Free radicals by mass spectrometry. XL. Primary processes and transient intermediates in the mercury (3P1) photosensitization of hydrazine

The low pressure mercury (3P1) photosensitized decomposition of hydrazine has been studied at 55 °C in a fast flow reactor coupled to a mass spectrometer. Direct evidence was obtained for the participation of N2H2, N2H3, NH2, and NH in the decomposition, and two primary decomposition modes were established[Formula: see text]

Clinical factors determining curative tumor dose

The dominant factor determining treatment policy, when considering radiotherapy of a neoplastic disorder, is the biologic nature of the tumor process in relation to its spatial configuration. This is also the important factor determining curative tumor dose. With the exception of very small tumors and certain important radiosensitive conditions, it is the effect on normal tissues which defines the limits of irradiation and which effectively determines the prescription of dosage. The relationship between dose and volume is basic to this discussion and is considered with particular reference to the integrity of mesenchyme. When comparing the radiosensitivities of tumor and host tissues, it is important to compare like with like. The ultimate effect on a tumor is measured functionally, in terms of suppressing the only function by which the tumour is recognized--its capacity for indefinite proliferation--and reflected in 5- and 10-year cure rates. The effects on normal tissues should therefore be similarly measured in dynamic terms of the final functional state rather than on any transient structural appearance. These features are considered in relation to three different clinical situations: certain radiosensitive tumors, accessible primary tumors of limited sensitivity, and large tumors situated deeply. It is emphasized that curative treatment requires careful clinical appraisal of all the relevant features in each individual patient. The state of both tumor and host reaction may change significantly during the period of treatment and there is no alternative to continuous clinical observation using all the ancillary aids available.

Free radicals by mass spectrometry. XXXVIII. Primary steps in the mercury-photosensitized decompositions of dimethyl sulfide and dimethyldisulfide

The reaction between mercury (3P1) atoms and dimethylsulfide at 55 °C has been shown to be exclusively[Formula: see text]Two primary modes of dissociation have been established for the corresponding reaction with dimethyldisulfide.[Formula: see text]The former reaction accounts for ~20% of the primary decomposition at 55 °C. No reaction leading to H-atom removal was found for either compound.The subsequent reactions of CH3S and CH3SS radicals, chiefly combination and disproportionation, have been investigated briefly.

Mercury-photosensitized reactions in the presence of CO: decomposition of ethylenimine

The effect of CO addition on a number of Hg(3P1) photosensitized decompositions, under conditions of incomplete quenching, has been investigated. Compounds having large quenching cross sections (i.e. those presumably decomposing through formation of triplet excited states) have enhanced rates of decomposition in the presence of CO. Those having small cross sections (i.e. those for which the primary interaction is presumably the direct attack of Hg(3P1) atom on a C—H bond) show no enhancement. This difference in behavior, which is interpreted in terms of activation by a HgCO* complex, suggests that CO addition under the appropriate conditions can be used to decide whether or not certain decomposition products aries from an electronically excited precursor. For example, the effect of CO on the sensitized decomposition of ethylenimine indicates that the major dissociation process to form C2H4 and the NH radical proceeds by way of an electronically excited precursor, while a minor process (5%) to form

[Formula: see text] radical and a H-atom does not. Some results on the sensitized decomposition of formaldehyde are also discussed.

Attack of related free radicals on methane. Arrhenius parameters and thermochemistry

The Arrhenius parameters of some 20 reactions, in which different atoms and radicals attack methane, have been compared in the light of the thermochemistry of the reactions. Attention has been focussed on family relationships amongst the attacking species.Where direct kinetic data are lacking, Arrhenius parameters have been calculated from data available for the reverse reactions.