The rates of reactions of ClzP atoms with methane, and with a series of substituted methanes, have been measured using mass spectrometric analysis of molecular reactant consumption in the presence of excess Cl atoms, with pseudo first order kinetic analysis ; this approach minimizes secondary reactions and the problem of reaction stoichionietries. The following rate constants were obtained for CI + RH reactions : l~g~~( k c~~/ c m~ molecule-' s-I) = (-10.294+0.043)-(778k 16) KIT, 300-686 K ; l o g l o ( k~~s~i / c m 3 molecule-' s-l) = (-9.673 k 0.087) -(776 & 30) K / T , 300-604 K ; l~g~~( k c~~~i~/ c m~ molecule-' s-I) = (-10.078 k0.074)-(629& 26) K / T , 298-621 K ; l~g~~( k c~~~~/ c m~ molecule-' s-I) = (-10.480+0.051)-(599k 19) KIT, 297-652 K ; l~g~~( k c~~c i~/ c m~ moIecuIe-' s-I) = -12.64+ 0.08, 652 K. The correlations of these results with data from competitive chlorination studies are discussed in relation to the uncertainty surrounding the Arrhenius parameters for the primary reference reaction, Values for the kinetic isotope (H/D) rate constant ratios, (~C H J~C D~) and ( k c~c i~ /~C D C I~) , were C1+ HZ+HCl+ H. measured over wide ranges of temperature : loglo(kCHs/kCD4) = (-0.155f0.024)+(384+ 12) K / T , 298-1018 K ; 298-1006 K. lOglo(kCHCl~/kCDC13) = (-0.014+0.020)+(167If:9) K / T , These results are in agreement with the predictions of the semi-empirical BEBO (bond-energy-bond order) method.Chlorination reactions with molecules RH, involving abstraction of an H atom, and leading to formation of HCl and a radical R, constitute one of the largest series of elementary reactions for which relative (although not absolute) rate constants have been measured. These kinetic data have provided some of the most extensive results for the testing of theories of absolute reaction rates, including kinetic isotope effects. Examples include the reactions : Cl+H,, D2, HT l * ; Cl+ CH4, CD4, CzH6, CzD6.2 However, surprisingly few direct measurements of absolute values for rate constants are a~ailable.~ All the reactions in the series C1+CH4, CH,Cl, CH2C12, CHC13, have activation energies less than 20 kJ f110l-l,~ whilst the values for -AU,",, in these exothermic reactions gradually increase in this series from about 4 kJ mol-l for Cl+ CH4, to about 42 kJ mol-1 for C1+ CHC13.4 Measurements of the ratios of rate constants (ICR*H/ICR"H) for reactions of this type have been carried out using competitive methods, with C1 atoms generated either thermally or photolytically from C12 : kWH Cl + R'H+R' + HCI, C1+ R"H+R" + HCl. 1547 7kRttn9

Values of the spectroscopic constants for the B3rI(O+) -X'Z+ systems of IF, IC1 and IBr have been evaluated and used to determine the RKR turning points for the B311(O+) and X'C+ states of the iodine monohalides. The RKR potential functions have been used to calculate r-centroids and Franck-Condon factors for the B-X systems.

The spectrum of the thermal emission of NO2 at about 1200°K was found to be similar to that of the N O + 0 3 chemiluminescence. It is concluded that these spectra are transitions from similar low-lying vibrational levels of the same excited electronic state of NO2 to the ground state. The 0 +NO chemiluminescence and NO2 fluorescence excited by Hg 4358 A radiation involve transi-

The kinetics of overall combination and light emission (due to excited HNO) in the reaction of H with NO are closely similar to the kinetics of the combination of 0 with NO and its associated " air after-glow " chemiluminescence. Both reactions were studied by measurement of the intensities of their respective light emissions in a fast flow system at 1-2 mm Hg total pressure. Preliminary work has been extended and shows that in both O f N O and H+NO reactions there is a significant dependence of emission intensity and combination rate upon the nature of the carrier gas used as third body. Negative temperature coefficients for both the O+NO and H+NO emission intensities were observed, and the dissociation energy of the ground state €€NO molecule was thus determined as 48.6 kcal/mole.

Direct determinations of the rate constants kl and kz (cm3 molecule-I s-l) are reported, for the reactions of H 'S atoms with NO2 and 03, using atomic resonance fluorescence in a discharge-flow system to detect hydrogen atoms. Measurements of kl for reaction (1) at four temperatures from 298 to 653 K were made : H+NOZ+NO+OH; (1 ) ki the following overall Arrhenius expression was obtained : Measurements of kz for reaction (2) were made at three temperatures between 298 and 638 K : 10glokl = (-9.3191f: 0.084)-(174f 31)/T (20). kz H+Oj + OZ+OH. These results gave the expression : log1 okz = (-10.005 & 0.102)-(224 f 26)/T (20).