Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

334 DETECTION AND ESTIMATION OF INTERMEDIATESSolid state spectra are, in general, broader than the corresponding gas-phasespectra, and there may be some frequency shift of the various spectroscopicfeatures. Thus some care must be exercised before absorptions in the solid phaseare ascribed to particular species on the basis of gas-phase identifications. Furthercomplications introduced by the matrix include splittings and changes in oscillatorstrength of optical transitions, but these effects may not themselves interferewith correct identification of the absorbing species. The nature of thematrix shifts is not understood, although some empirical data has been collected.McCarty and Robinson305 examined the matrix shifts in different matrices of the3P1-'S0 resonance line of atomic mercury, and this work has been extended byBrewer et aL306. Meyer3" finds that the absorption features of atomic sodiumor potassium in argon, krypton or xenon matrices are shifted to the blue, andthat there are signs of a triplet structure. If the matrix sample be warmed up, theabsorptions broaden and shift to the red. Barger and Broida308n309 have madesimilar studies of radical species in the region 3000-4500 A. A Knudsen cell wasused to produce a molecular beam of known density of C, C2 and C,. In the case308of C3 trapped in Ar, Kr, Xe, O,, N,, CO, and SF6 matrices it was found that theline widths of the 'n, t 'El transition varied from 40 to 500 cm-', while theline shifts were in the range 410 to 1065 cm-' (all positive, except with a carbondioxide matrix, in which a red shift was observed). There was no definite effect oftemperature, nor did there appear to be any great effect of the matrix on intensities.Experiments309 on the species C, were less successful, and identifications werepossible only for the species trapped in carbon dioxide. With this matrix, 5 bandsof the A34 t X3n, (Swan) system, and 4 bands of the forbidden A3nU t X'Z;system were observed.The blue solid prepared by trapping the pyrolysis (or electric discharge) productsof HN, has been mentioned already, and the solid was one of the lirstsubjects of infrared matrix isolation study. Dows et d310 were able to ascribe mostof the infrared absorption features of the solid to HN,, NH,N, and NH,, andfrom the behaviour of the spectrum on warming the solid up from 90"K, theywere able to show that further absorption bands were associated with the species(NH),(x > 2 and may be 4). During the warming up process, di-imide, N2H2,appears, and the presence of imidogen, NH, at 90" K was inferred. Milligan andJacox3" obtained the infrared absorption of NH and DH by the photolysis ofHN3 and DN, in Ar, N, and CO matrices at 4" K, 14" K and 20" K. It wasshown that an appreciable concentration of NH was present in the ground, 'Z-,state, and from the reactivity observed in the CO matrix it was inferred that aside reaction is the appearance of H atoms by rupture of the H-N bond in HN3.Identification of NH and N,H, in the photolysis of HN,-N, matrices at 20" Khas been made unequivocal by studying the effect of substitution in HN, of H byD and 14N by 15N in the different positions312. Both cis- and trans-forms of N2H2were observed. NH appears as well as NH2 in the vacuum ultraviolet photolysis3'