The/at thermal/jj exchange/nn of/in chlorine/nn between/in Af/nn and/cc liquid/jj Af/nn is/bez readily/rb measurable/jj at/in temperatures/nns in/in the/at range/nn of/in 180-degrees/nns and/cc above/rb ./.
The/at photochemical/jj exchange/nn occurs/vbz with/in a/at quantum/nn yield/nn of/in the/at order/nn of/in unity/nn in/in the/at liquid/jj phase/nn at/in 65-degrees/nns using/vbg light/nn absorbed/vbn only/rb by/in the/at Af/nn ./.
In/in the/at gas/nn phase/nn ,/, with/in Af/nn of/in Af/nn and/cc Af/nn of/in Af/nn ,/, quantum/nn yields/nns of/in the/at order/nn of/in Af/nn have/hv been/ben observed/vbn at/in 85-degrees/nns ./.
Despite/in extensive/jj attempts/nns to/to obtain/vb highly/ql pure/jj reagents/nns ,/, serious/jj difficulty/nn was/bedz experienced/vbn in/in obtaining/vbg reproducible/jj rates/nns of/in reaction/nn ./.
It/pps appears/vbz possible/jj to/to set/vb a/at lower/jjr limit/nn of/in about/rb Af/nn for/in the/at activation/nn energy/nn of/in the/at abstraction/nn of/in a/at chlorine/nn atom/nn from/in a/at carbon/nn tetrachloride/nn molecule/nn by/in a/at chlorine/nn atom/nn to/to form/vb Af/nn radical/nn ./.
The/at rate/nn of/in the/at gas/nn phase/nn exchange/nn reaction/nn appears/vbz to/to be/be proportional/jj to/in the/at first/od power/nn of/in the/at absorbed/vbn light/nn intensity/nn indicating/vbg that/cs the/at radical/nn intermediates/nns are/ber removed/vbn at/in the/at walls/nns or/cc by/in reaction/nn with/in an/at impurity/nn rather/rb than/in by/in bimolecular/jj radical/nn combination/nn reactions/nns ./.



Introduction/nn-hl 
Because/rb of/in the/at simplicity/nn of/in the/at molecules/nns ,/, isotopic/jj exchange/nn reactions/nns between/in elemental/jj halogens/nns and/cc the/at corresponding/jj carbon/nn tetrahalides/nns would/md appear/vb to/to offer/vb particularly/ql fruitful/jj possibilities/nns for/in obtaining/vbg unambiguous/jj basic/jj kinetic/jj data/nn ./.
It/pps would/md appear/vb that/cs it/pps should/md be/be possible/jj to/to determine/vb unique/jj mechanisms/nns for/in the/at thermal/jj and/cc photochemical/jj reactions/nns in/in both/abx the/at liquid/jj and/cc gas/nn phases/nns and/cc to/to determine/vb values/nns for/in activation/nn energies/nns of/in some/dti of/in the/at intermediate/jj reactions/nns of/in atoms/nns and/cc free/jj radicals/nns ,/, as/ql well/rb as/cs information/nn on/in the/at heat/nn of/in dissociation/nn of/in the/at carbon-halogen/nn bond/nn ./.
The/at reaction/nn of/in chlorine/nn with/in carbon/nn tetrachloride/nn seemed/vbd particularly/ql suited/vbn for/in such/jj studies/nns ./.
It/pps should/md be/be possible/jj to/to prepare/vb very/ql pure/jj chlorine/nn by/in oxidation/nn of/in inorganic/jj chlorides/nns on/in a/at vacuum/nn system/nn followed/vbn by/in multiple/jj distillation/nn of/in the/at liquid/nn ./.
It/pps should/md be/be possible/jj to/to free/vb carbon/nn tetrachloride/nn of/in any/dti interfering/vbg substances/nns by/in the/at usual/jj purification/nn methods/nns followed/vbn by/in prechlorination/nn prior/rb to/in addition/nn of/in radioactive/jj chlorine/nn ./.
Furthermore/rb ,/, the/at exchange/nn would/md not/* be/be expected/vbn to/to be/be sensitive/jj to/in trace/jj amounts/vbz of/in impurities/nns because/cs it/pps would/md not/* be/be apt/jj to/to be/be a/at chain/nn reaction/nn since/cs the/at activation/nn energy/nn for/in abstraction/nn of/in chlorine/nn by/in a/at chlorine/nn atom/nn would/md be/be expected/vbn to/to be/be too/ql high/jj ;/. ;/.
also/rb it/pps would/md be/be expected/vbn that/dt Af/nn would/md compete/vb very/ql effectively/rb with/in any/dti impurities/nns as/cs a/at scavenger/nn for/in Af/nn radicals/nns ./.
Contrary/jj to/in these/dts expectations/nns we/ppss have/hv found/vbn it/ppo impossible/jj to/to obtain/vb the/at degree/nn of/in reproducibility/nn one/pn would/md wish/vb ,/, even/rb with/in extensive/jj efforts/nns to/to prepare/vb especially/ql pure/jj reagents/nns ./.
We/ppss are/ber reporting/vbg these/dts investigations/nns here/rb briefly/rb because/rb of/in their/pp$ relevancy/nn to/in problems/nns of/in the/at study/nn of/in apparently/rb simple/jj exchange/nn reactions/nns of/in chlorine/nn and/cc because/cs the/at results/nns furnish/vb some/dti information/nn on/in the/at activation/nn energy/nn for/in abstraction/nn of/in chlorine/nn atoms/nns from/in carbon/nn tetrachloride/nn ./.



