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Plots of the bond dissociation energies of the hydrides and fluorides are presented together with those for the corresponding isoelectronic ions derived from ionization potential data. These show the dependence of the energies on the closed shell configurations appropriate to the shape of the radical or ion. The curves are also used to derive certain proton affinities and to explain the feasibility of ion-molecule reactions. All the processes to be considered in the present article refer to the monomeric species and the bond dissociation energies are with reference to the lowest states of the atoms, radicals or ions. Exceptions to the latter statement occur for NH, HF and Ne+F where the removal of a pπ electron does not lead to the lowest state of the ion.

A detailed description of how the electron cloud holds the various nuclei of a molecule together has for many years been the objective of the chemist, since this is fundamental to his subject and essential to its progress. The difficulties of acquiring this knowledge have now been largely overcome with the development of the technique of photoelectron spectroscopy. Using monoenergetic photon sources, such as the emission line of helium at 58.4 nm (21.22 eV), outer electrons can be ejected and their binding energies measured (EB = hv—½mv2). Thus a quantitative description of the electronic environment of the nuclear framework is available for relating the electrical to the chemical properties of a molecule. The present review deals with the ultraviolet photoelectron spectroscopy (UPS) of basic type molecules, illustrates the main features of the technique, and shows how the electronic structure determines the size and shape of the molecule. Much use is made of the isoelectronic principle to relate...

Photoelectron spectra of the monomeric species of several classes of ionic molecule have been obtained by crossing a molecular beam of the material with a photon beam containing photons of energies up to 50 eV (He I and He II lines). In this way electrons from the s 2, p 6 and d 10 shells of the relevant atoms (or ions) were ejected and studied by photoelectron spectroscopy. The spectra are found to be explicable in terms of simple ionic models in which polarization of both negative and positive ions but mainly the former are taken into account. Work is reported on the alkali halides and the halides of Tl, In, Sn and Pb.

THE FAILURE of viruses to multiply except within living cells has led to considerable speculation regarding the essential materials or conditions necessary for their reproduction. Holmes (23) recently approached the problem from the standpoint of the taxonomic affinities of plant species found to be susceptible or insusceptible to tobacco-mosaic virus (Marmor tabaci H.).2 He found that classification of tested species of plants into four groups according to their natural relationships revealed a group consisting of only susceptible species, a group of largely susceptible species, a group made up of about half susceptible and half insusceptible species, and a group of mostly insusceptible species. Holmes suggested that there may be an orderly distribution in nature of substances or conditions necessary for multiplication of the virus. If this interpretation is correct, other plant viruses might show a similar tvpe of host distribution. A comparison of the host ranges of several plant viruses might lead to a knowledge of certain differences and similarities in specific chemical or physical properties required bv viruses for reproduction. With this idea in mind, plants belonging in a large number of families have been tested for susceptibility to six different viruses. The results of the tests are presented herewith. MATERIALS AND METHODS.-Virus stocks.-The following plant viruses were used: Tobacco-necrosis virus (Marmor lethale H.). Cucumber-mosaic virus (M. cucumeris H. var. vulgare H., judicis H., and vignae H.); most tests were made with the ordinary strain, vulgare. Cucurbit-mosaic virus (M. astrictum H. var. aucuba H.). Alfalfa-mosaic virus (M. medicaginis H. var. typicum Black and Price). Tobacco-ringspot virus (Annulus tabaci H. var. virginiensis H.). Tomato-ringspot virus (A. zonatus H.). The table to be considered presently includes results of other workers with additional virus strains. Most of these strains are listed in the Handbook of Phytopathogenic Viruses (24). One strain not listed there but included in the table is the potato-calico strain of alfalfa-mosaic virus (Marmor medicaginis var. solani Black and Price), only recently shown to belong in the alfalfa-mosaic virus group (7). The virus stocks were transferred to young plants at frequent intervals in order to insure a high virus content in the juices to be used as inoculum. Cucumber (Cucumis sativus L.) served as a source plant for cucurbit-mosaic virus, Turkish tobacco (Nicotiana tabacum L.) as a source plant for the other

The theory of infra-red reflection spectra has been applied (i) to obtain the frequencies and extinction coefficients of the intense absorption bands in polytetrafluorethylene near 8.5 microns, (ii) to determine the number and states of polarization of the fundamental NH stretching absorption bands in a crystal of urea. The reflection method has definite advantages over transmission measurements in both cases.

