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Photo-Oxidation of Iodomethane in Solid Argon'

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Photo-Oxidation of Iodomethane in Solid Argon' Photo-oxidation of Iodomethane in Solid Argon' J. F. OGILVIE,~VIRGINIA R. SALARES,AND MICHAELJ. NEWLANDS Deportment of Chemistty, Metnorial Universio of Ne,vfo~rndland,St. John's, Newfo~rndlattdAIC 5S7 Received June 14. 19733 J. F. OGILVIE,VIRGINIA R. SALARES,and MICHAELJ. NEWLANDS.Can. J. Chem. 53,269 (1975). Photolysis of iodomethane in the presence of oxygen in solid argon near 10 K has yielded several products detected by their vibrational absorption spectra. Isotopic labeling of reactants has proved methanal, water, hydrogen iodide, carbon monoxide, carbon dioxide, and hydro- peroxyl radicals to be significant products, and a further set of major absorptions is attributed to hydrogen hypoiodite H01, hydrogen-bonded to methanal. Other minor vibrational features are discussed, and a possible reaction scheme is briefly outlined. J. F. OGILVIE,VIRGINIA R. SALARESet MICHAELJ. NEWLANDS.Can. J. Chem. 53,269 (1975). La photolyse de I'iodomCthane, en presence d'oxygkne dans I'argon solide pres de 10 K, con- duit a plusieurs produits detectes par leur spectre d'absorption vibrationnelle. Le marquage isoto- pique des reactifs a prouve que le mtthanal, I'eau, I'iodure d'hydrogkne, le monoxyde de carbone, le dioxyde de carbone et des radicaux hypropkroxyles sont des produits importants; on a attribue un autre groupe majeur d'absorptions B de I'hypoiodite d'hydrogkne (HOI) lie par pont hydrogkne au mCthanal. On discute d'autres vibrations mineures et on dCcrit un schema rtactionnel possible. [Traduit par le journal] Introduction of each experiment, after deposition of gases during 5-10 h, frozen samples were irradiated for 10-30 h In his investigation of photolysis of iodo- (low pressure Hg lamp) and 1-2 h (HPK 125 lamp); the methane in solid oxygen Roebber (I) postulated extent of photodecomposition of reactants and formation that several trapped radicals may have been of products was measured by analysis of vibrational produced, but lack of isotopically substituted absorption spectra recorded before and after each reactants and problems of spectral range and irradiation operation. Flow of gases to the refrigerator For personal use only. was controlled by needle valves in the range 0.14.7 ~mol resolution hampered positive identification. s-', monitored by Penning and Pirani pressure gauges. Also only a few trapped radicals were at that The gases were frozen on a Csl window in the refrigerator, time characterized by vibrational spectra; even held at 8-10 K (measured by a Chrome1 us. 0.07% Fe/Au for many pertinent stable substances, reliable thermocouple). The irradiation sources were mercury arcs: Philips HPK 125, 125 W operating at a pressure absorption spectra were available for neither -8 x lo5 N m-2, or a specially constructed lamp, 8 W gas phase nor argon matrix. Now that these operating at a pressure of 1.3 x lo3 N m-2 so as to conditions no longer prevail, we are able, in emit principally at 39 412 and 54 069 cm-'. A filter performing similar experiments, to identify transmitting 8 000-14 000 and 24 00047 000 cm-I was occasionally used with the HPK 125 lamp. Spectral slit several products unambiguously, and we have widths of the spectrometer varied from 0.3-1.5 cm-' also obtained evidence for a previously un- in the range 200-4000 cm-'; wavenumber accuracy and detected molecule which seems to be a major reproducibility were 0.5 cm-' for sharp lines. product. Iodomethane (H312CI from Fisher, D312CI from Merck, Sharp and Dohme, and H313CI (86.3% enrich- Experimental ment) from Prochem) was distilled and degassed before The apparatus consisted essentially of a refrigerator use. 1602was generated from KMn04; I8O2 (94 atomic% Can. J. Chem. Downloaded from www.nrcresearchpress.com by Simon Fraser University on 06/20/17 (Air Products Displex CS-202) mounted in an infrared enrichment) was obtained from Yeda. Mixtures OF spectrophotometer (Perkin-Elmer 225) and connected 1602, 1802, and L60180(-40 atomic% 180 randomly to both a metal high-vacuum pumping system and a distributed, as deduced from ozone byproduct composi- glass manifold for sample preparation. In the conduct tion) were prepared by electric discharge of 1602 and 1802. Argon (Matheson, 99.998% nominal purity) was used directlv from the cvlinder. D712C0 was 'Presented at XI International Symposium on Free generated from p~l~oxymethyle~e-d2(~erck, Sharp Radicals, Berchtesgaden-Konigssee, September, 1973. and Dohme). Mixtures of iodomethane vapor (or 'To whom correspondence should be addressed. D212CO) and argon, or oxygen and argon, were pre- 3Revision received September 20, 1974. pared and stored several hours before use. CAN. J. CHEM. VOL. 53, 1975 WAVENUMBER, cm-I FIG. 1. Selected portions of spectra of H313CI:1602:Ar= 1 :25:200. Upper spectrum, before photolysis; lower trace, sample had been irradiated for 27 h with the low-pressure Hg lamp. * represents background feature. For personal use only. CO,, D3CI FIG.2. Selected portions of the spectrum of D312CI:L602:Ar= 