Experimental/jj-hl 
reagents/nns ./.

--/-- Matheson/np highest/jjt purity/nn tank/nn chlorine/nn was/bedz passed/vbn through/in a/at tube/nn of/in resublimed/vbn Af/nn into/in an/at evacuated/vbn Pyrex/np system/nn where/wrb it/pps was/bedz condensed/vbn with/in liquid/jj air/nn ./.
It/pps was/bedz then/rb distilled/vbn at/in least/ap three/cd times/nns from/in a/at trap/nn at/in -78-degrees/nns to/in a/at liquid/jj air/nn trap/nn with/in only/rb a/at small/jj middle/nn fraction/nn being/beg retained/vbn in/in each/dt distillation/nn ./.
The/at purified/vbn product/nn was/bedz stored/vbn at/in -78-degrees/nns in/in a/at tube/nn equipped/vbn with/in a/at break/nn seal/nn ./.


	Of/in several/ap methods/nns employed/vbn for/in tagging/vbg chlorine/nn with/in radiochlorine/nn ,/, the/at exchange/nn of/in inactive/jj chlorine/nn with/in tagged/vbn aluminum/nn chloride/nn at/in room/nn temperature/nn was/bedz found/vbn to/to be/be the/at most/ql satisfactory/jj ./.
To/to prepare/vb the/at latter/ap ,/, silver/nn chloride/nn was/bedz precipitated/vbn from/in a/at solution/nn containing/vbg Af/nn obtained/vbn from/in the/at Oak/nn-tl Ridge/nn-tl National/jj-tl Laboratory/nn-tl ./.
The/at silver/nn chloride/nn was/bedz fused/vbn under/in vacuum/nn in/in the/at presence/nn of/in aluminum/nn chips/nns with/in the/at resultant/jj product/nn of/in Af/nn which/wdt was/bedz sublimed/vbn into/in a/at flask/nn on/in the/at vacuum/nn line/nn ./.
Previously/rb purified/vbn chlorine/nn was/bedz subsequently/rb admitted/vbn and/cc the/at exchange/nn was/bedz allowed/vbn to/to take/vb place/nn ./.
The/at radiochlorine/nn was/bedz stored/vbn at/in -78-degrees/nns in/in a/at tube/nn equipped/vbn with/in a/at break/nn seal/nn ./.


