308 lines
12 KiB
Plaintext
308 lines
12 KiB
Plaintext
Ko. 3805, OCTOBER :,, 1942
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NATURE
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405
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Anemotaxis in Drosophila
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CoLE 1 has observed that Drosophil,a melanogaster rnmetimes walks against an air current. Fliigge2 showed that this reaction only occurred when the air was scented, and must therefore be regarded as orientation by smell. However, reactions to air currents without smell do occur in Drosophila.
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Comparing several species of the genu:;;, a division can be made between those which show a distinct positive anemotaxis and those which do not.
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Drosophila virilis +, D. virilis americana, D. subob-
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scura and D. junebris turn very sharply toward~ a tube from which air is flowing and start walkmg against it, so long as they are not blown away. D. melanogaster and D. buskii, on the other hand, show no reaction, whereas D. pseudo-obscura shows a slight reaction.
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Removal of the wings or antennre or both does not abolish the reaction in the species showing it. Therefore Fraenkel and Gunn's• contention that anemotaxis depends on the perception of body deformation caused by the wind seems plausible for Drosophila.
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The fact that the two light species observed do not react to wind whereas the four dark species do, may be an indication that the former are not exposed to strong air currents in their natural environment, while the latter are. As wind is a factor which increases evaporation, this is in agreement with some recently published deductions', to the effect that a dark cuticle provides better protection against desiccation than a light one.
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H. KALMUS.
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Department of Biometry, University College, London, at Rothamsted Experimental Station,
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Harpenden, Herts. Sept. 3.
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1 Cole, W. H., J . .A.nim. Behaviour, 7. 71 (1917). 'Fliigge, C., Z . veryl. Physiol., 23, 463 (1934). 'Fraenkel and Gunn, "Orientation of Animals" (Oxford, 1940). 'Kalmus , H., NATURE, 1':8, 428 (1941).
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Nomenclature of Biological Movement
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HAVING read recently with very great interest Friienkel and Gunn's "Orientation of Animals", I set about making for my own clarification a classification of all the cases I know of what used to be called 'tropistic' movements.
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It is clear that three major groupings are possible: a taxis, which is a bodily movement of an animal or motile plant in a direction determined by the direction of the stimulus ; a kinesis, which is a change of rate of movement of an animal (or perhaps motile plant) in response to a change of intensity of a stimulus, but not in a direction determined by the direction of the stimulus-and often producing an aggregating effect superficially similar to that of a taxis ; and an orientation, which is the placing of the body (usually if not always animal) in a direction d etermined by the direction of the stimulus. To these three classes many of the cases can be referred.
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But the responses of sessile plant organs do not siiem to be so conveniently classified. The thigmotropism of Clematis tendrils appears to warrant that name, for the response is a directional one. But the same cannot be said of the so-called 'thigmotropism' of Mimosa leaflets, Mimulus stigma or Berberis
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stamen, for here the response is not in a direction determined by that of the stimulus. The r esponse in these cases appears to bear a closer resemblance to the photonasty of Oxalis leaflets and the thermonasty of Tulipa flowers. Is one then justified (disregarding-as often becomes necessary for purposes of coherence-mere etymological niceties) in putting these responses under the heading of 'thigmonasty' (or possibly in some cases--a~ in Stiles's "Plant Physiology"-'seismonasty') ? By the same token may the response of Mimosa leaflets to a lighted match in the neighbourhood be called a 'thermonasty', and t;n ammonia vapour, a 'chemonasty' ?
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CYRIL BIBBY. 20 Dellcott Close, Welwyn Garden City.
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Sept. 4.
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An Inland Record of Triglochin maritimum L.
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IN a previous note1 I recorded the occurrence of the halophilic alga Percur8aria percursa Rosenv. from a salt-spring situated at Aldersey 2, Cheshire. Continuing the ecological survey of this spring, I am now able to report the presence of the halophyte Triglochin maritimum L. (Naiadacere). It occurs in three small colonies growing in the salt-spring and appears to be well established. I should add that during the past year the spring has maintained a salinity of 1,642 parts per 100,000 with only slight variation.
