen atom is bonded to the central oxygen atom of ozone. Complex formation does not change the photochemistry of matrix isolated ozone. Investigation of the ozone formation was also performed based on the dissociation of normal and scrambled ozone isolated in oxygen matrix. Formation was found to be of a first order reaction limited by the initial number of reactive species. Results are compared with those in gas phase for which recently, molecular oxygen in highly excited vibrationally states has received attention as a possible source of stratospheric O3 via an autocatalytic process.

The matrix isolation technique has been used to isolate and characterize the complexes two hydrogen halides (HCl and HBr) and the nitric oxide (monomer and cis dimer). Identification of the complexes was performed through the observation of the HX and (NO) x (x=1,2) submolecule stretching modes. Ab initio calculation shows that the most stable structure ClH:NO is linear with a 0.002 A shortening of the NO bond distance and an increase of the HCl bond length with an identical amount. Photochemistry of the identified complexes was also studied. The photoproduct of both NO:HX and (NO) 2 HX complexes is XNO (X=Cl, Br) upon UV irradiation. In the case of the (NO) 2 :HX complex the XNO molecule is complexed to HNO in the matrix cage.

Fourier transform infrared spectroscopy has been used to study sulfur dioxide dimer isolated in nitrogen matrices. The results for various isotopic species of SO 2 are presented and discussed. Both number of absorptions observed in the spectra and their splittings after the isotopic substitution confirm that sulfur dioxide dimer with two non-equivalent subunits is present in solid nitrogren.

The reactions of methane and methanol species with excited atomic oxygen generated by ozone have been examined in low temperature argon matrices. The major product of the CH 4 +O( 1 D) reaction was CH 3 OH, confirming a previous prediction of the intermediary of CH 3 OH to the first product in the gas phase reaction. Insertion of an O atom in a CH or CD bond was found to give a similar result. On the basis of kinetic studies two major pathways were observed for the CH 3 OH+O( 1 D) reaction. The first one led to H 2 O and CH 2 O and the second one to methanediol by insertion of an O atom in a CH bond. H 2 O and CH 2 O arise from an intermediate not isolated. Experiments with oxygen-18 and deuterated methanol suggest either an abstraction of a hydroxyl H atom by O( 1 D) or an insertion of atomic oxygen in the OH bond. A weak complex between methanol and ozone was identified, but it did not play a particular role in the reaction.

The IR spectra of the complexes between dimethylether (DME) and hydrogen iodide in nitrogen matrices were reinvestigated with careful attention to the temperature and IR radiation effects upon the higher aggregates. Irradiation using a broad band IR source was found weakly active leading to a nearly stationary population of the two (DME) 2 H + I − species. Irradiation with CO 2 laser lines induced a conformational interconversion of both aggregates to non-hydrogen-bonded forms. The breaking of the strong hydrogen bond was principally governed by irradiation in the range 2600-1500 cm −1 corresponding to the δ CH 3 region whereas the reverse process was observed by increasing temperature above 27 K under the annealing limit or irradiation below 1100 cm −1 . No accurate evidence was found for the occurrence of photochemical proton transfer between the centrosymmetrical and asymmetrical cations characterizing the two investigated complexes.

The reactions of atomic oxygen with CH 2C l 2 and CH 2 Br 2 trapped in argon matrices have been studied by FTIR spectroscopy. O( 1 D) and O( 3 P) were generated in situ by UV photolysis of co-deposited ozone. Products were identified by employing 18 O and scrambled 18 O/ 16 O ozone as well as deuterated methylene halides. Kinetic studies performed on both CH 2 Cl 2 and CH 2 Br 2 with O( 1 D) under the same experimental conditions allowed the reaction pathways to be determined. With CH 2 Br 2 as parent molecule, three routes were evident leading to (i) CHOBr, (ii) CO...(HBr) 2 , and (iii) CH 2 O

Photolysis of argon samples containing Cl 2 , Br 2 , O 3 with 800-360 nm irradiation produced new absorptions at 940.9-932.7 and 818.9-817.5 cm −1 , which were assigned to the new BrClO and ClBrO species. Formation of these species proceeds through photodissociation of BrCl: O 3 and ClBr: O 3 complexes. Photolysis of ClBrO molecules above 400 nm produced BrCl species.

Fourier transform infrared (FTIR) spectroscopy is used to study the vibrational spectrum of ozone trapped in amorphous ice (a situation observed on icy satellites in the solar system). Evaporation of ozone from ice is investigated from 30 to 150 K under a static pressure of 10⁻⁷ Torr. Condensed and chemisorbed ozone on the surface of micropores is released at a temperature between 40 and 80 K, and ozone in water lattice evaporates starting from 120 K. The release of ozone probes the gradual transformation of water ice. The photochemistry of ozone in excess ice is also investigated using 266 nm laser irradiation. At low temperature, condensation of H₂O/O₃ mixtures leads to ozone trapped in pores and cavities, and H₂O₂ is produced through the hydrogen-bonded complex between ozone and free OH bonds. At higher temperature, when a solid solution of ozone in water is observed, H₂O₂ is formed by the reaction of the excited oxygen atom O(¹D) with the nearest water molecules. Kinetic studies suggest that recombination of the dioxygen molecule with ground-state atomic oxygen O(³P) is a minor channel.