	Liter/nn quantities/nns of/in Mallinckrodt/np ,/, low/jj sulfur/nn ,/, reagent/nn grade/nn carbon/nn tetrachloride/nn were/bed saturated/vbn with/in Af/nn and/cc Af/nn and/cc illuminated/vbn for/in about/rb 50/cd hours/nns with/in a/at 1000/cd watt/nn tungsten/nn lamp/nn at/in a/at distance/nn of/in a/at few/ap inches/nns ./.
The/at mixture/nn was/bedz then/rb extracted/vbn with/in alkali/nn and/cc with/in water/nn following/vbg which/wdt the/at carbon/nn tetrachloride/nn was/bedz distilled/vbn on/in a/at Vigreux/np column/nn ,/, a/at 25%/nn center/nn cut/nn being/beg retained/vbn which/wdt was/bedz then/rb degassed/vbn under/in vacuum/nn in/in the/at presence/nn of/in Af/nn ./.
Purified/vbn inactive/jj chlorine/nn was/bedz then/rb added/vbn from/in one/cd of/in the/at tubes/nns described/vbn above/rb and/cc the/at mixture/nn frozen/vbn out/rp and/cc sealed/vbn off/rp in/in a/at flask/nn equipped/vbn with/in a/at break/nn seal/nn ./.
This/dt chlorine-carbon/nn tetrachloride/nn solution/nn was/bedz illuminated/vbn for/in a/at day/nn following/vbg which/wdt the/at flask/nn was/bedz resealed/vbn onto/in a/at vacuum/nn system/nn and/cc the/at excess/nn chlorine/nn distilled/vbn off/rp ./.
The/at required/vbn amount/nn of/in carbon/nn tetrachloride/nn was/bedz distilled/vbn into/in a/at series/nn of/in reaction/nn cells/nns on/in a/at manifold/nn on/in a/at vacuum/nn line/nn ./.
The/at desired/vbn amounts/nns of/in inactive/jj chlorine/nn and/cc radioactive/jj chlorine/nn were/bed likewise/rb condensed/vbn in/in these/dts cells/nns on/in the/at vacuum/nn line/nn following/vbg which/wdt they/ppss were/bed frozen/vbn down/rp and/cc the/at manifold/nn as/cs a/at whole/nn was/bedz sealed/vbn off/rp ./.
The/at contents/nns of/in the/at manifold/nn for/in liquid/jj phase/nn experiments/nns were/bed then/rb mixed/vbn by/in shaking/vbg ,/, redistributed/vbn to/in the/at reaction/nn tubes/nns ,/, frozen/vbn down/rp ,/, and/cc each/dt tube/nn was/bedz then/rb sealed/vbn off/rp ./.
The/at reactants/nns for/in the/at gas/nn phase/nn experiments/nns were/bed first/rb frozen/vbn out/rp in/in a/at side-arm/nn attached/vbn to/in the/at manifold/nn and/cc then/rb allowed/vbn to/to distil/vb slowly/rb into/in the/at manifold/nn of/in pre-cooled/jj reaction/nn cells/nns before/cs sealing/vbg off/rp ./.
This/dt method/nn in/in general/jj solved/vbd the/at problem/nn of/in obtaining/vbg fairly/ql equal/jj concentrations/nns of/in reactants/nns in/in each/dt of/in the/at six/cd cells/nns from/in a/at set/nn ./.
Reaction/nn-hl conditions/nns-hl and/cc-hl analysis/nn-hl ./.-hl

--/-- The/at samples/nns for/in liquid/jj phase/nn thermal/jj reaction/nn studies/nns were/bed prepared/vbn in/in Pyrex/np capillary/nn tubing/nn 2.5/cd mm./nns i.d./nn and/cc about/rb 15/cd cm./nns long/jj ./.
In/in a/at few/ap experiments/nns the/at tubes/nns were/bed made/vbn from/in standard/jj 6/cd mm./nn i.d./nn Pyrex/np tubing/nn of/in 1/cd mm./nn wall/nn thickness/nn ./.
Both/abx types/nns of/in tube/nn withstood/vbd the/at pressure/nn of/in approximately/rb 20/cd atmospheres/nns exerted/vbn by/in the/at carbon/nn tetrachloride/nn at/in 220-degrees/nns ./.
The/at photochemical/jj reaction/nn cells/nns consisted/vbd of/in 10/cd mm./nn i.d./nn Pyrex/np tubing/nn ,/, 5.5/cd cm./nn long/jj ,/, diffraction/nn effects/nns being/beg minimized/vbn by/in the/at fact/nn that/cs the/at light/nn passed/vbd through/in only/ap liquid-glass/nn interfaces/nns and/cc not/* gas-glass/nn interfaces/nns ./.
These/dts cells/nns were/bed used/vbn rather/rb than/in square/jj Pyrex/np tubing/nn because/rb of/in the/at tendency/nn of/in the/at latter/ap to/to shatter/vb when/wrb thawing/vbg frozen/vbn carbon/nn tetrachloride/nn ./.
The/at round/jj cells/nns were/bed reproducibly/rb positioned/vbn in/in the/at light/nn beam/nn which/wdt entered/vbd the/at thermostated/jj mineral/nn oil-bath/nn through/in a/at window/nn ./.
Two/cd types/nns of/in light/nn source/nn were/bed used/vbn ,/, a/at thousand/cd watt/nn projection/nn lamp/nn and/cc an/at AH6/nn high/jj pressure/nn mercury/nn arc/nn ./.
The/at light/nn was/bedz filtered/vbn by/in the/at soft/jj glass/nn window/nn of/in the/at thermostat/nn thus/rb ensuring/vbg that/cs only/ap light/nn absorbed/vbn by/in the/at chlorine/nn and/cc not/* by/in the/at carbon/nn tetrachloride/nn could/md enter/vb the/at reaction/nn cell/nn ./.
Relative/jj incident/jj light/nn intensities/nns were/bed measured/vbn with/in a/at thermopile/nn potentiometer/nn system/nn ./.
Changes/nns of/in intensity/nn on/in the/at cell/nn were/bed achieved/vbn by/in use/nn of/in a/at wire/nn screen/nn and/cc by/in varying/vbg the/at distance/nn of/in the/at light/nn source/nn from/in the/at cell/nn ./.