The absorption spectra of the ethyl and higher halides have been examined in the region 2000–1000A. It has been found that they are essentially similar to those of the methyl halides. The ionization potentials of ethyl iodide are given as 9.30 and 9.88 volts and those of ethyl bromide as 10.24 and 10.56 volts. The ionization potentials of the higher halides cannot be determined exactly because of the presence of continuous absorption from the C–C and C–H bonds, and of the diffuseness of the bands themselves. However there is strong evidence that the ionization potentials of consecutive members of the homologous series diminish asymptotically to a limiting value, the diminution from methyl to ethyl being by far the greatest. A comparison of the way the ionization potentials diminish and the dipole moments of the carbon‐halogen bonds increase as we ascend the homologous series indicates a definite connection between the two phenomena.

The absorption spectrum of diborane has been investigated in the infra‐red from 1–25μ and in the vacuum ultraviolet down to 1000A. The rotational structure obtained for certain of the infra‐red bands rules out the ethane‐type structure but agrees very well with the interpretation of the electron diffraction results in terms of a bridge model. The ultraviolet spectrum indicates a simple electronic structure and a first ionization potential about 11–12 volts.

Recent progress in the design and construction of photoelectric spectro-photometers is reviewed. Their associated equipment, such as low-voltage hydrogen lamps, electronically stabilized power packs, ultra-violet sensitive photocells, etc., is discussed. Double-beam recording spectrophotometers and methods of cathode-ray presentation of spectra are described and an account is given of the methods of ultra-violet microspectro-photometry. Developments in the vacuum ultra-violet, solar spectroscopy, high intensity light sources, photographic emulsions, etc., are discussed and progress in the interpretation of ultra-violet absorption spectra is reviewed.

The absorption spectra of formaldehyde and of compounds of the type HOH, ROH, ROR and HSH, RSH, RSR have been observed in the region 2300–1000A. An analysis of the spectrum of formaldehyde yields a value of 10.83±0.01 volts for the first ionization potential of the C=O bond and about 164 Cal./mole for the strength of this bond. The spectra of the alkyl derivatives of H2S are all shown to be shifted to the long wavelength region relative to those of H2O. Rough estimates of their ionization potentials are given and the influence of dipole moment on the ultraviolet absorption spectra and ionization potentials of polyatomic molecules is discussed.

The Christiansen filter effect in slurries of organic crystals is reported for the first time, in the infra‐red. The main difference between the effect in molecular and in ionic crystals is that the Christiansen (transmission) peak and the ``Reststrahlen'' (reflection) peaks are much closer together for organic crystals since they are produced by a single frequency instead of a wide band of lattice frequencies. The Christiansen effect is much more selective in organic crystals since it occurs for some bands but not for others. This is thought to be due to the nature of the coupling between the particular vibration and the atoms or groups in the molecule which make major contributions to the polarizability.

