中考励志句子-客服工作职责

39,164
1932
AHydrogenIsotopeofMass2,edde,
ColumbiaUniversityandtheBureauofStanda rds
(ReceivedDecember5,1931)
Theproton-elect ronplotofknownatomicnucleishowssomerather
marke dregularitiesamongatomsofloweratomicnumber
1
.UptoO
16
a
simplestep-wisefigureappearsi ntowhichthenuclearspeciesH
2
,H
3
and< br>He
6
couldbefindMenzel
2
haveshownth atthe
discrepancybetweenthechemicalatomicweight ofhydrogenandAston’s
valuebythemassspectrograph couldbeaccountedforbytheassumption
ofahydrogeni sotopeofmass2presenttotheextentof1partin4500parts< br>ofhydrogenofmass1.
Itispossibletocalculatewi thconfidencethevaporpressuresofthepure
substance sH
1
H
1
,H
1
H
2
,H
1< br>H
3
,
isonlynecessarytoassumethatinthe Debyetheoryofthesolidstate,Θis
inverselyproport ionaltothesquarerootofthemassesofthesemoleculesand
thattherotationalandvibrationalenergiesofthemo leculesdonotchange
ssumptionsareinaccordwithwel l-
findthatthevaporpressuresfor
thesethreemol eculesinequilibriumwiththeirsolidsshouldbeintherat io
ofp
11
:p
12
:p
13
=1:0.37 :oryoftheliquidstateisnotso
wellunderstoodbutit seemsreasonabletobelievethatthedifferencesin
vap orpressureofthesemoleculesinequilibriumwiththeirli quidsshouldbe
ratherlargeandshouldmakepossiblea rapidconcentrationoftheheavier
isotopes,iftheye xist,intheresiduefromthesimpleevaporationofliquid< br>hydrogennearitstriplepoint.
Accordinglytwosa mplesofhydrogenwerepreparedbyevaporatinglarge
q uantitiesofliquidhydrogenandcollectingthegaswhiche vaporatedfrom
firstsamplewascollected
1
2< br>Urey,.53,2872(1931);Johnston,ibid.,53,2866(1931 ).
BirgeandMenzel,.37,1669(1931).
1

fromtheendportionofsixlitersofliquidevaporatedat atmosphericpres-
sure,andthesecondsamplefromfou rlitersevaporatedatapressureonly
cessofliquefac tionhas
probablynoeffectinchangingtheconcentrati onoftheisotopessinceno
appreciablechangewasobse rvedinthesampleevaporatedatatmospheric
pressure .
Thesesampleswereinvestigatedfortheatomicspect raofH
2
andH
3
in
ahydrogendischarg etuberuninWood’sso-called“blackstage”byusing
th esecondorderofa21footgratingwithadispersionof1.31A permm.
Withthesampleevaporatedattheboilingpoint noconcentrationsohigh
increasedtheexposuressothattheratioofthetimeofexposuretotheminimumrequi redtogetthe
H
1
linesonourplateswasabout4 500:heseconditionswefound
inthissampleaswellasi nordinaryhydrogenfaintlinesatthecalculated
posi tionsforthelinesofH
2
accompanyingH
β
,H
γ
,H
δ
.Theselinesdonot
agreeinw ave-lengthwithanymolecularlinesreportedinthelitera ture
3
.
Howevertheyweresoweakthatitwasdi fficulttobesurethattheywere
notghostsofthestrongl yoverexposedatomiclines.
Thesampleofhydrogeneva poratednearthetriplepointshowsthese
linesgreatl yenhanced,relativetothelinesofH
1
,overbotht hoseofor-
dinaryhydrogenandofthefiativeintensiti escanbe
judgedbythenumberandintensityofthesymme tricalghostsontheplates.
Thewave-lengthsoftheH< br>2
linesappearingontheseplatescouldbeeasilylowingtablegivesthemeanofthe
observeddisplace mentsoftheselinesfromthoseofH
1
andthecalcul ated
displacements:
Line
∆λcalc.
∆λobs .
Ordinaryhydrogen
1stsample
2ndsample
H
α
1.793
—
—
1.820
H
β
1 .326
1.346
1.330
1.315
H
γ
1.185
1.206
1.199
1.176
H
δ
1.119
1.145
1.103
—
TheH
2
linesarebroad, asistobeexpectedforcloseunresolveddoublets,
but theyarenotasbroadanddiffuseastheH
1
linesprob ablyduetothe
smallerD¨ghtheirintensitiesrelativ etotheghosts
Gale,MonkandLee,Astrophys.J.57,89( 1928);Finkelnburg,52,57
(1928);Connelly,.42,28( 1929).
3
2

oftherespectiveH
1linesappearnearlyconstantforanyonesampleof
hy drogen,theyarenotghostsfortheirintensitiesrelative totheknown
ghostsarenotthesameinthecaseofordina ryhydrogenandofthe1st
enotmolecular
linesfor theydonotappearonaplatetakenwiththedischargetubein
the“whitestage”withthemolecularspectrumenhance dH
2
γwasfound
asaslightirregularityonami crophotometercurveofthisplate).Finally
theH
2
α,lineisresolvedintoadoubletwithaseparationof about0.16Ain
agreementwiththeobservedseparation oftheH
1
αline.
Therelativeabundanceinord inaryhydrogen,judgingfromrelativemin-
imumexpos uretimeisabout1:4000,orless,inagreementwithBirgean d
Menzel’arestimateoftheabundanceinthesecondsam ple
appreciablefractiona-
tionhasbeensecured asexpectedfromtheory
4
.
NoevidenceforH2
hasbeensecured,butitslineswouldfallonregion s
ofourplateswherethehalationisbad.
Thedisti llationwascarriedoutattheBureauofStandardsbyoneofu s
(F.G.B.),whoiscontinuingthefractionationtosec uremorehighlyconcen-
ctroscopicworkwasdoneatCol umbiaUniversity
bytheothertwo(.M.M.)whoareworki ngonthemolecular
spectrum.

edde

4
KeesomandvanDijk,dam34,52(1931).
3