Elemental iodine (I2) reacts with ozone (03) in the gas phase to form a solid iodine oxide with the stoichiometric composition I4O9. The reaction was studied in a flow system, with a N2/02 mixture as carrier gas, at a total pressure of 100 kPa and in the temperature range 293-370 K. It was shown by gas-phase titration that 3.9 ± 0.2 molecules of 03 were consumed per I2 molecule reacted. The reaction rate fitted a rate law that was first order in 03 and in I2. The rate constant, k = (-d[I2]/di)/([I2] [03]), in the range 293-370 K and in units of dm^mor'-s"1 2, was given by In k = (14.7 ± 0.6) -(2050 ± 230) r1.

The spin-orbit relaxation of Hg(6,P1) to yield Hg(6,P0) was investigated in the presence of various gases. The quantum yields of Hg(6,P0) formation (defined as relaxation to Hg(63Po)/total relaxation) in the presence ofCO, CO,, NH,, ND,, H,O, D,O, C2H6, C(CH,),, C3H,, 2,2-C3H6D2, C3D,, n-C4H,, and i-C4Hlo were: 0.88 + 0.07, <0.01, 1.05 + 0.05, 1.00 k0.08, 0.76 + 0.18, 1.06+ 0.26, 0.64 k0.16, 0.56 40.10, 0.58 +0.02, 0.14+0.01, 0.51 k0.07, 0.47+0.10, 0.11 k0.01, and 0.05+0.01, respectively. The extent of the spin-rbit relaxation process appears to be related in an inverse manner to the availability and accessibility of channels leading to the formation of Hg(6'S0), rather than to the fulfillment of electronic-vibrational resonance conditions. This in turn suggests the existence of Hg(63Pl)--quencher intermediates having lifetimes long enough to permit several vibrations.La relaxation spin-rbitale de Hg(6,P1) pour donner Hg(6,P0) a tte etudike en presence de nombreux gaz. Les rendements quantiques de la formation de H~(~, P , ) (definis par relaxation de H~(~, P , ) sur relaxation totale) en presence de CO, CO,, NH,, ND,, H,O, D,O, C,H6, c-C,H6, C(CH,),, C3H8, 2,2-C3H6D,, C3D8, n-C4Hlo et i-C4Hlo sont: 0.88 + 0.07, 10.01, 1.05 + 0.05, 1.00 + 0.08, 0.76 + 0.18, 1.06 + 0.26, 0.64 + 0.16, 0.56+0.10, 0.58+0.02, 0.14+0.01, 0.51 k0.07, 0.47+0.10, 0.11 k0.01 et 0.05+0.01. Le domaine du procCd6 de relaxation spin orbitale apparait comme ttant en sens inverse de la disponibilite et de I'accessibilitC des canaux menant a la formation de Hg(6'S0) plutBt que du remplissage des conditions de resonance electronique-vibrationnelle. Ceci suggkre I'existence d'intermtdiaires de pitgeage Hg(6,P,) qui ont des temps de vie assez longs pour permettre plusieurs vibrations.Canadian Journal of Chemistry, 50, 176 (1972) In a recent communication from this laboratory (1) we have presented preliminary data on the spin-orbit relaxation of Hg(63Pl) atoms to yield Hg(63Po) in the presence of various gases. Because of the importance of these measurements in the elucidation of the energy transfer process in mercury photosensitization (2-9) and the controversial nature of the problem (10-14), we have investigated the spin-orbit relaxation process in greater detail and extended our measurements to more molecules. Particular attention was focused on molecules such as CO, CO,, H,O, D,O, NH, and ND,, that have been previously considered ( 2 4 , 10, 15) from the point of view of the resonance theory of spin-orbit relaxation,The relative increase of the total ~g ( 6~~, ) quenchingcross section with the relative decrease of the energy discrepancy, AE, of the electronic and the vibrational transition, were cited as basis for the resonance theory. However, there were only few direct measurements such as rate constants for the occurrence of reaction 1. The result of Scheer and Fine (10) for CO has recently been questioned (14, 126).Also, of particular interest were the alkanes which have been thoroughly studied in the past and were shown to exhibit a num...

An investigation of the H g ( 6 3 P l t C 0 system by physical measurements (emission, pressure studies) relevant to the reported Hg*CO species have yielded no additional evidence of its formation.Chemical experiments on the decomposition of ethylene and H z are in accord with formation of a long lived (> s) species. The relative quenching rate constants of the species by CzH4, Hz, and C O are 1:0.10-0.18:0.023, respectively.The reliability of the "carbon monoxide effect" as a criterion for distinguishing the nature of the quenching process is discussed in the light of a CO enhancement effect (-30%) observed in the Hg (63Pl) photosensitized decomposition OF hydrogen in the presence of CO and at conditions of incomplete quenching. An alternative to Hg*CO excimer formation is also discussed. This approach is based on the possible formation of Hg(63Po) atoms in quantities in excess of those currently accepted, when Hg-CO mixtures are irradiated with 2537 Pi light.

The Raman spectrum of 1409, formed by the gas-phase reaction of Iz with 03, has been measured. Freshly prepared samples of 140, gave broad band spectra characteristic of an amorphous solid. Vibration bands at 780, 740, 620 and 450 cm-' were observed. It was established conclusively that 1409 is a distinct molecular species and not a mixture of I,Os and Iz04.

The quenching of Hg(63P1), Hg(63P0), and Hg(61P1) by the alkanes was investigated by a theoretical model based on the formation of a relatively long-lived (Hg*HR) complex on a potential energy surface, most likely a polar one, which leads to the quenching of Hg* primarily by C–HHg bond rupture. The decomposition of the (Hg*HR) complex via C–HHg bond scission was treated as a unimolecular decomposition. The potential-energy surfaces associated with the reaction coordinate were defined by thermochemical and spectroscopic data, semiempirical calculations and, whenever not critical, by reasonable estimates. The unimolecular decomposition rate constants were calculated making use of the Rice–Ramsperger–Kassel–Marcus (RRKM) theory. This approach correlates the nature and magnitude of the C–H vs C–D isotope effects and the large variation in quenching efficiencies of the various alkanes satisfactorily with the C–HHg bond strength, zero point energy, and structural effects (vibrational degrees of freedom). Consequently, both the relative increase of the quenching cross section and the relative diminution of the effect of C–H bond strength with increasing excitation energy of the mercury atom is accounted for in terms of the relative increase in the active energies of the (Hg*HR) molecule and its activated complex.