An absorption spectrum of acetylene in the region 1520A to 1050A has been found. It appears at very low pressures. The analysis was made by obtaining the spectrum of acetylene made from about 50 percent heavy water. The small isotopic shifts of many bands revealed them to be vibrationless electronic transitions. These are arranged into two Rydberg series going to the same limit which corresponds to an ionization potential of 11.35 volts. The upper levels of the two series are designated as $\mathrm{np}\ensuremath{\Sigma}$ and $\mathrm{np}\ensuremath{\Pi}$ levels. The excitation and ionization are from the CC bond and only vibrations affecting this bond appear. The character of the vibrations present is deduced from the magnitude of the isotopic shifts. Strong predissociation occurs around 1520A. This yields a value of about 187 Cal/mole for the strength of the triple CC bond. A similar set of bands appears in ethylene in the region 1750A to 1200A. The bands are more diffuse than those in acetylene, and only one strong Rydberg series was discovered. The limit of the series corresponds to an ionization potential of 10.41 volts. The vibrational analysis is similar to that in acetylene. The spectrum of ethane is extremely diffuse and no analysis of it could be made. It is concluded that, as in methane, all the upper states are unstable.

Two Rydberg series of bands of NO which converge to a common limit at 175200+or-50 cm-1 (21.721+or-0.006 eV) have been found in absorption in the range 680-560 AA. The limit agrees with an ionization peak occurring at this energy in its photoelectron spectrum. The ionization is interpreted as leading to the formation of the ( sigma *2s)-1, 3 Pi state of No+. No comparable band systems which could be assigned as Rydberg bands approaching the corresponding singlet state. This phenomenon is attributed to configuration interaction affecting preferentially the low multiplicity component of spin-split stages. It appears to be a common feature of the inner valence orbitals of many paramagnetic molecules and their ions. The diffuseness and Fano type profiles of many of the bands of NO show that the life-times of the states are very short due to predissociation and autoionization.

The absorption spectra of C6H6 and C6D6 have been photographed under high dispersion in the region 2000–1000A. The spectra of both substances are very similar. A strong continuous absorption starts fairly sharply around 1840A and gradually weakens out to zero at 1600A. It is followed by a region extending down to about 1360A which contains very strong sharp bands. The strongest of these bands only suffer small shifts to the violet in going from C6H6 to C6D6. This shift which is due to the change in the difference of zero‐point energy between the normal and the excited states reveals the bands to be vibrationless electronic transitions. It was found that these bands could be arranged into two Rydberg series which had approximately the same limit corresponding to an ionization potential of 9.190±.005 volts for C6H6. The ionization potential of C6D6 is only about 3 × 10—4 volts greater than that for C6H6. All the electronic states are split up into patterns which are believed to be caused by true electronic multiplicity. The excitation is apparently from a nonbonding electron more strongly attached to the carbon atom. The vibrations which accompany the bands are comparatively weak. However for C6H6 the following vibration frequencies associated with the excited states were observed. ω1 = 677 cm—1, ω2 = 968 cm—1. These become 630 and 926 cm—1 for C6D6. Tentative assignments of their modes of vibration are made. The bands below 1360A are considerably more diffuse than those previously mentioned and the isotopic shifts to the violet are much larger for these bands. However they are still believed to be vibrationless electronic transitions though they are due to the excitation of an electron which is considerably more bonding than that corresponding to the first ionization potential. A consideration of them enables the approximate value 11.7±.3 volts to be predicted for the second ionization potential of benzene.