1:20:100. Upper spectrum, before photolysis; lower spectrum, sample had been irradiated for 30 h with the low-pressure Hg lamp and 2 h with the HPK 125 lamp. Results By comparison of relative intensities during Representative spectra recorded before and various photolytic operations within particular after irradiation of iodomethane-oxygen-argon and between different experiments, lines ex- mixtures are shown in Fig. 1 and 2. That a hibiting similar intensity patterns were grouped Can. J. Chem. Downloaded from www.nrcresearchpress.com by Simon Fraser University on 06/20/17 reaction had occurred after irradiation was and are now presented in text and tables. Isotopic clearly evident from the reduction in intensity labeling of reactants permitted identification of iodomethane lines and appearance of many of produced substances; mixtures of both 12C- new absorptions. (In contrast, when only and 13C-containing iodomethane or all of iodomethane-argon mixtures were irradiated, 1602,1802, and 160180were particularly useful no spectral changes were detected.) Character- in indicating the number of either carbon or istic growth patterns with the two radiation oxygen atoms in carriers of major absorption sources were observed for the new absorptions. features. By this method, it was ascertained OGILVIE ET AL.: PHOTO-OXIDATION OF IODOMETHANE TABLE1. Absorption lines (cm-I) of water molecules produced after irradiation of specified reactants* H~"CI H312CI H~I~CI D312CI D3I2CI 1602 l80, 1602 I6O2 lSO2 3723.5 3710 3723.5 2756 2742.5 3712.7 3700.4 3714 2733 3700 br 3687 br 3696 br 271 8 br 2708 br 3678 br 3678 br 3621 3622 3614 3605 3614.3 2666 2651 2640 1615 br 1615 br 1612 br 1183 br 1177 br 1594.5 1595 1591 1578.6 1591 1176 1585 1585 'In this and following tables, br = broad and sh = shoulder. TABLE2. Absorption lines (cm-I) of methanal molecules produced after irradiation of specified reactants, with reference lines H3IZCI H~~~COH~I~CI H~I~CI D~~~CID~~~CO D312CI 1602 (ref. 5) 1602 I6O2 (ref. 6) 180, For personal use only. that no carrier of other than weak absorptions ments indicated dissimilar rates of iodomethane contained two or more carbon or oxygen atoms. decomposition and methanal formation during Varying mole fractions of iodomethane and irradiation. Simultaneous destruction of oxygen by dilution with argon was also helpful, methanal by radiation from the HPK 125 lamp a technique which Roebber (1) did not exploit. was confirmed in separate experiments with Water, characterized by absorptions listed in D2C0: 0, :Ar samples. Table 1, had both sharp lines at wavenumbers Carbon monoxide and dioxide were both attributed to isolated molecules (2-4), and broad easily detected; wavenumbers are listed in lines attributed to water hydrogen-bonded to Table 3. Atmospheric carbon dioxide hampered other polar molecules within the same cavity quantitative absorbance measurements in the bounded by argon and oxygen molecules. 2350 and 667 cm-I regions, but there is no During an annealing operation, in which the doubt that rates of carbon dioxide formation sample temperature was allowed to rise to and of iodomethane decomposition were dis- Can. J. Chem. Downloaded from www.nrcresearchpress.com by Simon Fraser University on 06/20/17 20-30 K before recooling, sharp lines at 3712.7 similar. In fact, use of the HPK 125 lamp and 3723.5 cm-' decreased in intensity, lines after the low-pressure lamp resulted in a rela- at 3678 and 3614 cm-' increased, and that at tively .rapid increase of CO,. This behavior is 3700 cm-' was little affected. consistent with its production via a secondary Methanal is also readily identified by its process. characteristic fundamentals, for which wave- Carbon monoxide lines are generally as numbers are listed in Table 2 and compared previously reported (7-lo), with slight variation with published values (5, 6). Intensity measure- attributed to matrix environment effects. An CAN. J. CHEM. VOL. 53, 1975 FIG.3. Absorptions between 2050-2200 cm-' produced by photolysis of: (a) HSL2CI:1602 : Ar = 1 :25: 100; (b) H312CI:'s02:Ar= 1:13:110; (c) H313CI:L602:Ar= 1:25:200. TABLE3. Absorption lines (cm-') of carbon oxide molecules produced after irradiation of specified reactants - -- - For personal use only. 'Overlapped with CL802initially present in lB02sample. ?Obscured by DICI line. *Obscured by D2CL80absorption. TABLE4. Absorption lines (cm-I) of hydroperoxyl but another appeared about 1525 cm- l, also radicals produced after irradiation of specified reactants unaffected by "0-labeled reactant. These ob- servations lead to assignment of the absorbing H,lZCI Hgl2CI H313C1 D312CI -. 'Go2 l6O2 l6Oz species as hydrogen iodide (1 1). The breadth of the lines and shift from the gas-phase band 1390 1381 1390.0 center both indicate extensive hydrogen bonding. 1388 1379.2 1388.3 Weak absorptions at wavenumbers noted in 1100 1039.5 1100.5 1022 Table 4 indicate by their behavior on isotopic labeling that the carrier is the hydroperoxyl intense line at 2149 cm-' has been previously radical, consistent with similar wavenumbers measured in different experiments on this Can.
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