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Triglochin maritimum, popularly known as seaside arrow-grass, is a plant frequently found in salt marshes. Its oceurrence in a non-littoral region is exceptional and would seem to be unique in so far as the county of Cheshire is concerned. Search of the literature has revealed t;he fact that Triglochin has occasionally been recorded from the counties of Cambridgeshire, Staffordshire and Surrey.
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In Cambridgeshire, the plant appears to have been fiest reported from Tydd Marsh by Skrimshire3• A.~Evans•, however, points out that it, was never plentiful in that county and has not been found there during recent years. In Staffordshire, J. E. BagnalJS mentions records of Triglochin by the independent observers, Shaw, Stokes and Brown. In Surrey, C. E. Britton6 records its discovery by W. A. Todd from the Thames near Putney.
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I am indebted to Mr. A. A . Dallman, of Doncaster, for certain of the references quoted.
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FREDERICK BURKE.
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12 Queen's Road, Chester. Aug. 29.
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1 Burke, F., NATURE, 149, 331 (19!2). 'Sherlock, Mem. Geo!. Survey, Minera l Resources of Gt. Brit. , Rock-
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salt and Brine, 18, 111 (1921). • Relban, R ., "Flora Cantabrigiensis", second edition, 145 (1802). • Evans, A. E., " Flora of Cambridgeshire", 165 (1939). • Bagnall, J. E ., "Flora of Staffordshire", 57 (1901). • Britton, C. E., J . Bot., 48, 186 (1910).
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Existence of
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Electromagnetic-Hydrodynamic Waves
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IF a conducting liquid is placed in a constant magnetic field, every motion of the liquid gives rise to an E.M.F. which produces electric currents. Owing to the magnetic field, these currents give mechanical forces which change the state of motion of the liquid.
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© 1942 Nature Publishing Group
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406
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NATURE
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OCTOBER :{, 1942, VOL. 150
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Thus a kind of combined electromagnetic-hydro-
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dynamic wave is produced which, so far as I know,
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has as yet attracted no attention.
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The phenomenon may be described by the electrodynamic equations
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rot H
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=
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4-rr
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.
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i
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C
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rot E =
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,J,B
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c dt
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B = µH
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i =
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a(E
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+
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V -
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C
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X
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B);
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together with the hydrodynamic equation
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a d--vdt
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=
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c l
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. (i
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X
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B) -
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grad p,
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where cr is the electric conductivity,µ the permeability,
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othe mass density of the liquid, i the electric current,
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v t,he velocity of the liquid, and p the pressure.
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Consider the simple case when cr = oo , µ = 1 and
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the imposed constant magnetic field H0 is homogeneous and parallel to the z-axis. In order to study
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a plane wave we assume that all variables depend
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upon the time t and z only. If the velocity v is par-
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allel to the x-axis, the current i is parallel to the
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y-axis and produces a variable magnetic field H' in
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the x-direction. By elementary calculation we obtain
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d 2H I
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4no d 2H'
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dz 2
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H 0 2 dt2 '
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which means a wave in the direction of the z-axis
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with the velocity
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Ho .
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V = v'4n8
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Waves of this sort may be of importance in solar physics. As the sun has a general magnetic field, and as solar matter is a good conductor, the conditions for the existence of electromagnetic-hydrodynamic waves are satisfied. If in a region of the sun we have
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Ho = 15 gauss and o = 0·005 gm. cm.-3, the velocity
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of the waves amounts to
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V ,...._, 60 cm. sec.-1•
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This is about the velocity with which the sunspot
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zone moves towards the equator during the sunspot
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cycle. The above values of H O and orefer to a distance
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of about 1010 cm. below the solar surface where the
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original cause of the sunspots may be found. Thus
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it is possible that the sunspots are associated with a
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magnetic and mechanical disturbance proceeding as
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an electromagnetic-hydrodynamic wave.
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The matter is further discussed in a paper which
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will appear in Arkiv for matematik, astronorni och
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fysik.
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H. ALFVEN.
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Kg!. Tekniska Hogskolan, Stockholm. Aug. 24.