THE QUESTION of how viruses produce their characteristic effects in plants is of major interest to virologists. A possible answer is that they do so by utilizing protoplasmic or other constituents that are essential for normal development of host cells. Total depletion of such essential materials could result in death of cells while partial depletion could lead to decreased vigor, reduction in size, loss of color, or other characteristic effects. No doubt, depletion of essential host cell constituents accounts for some of the changes induced by viruses. However, there is evidence that other mechanisms are involved. The fact that severity of symptoms is not necessarily correlated with virus concentration suggests that virus multiplication is accompanied by production of specific materials that have deleterious effects on cells in which they arise. The fact that toxic substances have been demonstrated in some virus-infected plants (Kraybill et al., 1932) supports this suggestion. The similarity in effects of viruses and auxins, or growth-regulating substances, noted by a number of investigators (Zimmerman and Hitchcock, 1941, 1942; Thomas and Riker, 1943) suggested that additional information about virus activity in cells of their hosts might be ascertained by studying the combinatorial effects of viruses and growth substances. The changes induced by applications of beta-napthoxyacetic acid (B-NOA), 2,4-dichlorophenoxyacetic acid (2,4-D), and parachlorophenoxyacetic acid (P-CPA) separately and in combination with Southern Bean Mosaic (SBM) virus (Zaumeyer and Harter, 1942) have been compared with those induced by SBM virus alone. Similar but less extensive studies were carried out with aster yellows virus. It is the purpose of this paper to describe the experiments and to report the results obtained. REVIEW OF LITERATURE.-The physiological activity of beta-napthoxyacetic acid (B-NOA) was first reported by Irvine in 1938 who compared its effects when applied in lanolin to the effects of X-radiation in plants. It was later reported to be active when applied as a vapor or in solution (Zimmerman and Hitchcock, 1939). B-NOA was the first substance observed to possess ability to produce formative effects in leaves and flowers (Zimmerman and Hitchcock, 1941). Para-chlorophenoxyacetic acid (P-CPA) and 2,4-dichlorophenoxyacetic acid (2,4-D) were subsequently found to

The far ultraviolet absorption spectrum of oxygen has been photographed under high dispersion in the region 1300-650A. The bands are explained as going to the various excited states of $\mathrm{O}_{2}^{}{}_{}{}^{+}$ as limits and are attributed to the removal of $v\ensuremath{\pi}$, $\ensuremath{\omega}\ensuremath{\pi}$ and $x\ensuremath{\sigma}$ electrons, respectively, from the normal state of ${\mathrm{O}}_{2}$. The results strongly support Mulliken's assignment of the visible $\mathrm{O}_{2}^{}{}_{}{}^{+}$ bands to the transition $^{4}{\ensuremath{\Sigma}}_{g}^{\ensuremath{-}}\ensuremath{\rightarrow}^{4}\ensuremath{\Pi}_{u}$. The distances of the $^{4}\ensuremath{\Pi}_{u}$ and $^{4}{\ensuremath{\Sigma}}_{g}^{\ensuremath{-}}$ states of $\mathrm{O}_{2}^{}{}_{}{}^{+}$ from the ground state of ${\mathrm{O}}_{2}$ are given as 16.1 and 18.2 volts, respectively, with possible errors of about a tenth of a volt. The appearance and nonappearance of strong electronic series going to known ionization potentials are also discussed.

Photoelectron spectroscopy is concerned with the ejection of electrons from atomic systems according to the Einstein photoelectric equation. E is the initial binding energy (ionization energy) of the electron and ½mv2 the kinetic energy it acquires when ejected by a photon of frequency v.

The design and construction of a vacuum ultra-violet monochromator suitable for photo-electric spectrophotometry and photo-ionization studies at short wavelengths is described. It incorporates a device for moving the exit slit along the beam to keep the spectrum in focus as the grating is rotated. The tank is divided transversely into two sections for permitting easy adjustment or interchange of gratings without disturbing the driving mechanism. An elaborate system of baffles is used to reduce scattered radiation to a very low value. A variety of attachments fit on to the exit slit for the examination of solid, liquid or gaseous samples and for photoelectric or photo-ionization measurements.

To sum up briefly, the data accumulated during the past decade show conclusively that plants infected with certain virus diseases develop a defense reaction beyond the natural immunity inherent in the plant. There are some virus diseases from which plants recover and become refractory to reinfection. The immunity that ensues is of the carrier type, since the plant continues to harbor the virus. In many instances-in all instances so far studied-plant cells infected with one strain of a virus become immune from infection with a closely related strain. In this case, the immunity is usually of the chronic-disease type, since the plants lose neither the virus nor the symptoms produced by the virus. In both types of immunity, the nature of the defense mechanism is unknown. The nature of the mechanism is of importance not only with respect to plant virus diseases but also in the general field of immunity as a whole, for even in animal diseases the exact nature of the defense reaction is by no means solved. It is...

