Triatomic radicals

We shall divide the triatomic radicals thus far studied into three groups dihydrides, monohydrides, and nonhydrides. 

The spectra of a number of triatomic radicals with 15 valence electrons are now known for elements of the first period they are B02, N3, and NCO. In addition, the isoelectronic ions C02+ and N20+ have been investigated. The spectrum of B02 was observed by Johns41 in the flash photolysis of a mixture of BCI3 and 02, but later was found to be identical to the green bands observed in most flames and arcs containing boron.42 Isotope shifts (B1X-B10) and alternate missing lines in the spectrum immediately identify the carrier as... 

The preceding review shows that the number of triatomic radicals for which ultraviolet spectra have been observed and analyzed during the past 15 years is quite considerable. Some of these radicals were long known to chemists, but others, like C3, CNC, NCN, and B02, had not previously been assumed to exist in chemical reactions. In addition, in several instances, particularly in the case of CH2, the importance of both low-lying singlet and triplet states has been established. In this way, even apart from the determinations of the structures of the radical, the spectroscopic studies have advanced the understanding of the chemistry of free radicals. 

VI-14. Triatomic Radicals Photochemical Production, Detection, <6 Reactivities 261... 

The experimentally observable effects of the linear relativistic Renner coupling are perturbations in the vibronic spectra of 11 states. Since zero-order energy levels which differ by one quantum of the bending mode, the effects are maximal for o). These perturbations have previously been observed in the Renner spectra of triatomic radicals, such as NCO, NCS and GeCH [40-42] and have been termed Sears resonances [42]. Another signature of the linear relativistic vibronic coupling is intensity transfer to vibronic levels with an odd number of quanta of the bending mode [43,44]. 

If we consider the decomposition reactions of these substances as double exchanges it becomes clear that the so-called radicals are exchanged for an equivalent amount of, for instance, hydrogen. In the action of methyl cyanide on potassium hydroxide solution, for example, the triatomic radical- 2113 takes the place of three atoms of hydrogen of which one belonged to the potassium hydroxide, and two to water. In the decomposition of urea, the diatomic radical 0-takes the place of two atoms of hydrogen that belonged to two molecules of potassium hydroxide ... 

Triatomic Radicals Group 6 (also monatomic) GnH2n-i... 

The isolation and study of triatomic radical anions is also a matter of considerable interest. The ozonide ion has been successfully studied as alkali metal salts in an argon matrix (74) and the S3 ion as a substitutional species in a sodium chloride crystal as host 69,75). The latter species has also been identified by resonance Raman studies as the one responsible for the blue colour of ultramarine blue and lapis lazuli (70). Sulphur also forms deep blue solutions under certain circumstances in many other media (e.g. hexamethylphosphoramide and dimethylformamide), and it is unquestionably the S3 ion which is the species responsible for the colour in these cases also. 

To summarize, in sodium azide there is experimental and theoretical evidence to associate the 730-nm optical absorption with an F center. The association of colloidal particles with the 520 nm band produced by irradiation and subsequent heating is plausible. An F2 center and a bent triatomic radical have been offered to account for the 610-nm absorption band. The Fj center is less tenable because one would not expect an infrared absorption to be associated... 

The bent triatomic radical as a possible model is less than definitive because the assumptions in the analysis are arbitrary. It should be shown that no other molecular radical predicts the shift of the 1721 cm absorption in the isotopically labeled NaNa. Clearly, further theoretical and experimental work is needed before the defect giving rise to the 610 nm band is definitively assigned. Table I contains a summary of irradiation-produced bands in NaNa. 

Table A-8. Enthalpies of Formation of Triatomic Radicals at 1 atm an.l 0"K in the Ideal Gas State, 377...

The spectrophotometric method has been extended to certain triatomic radicals some of the other methods available for the detection of atoms and diatomic radicals are diflicult to apply to large radicals. 

Kinetic studies on two triatomic radicals (NCV and NF ) have been carried out, and the band spectrum of N has been observed in discharge-flow systems. The sources of these radicals were the reactions... 

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