The validity of the “few-level” approximation in gaseous relaxation phenomena

The Bloch equations including damping are formulated for a molecular system excited by incident radiation. In contrast with a previous treatment the present formalism gives an intuitively satisfactory form of relaxation terms. A three-level system irradiated by a single oscillating field is specifically considered, and using this manifold as a model for a two-level system immersed in a heat bath, the problem of “embedding” a pair of levels connected by radiation within a multi-level manifold is treated. A brief discussion of transient solutions to the Bloch equations is included.     

The variation of speckle size with film density: An example of Babinet's principle

The variation of the size of photographically recorded laser speckle with film density is compared with the predicted speckle size. The ten percent increase in the recorded speckle size and high average film densities is due to the non-linear film response and is an example of Babinet's Principle.     

Irreversible enzyme inhibitors. LXXXIX. candidate active-site-directed irreversible inhibitors of dihydrofolic reductase. X. derivatives of 2-amino-5-benzamidopropyl-4-pyrimidinol

Since 2-amino-5-benzamidopropyl-6-methyl-4-pyrimidinol (VII) was a reasonably good reversible inhibitor of dihydrofolic reductase, the benzamido group was substituted with p-bromomethyl (XVIIa), m-bromomethyl (XVIIIa), and p-bromoacetyl (XIXa) groups; these compounds, and the corresponding 6-phenylpyrimidines, were synthesized from the proper 2-amino-5-aminopropyl-4-pyrimidinol (V) by devising methods that were compatible with the high reactivity of the halogen. Compounds XVII-XIX showed in-activation of dihydrofolic reductase; the fact that p-nitrobenzyl bromide inactivated the enzyme as rapidly as XVII and XVIII and phenacyl bromide inactivated the enzyme as rapidly as XIX indicated that these inactivations proceeded by a random bimolecular mechanism and not the desired active-site-directed mechanism.     

Dihydropyridazines. III . Reactions with oxygen

The reactions of oxygen with a series of dihydropyridazines have been explored. The primary reaction other than aromatization appears to occur from the 1, 4-dihydro tautomer. A single crystal x-ray structure has been determined on the product from the reaction of oxygen with 3, 6-diphenyl-4, 4-dimethyl-1, 4-dihydropyridazine.     

Magnetic properties of 166Er and the collective model

The E2/M1 admixtures for nine γ-ground band transitions in ¹⁶⁶Er were measured. Mixing ratios, δ(E2/M1), were calculated based on a general treatment of magnetic properties in the framework of the collective model. The agreement with the experimental values is generally good.