The absorption spectra of aluminum, lithium, and sodium borohydride have been obtained in the region from 1–25μ. The aluminum borohydride was investigated as gas and an analysis of the infra‐red and Raman bands fits a bridge‐type structure of symmetry D3 (probably D3h). The spectra of lithium and sodium borohydrides were obtained from finely ground slurries of these materials. Their spectra indicate how the bridge structure of the H2BH2 metal groups passes over to the tetrahedral structure in a completely ionic lattic.Using certain bond‐distance force‐constant relationships in conjunction with data from the diatomic hydrides and accepting electron and x‐ray diffraction data for bond distances between the heavier atoms, values for the geometrical parameters are calculated for beryllium, aluminum, and sodium borohydride. These seem more plausible than any so far suggested. Observations on the electronic spectrum of aluminum borohydride have also been made down to 1000A. The diffuseness of the absorption obt...

A double beam recording infra-red spectrometer is described which employs a monochromator and servo system of novel design. The double beam principle adopted is similar to that of Lehrer and Wright. The monochromator is compact and uses relatively cheap and readily available components. The performance of the instrument is shown by reproductions of typical spectrograms.

Thermal inactivations of tobacco-necrosis virus, tobacco-mosaic virus, alfalfa-mosaic virus and tobacco-ringspot virus were found to follow the course of a first order reaction. The rates of inactivation at a number of different temperatures were calculated for each of the 4 viruses. The energy of activation, orE value, for each was calculated from inactivation rates at different temperatures. TheE values, in calories per mole, were as follows: for tobacco-necrosis virus at 70–95° C., 37300; for tobacco-mosaic virus in undiluted juice at 68–84° C. and 84–95° C., 55300 and 195000, respectively; in juice diluted 1∶20 at 68–83° C. and 83–91° C., 92000 and 176000, respectively; in dried leaf material at 70–150° C., 24100; for alfalfa-mosaic virus at 50–62,5° C., 75000; and for tobacco-ringspot virus at 45–56,5° C. and 56,5–65° C., 78800 and 27600, respectively.

The spectra of three octenes, cyclohexene and 2,3‐dihydropyrane, and of octyne−1 and −2 were obtained in n‐heptane solution to 1700A. Intensity measurements on ethylene vapor to 1550A enable the contribution of the Rydberg bands to be separated from that of the continuum. The f‐values in ethylene and the octenes are about 0.30, agreeing with Mulliken and Rieke's theoretical prediction within the experimental uncertainty of about 20 percent. The f‐values of the octynes are about the same, but those of cyclohexene and dihydropyrane are about 0.20.

A grating spectrometer designed on an Ebert mounting has been constructed which, with suitable photoconductive cells and a 6 × 6 in. N.P.L. grating, gives a resolution of 0.1 cm-1 in the range 6000 to 1700 cm-1. It covers the region 600 to 10 000 cm-1 with a single grating and is as simple to operate as a conventional prism spectrometer. It is intended as a high resolution general purpose instrument which will give a performance an order of magnitude better than that of a prism instrument over the main spectral range.