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Energy of Dissociation of Carbon
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Monoxide
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THE energies of dissociation of a number of diatomic molecules have been determined from spectroscopic data, apparently with high accuracy, by the observation of predissociation limits. During the last few years the following values have been proposed for
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CO: D(CO) = 6·92 ', 8·41 2, 9·14 •, 10·45 4 e.v.;
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while values of 9·85 and 11 ·11 also appear possible3• Controlled electron experiments suggest 9 ·6 5•
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The value obtained by extrapolation of the vibra-
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tional levels of the ground state is about 11, and sup-
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port for this value has been given by Kynch and
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Penney6. Herzberg1 has recently summarized evi-
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dence favouring 9·14.
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At first sight, the strongest argument for 9·14 is
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the observation by Faltings, Groth and Harteck8 that
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CO is decomposed by the xenon line at 1295 A.,
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but not by that at 1470 A., from which they con-
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clude that 8·44 < D(CO) < 9·57. This conclusion
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is not based on an examination of the initial act of
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absorption. The only known absorption in the
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1295 A. region is that corresponding to the fourth
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positive bands. The origins of the (9,0) and (10,0)
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bands lie at 76,839 cm.-1 and 78,010 cm.-1. The xenon
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line 1295A. = 77,172 cm.-1 falls between these bands
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and, if absorbed from the lowest vibrational level of
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CO, would correspond approximately to the line
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P(35) of (10,0). This gives as the upper limit of
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D(CO) (when the rotational energy is taken into
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account) a value of 79,722 cm.-1 = 9·88 e.v. (not
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9·57 e.v. as stated by Herzberg7). Actually, it is
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doubtful whether such a high rotational line as P(35)
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would be observed at room temperature, and absorp-
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tion, if it is due to CO, would probably occur from a
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higher vibrational level, corresponding perhaps to the
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(13,2) band, in which case the dissociation limit may
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be placed as high as 10 •I.
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Taking the first act of absorption as
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CO(X1 I:) + hv = CO(A 1IJ),
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and assuming a life not less than 10-• sec. for A 111,
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then at atmospheric pressure each molecule ex-
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periences at least 100 collisions before radiating. It
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seems to us that this gives a reasonable chance for
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a reaction such as
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co. + CO(A 1II) CO(X1 1:) =
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+ C
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to proceed with quantum efficiency approaching unity.
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The state of the carbon atom might be either 'D or
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ap; the former if spin is to be conserved, the latter
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if not. In either case the reaction is strongly exo-
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thermic. The failure of the xenon line 1470 to induce
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photodissociation may be due to the reaction requir-
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ing an activation energy.
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Estimates of D(CO) less than 10 take no account
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of the non-crossing rule of Hund, and Neumann and
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Wigner0• This rule states that potential energy
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curves of molecular states of identical species cannot
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cross. Whether the rule is rigorous when the nuclear
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and electronic motions are not separated needs further
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examination, but at least we see no reason for antici-
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pating a failure of the rule in the lowest energy curve
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of CO. If this curve has only one turning point then
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the non-crossing rule requires unequivocally that
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D(CO) > 10·3, and would agree well with the pre-
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dissociation limit at 11 •ll e.v.
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The dissociation energy of CO+ is 2·6 e.v. less than
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that of CO (D(CO+) = D(CO) + l(C) - l(CO) ).
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Three electronic states of CO+ are known, namely,
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x• I;+, A•11 and B 2 I;+, extrapolating to dissociation
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limits of about 9·8 (a very long extrapolation), 9·2
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and 9·4 e.v. respectively. Since the two 2 I:+ states
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must give different products of dissociation, it would
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appear, on the evidence of the B 2 :E+ state, that
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D(CO+) is 7·4, and D(CO) is about 10, and on the
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evidence of the A 211 state that D(CO+) is 9·2 and
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D(CO) is 11 ·8. All that may fairly be deduced from
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present evidence on CO+ is that D(CO) is unlikely
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to be much less than 10.
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We have also re-examined nitrogen. The accepted
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value D(N2) = 7·38 is based on the identification of
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the upper state of the Vegard-Kaplan bands with the
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© 1942 Nature Publishing Group
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