DETAILED PROCEDURES for estimating the relative potency of drugs from the response induced in test animals by injection of graded doses were worked out by Bliss and Marks (1939a and 1939b). These procedures make it possible to calculate not only the most probable relative activity of the drug in terms of a standard, but also the limits within which the true activity will lie for any given level of significance. In recent work (Spencer and Price, 1943; Price and Spencer, 1943a, 1943b), the procedures of Bliss and Marks were applied in determining the accuracy of measuring the relative activities of certain plant viruses. From the results it was found that the relative activities of tobacco mosaic, tobacco necrosis, and tobacco ringspot viruses could be estimated with errors not exceeding 10, 11, and 14 per cent, respectively, under the prevailing experimental conditions and that the standard error of estimate was a reliable measure of the experimental error. The results with alfalfa mosaic virus were less satisfactory; the standard error of estimate could not be counted upon to give a reliable estimate of the true error. The present paper describes the results obtained when essentially the same procedures were applied in measuring the relative activity of southern bean mosaic virus (Marmor laesiofaciens Zaumeyer and Harter). THE VIRUS.-Southern bean mosaic virus was first described by Zaumeyer and Harter (1942, 1943) who found all tested varieties of bean (Phaseolus vulgaris L.) to be susceptible. In some varieties, reddish necrotic lesions about 1 mm. or less in diameter were produced on inoculated leaves, and the virus was localized in these lesions. In other varieties no symptoms appeared on inoculated leaves, but the virus became systemic and caused a mottling disease in the young leaves. More recently, a strain of the Blue Lake variety was found to develop a systemic necrosis when infected with the virus (Zaumeyer and Harter, 1944). Mottling type varieties serve as a means of propagating the virus and of obtaining it in relatively large quantities. Local lesion type varieties offer a means of determining the relative activity of virus samples used in experimental work. In the present work, the virus was propagated in the Bountiful variety of garden bean and its activity was determined by inoculation of the Early Golden Cluster variety.2 The virus samples used in the rela

The ionization potentials of NO2 up to 28 eV have been measured using He i and He ii high‐resolution photoelectron spectroscopy. The assignment of the ionized levels below 16 eV is straightforward, including the singlet–triplet splittings, and allows us to assign Rydberg series in the vacuum uv leading to the first five ionization potentials. Above 16 eV the spectrum is complicated by the absence of obvious singlet–triplet splittings. The assignments we propose fit in with a coherent scheme for the molecular‐orbital energy levels of 16‐, 17‐, and 18‐electron triatomic molecules. The SCF calculations have been performed on several states of NO2 and NO2+ (both open shell and closed shell) and the results are in quite good agreement with the experimental ionization potentials.

The absorption spectra of H2O and H2S in the region below 1600A have been found to consist of various electronic series accompanied by comparatively little vibrational structure. The electronic series conform fairly well to Rydberg formulas the limits of which give 12.56±0.02 and 10.42±0.01 volts, respectively, for the ionization potentials of these molecules. The analysis fits in very well with Mulliken's prediction that the bands should be due to the excitation and removal of a nonbonding electron localized near the oxygen or the sulphur atom. A tentative rotational analysis given for some of the bands in H2S indicates that the moments of inertia suffer little change by the excitation. Suggestions with regard to plausible atomic term series related with the molecular series are put forward.

SummaryShadowed electron micrographs of mixtures of purified southern bean mosaic and bushy stunt viruses with their specific antisera show their spherical elementary bodies aggregated into microflocs in which the particle-separations seem to be about twice their normal values. More detailed electron micrographic study of these systems is underway.

Statistical comparisons indicate that within 12 hours of birth the serum protein-bound iodine of the infant is of the same order of magnitude, on the average, as that present in maternal blood during pregnancy or within a few hours of delivery. During the remainder of the first week of life there occurs a transient statistically significant increase in the mean value of this iodine fraction. During the sixth to twelfth week the concentrations fall below those present neonatally, but at this time or at any subsequent age up to 1 year, they are still on the average above those encountered in euthyroid nonpregnant adults or in older children. The possible relationship of these higher mean values in infancy to increased thyroid function in the rapidly growing infant have been mentioned with emphasis on the elevated concentration of circulating thyroxin.

The construction of a simple photoelectron spectrometer for the study of molecular ionisation potentials is described. It has operated routinely in a teaching laboratory for five years with little maintenance. It is basically a slotted-grid retarding-potential analyser with a helium source and an inexpensive transistorised electrometer. A resolution of 25 meV (FWHM) can be obtained on the argon doublet and this is sufficient to resolve vibrational structure in the photoionised states of oxygen, nitrogen, hydrogen, deuterium, etc. The spectra reveal the electronic structure of atoms and molecules in a direct way making the orbital shell structure immediately evident to the student.