	Following/vbg reaction/nn the/at cells/nns were/bed scratched/vbn with/in a/at file/nn and/cc opened/vbn under/in a/at 20%/nn aqueous/jj sodium/nn iodide/nn solution/nn ./.
Carrier/nn Af/nn was/bedz added/vbn and/cc the/at aqueous/jj and/cc organic/jj phases/nns were/bed separated/vbn (/( cells/nns containing/vbg gaseous/jj reactants/nns were/bed immersed/vbn in/in liquid/jj air/nn before/cs opening/vbg under/in sodium/nn iodide/nn )/) ./.
After/in titration/nn of/in the/at liberated/vbn Af/nn with/in Af/nn ,/, aliquots/nns of/in the/at aqueous/jj and/cc of/in the/at organic/jj phase/nn were/bed counted/vbn in/in a/at solution-type/jj Geiger/np tube/nn ./.
In/in the/at liquid/jj phase/nn runs/nns the/at amount/nn of/in carbon/nn tetrachloride/nn in/in each/dt reaction/nn tube/nn was/bedz determined/vbn by/in weighing/vbg the/at tube/nn before/cs opening/vbg and/cc weighing/vbg the/at fragments/nns after/cs emptying/vbg ./.
The/at fraction/nn of/in exchange/nn was/bedz determined/vbn as/cs the/at ratio/nn of/in the/at counts/nns //in minute/nn observed/vbn in/in the/at carbon/nn tetrachloride/nn to/in the/at counts/nns //in minute/nn calculated/vbn for/in the/at carbon/nn tetrachloride/nn fractions/nns for/in equilibrium/nn distribution/nn of/in the/at activity/nn between/in the/at chlorine/nn and/cc carbon/nn tetrachloride/nn ,/, empirically/rb determined/vbn correction/nn being/beg made/vbn for/in the/at difference/nn in/in counting/vbg efficiency/nn of/in Af/nn in/in Af/nn and/cc Af/nn ./.



Results/nns-hl 
the/at-hl thermal/jj-hl reaction/nn-hl ./.-hl

--/-- In/in studying/vbg the/at liquid/jj phase/nn thermal/jj reaction/nn ,/, some/rb 70/cd tubes/nns from/in 12/cd different/jj manifold/nn fillings/nns were/bed prepared/vbn and/cc analyzed/vbn ./.
Experiments/nns were/bed done/vbn at/in 180/cd ,/, 200/cd ,/, 210/cd ,/, and/cc 220-degrees/nns ./.
Following/vbg observation/nn of/in the/at fact/nn that/cs the/at reaction/nn rates/nns of/in supposedly/rb identical/jj reaction/nn mixtures/nns prepared/vbn on/in the/at same/ap filling/vbg manifold/nn and/cc exposed/vbn under/in identical/jj conditions/nns often/rb differed/vbd by/in several/ap hundred/cd per/in cent/nn ,/, a/at systematic/jj series/nn of/in experiments/nns was/bedz undertaken/vbn to/to see/vb whether/cs the/at difficulty/nn could/md be/be ascribed/vbn to/in the/at method/nn of/in preparing/vbg the/at chlorine/nn ,/, to/in the/at effects/nns of/in oxygen/nn or/cc moisture/nn or/cc to/in the/at effect/nn of/in surface/nn to/in volume/nn ratio/nn in/in the/at reaction/nn tubes/nns ./.
In/in addition/nn to/in the/at method/nn described/vbn in/in the/at section/nn above/rb ,/, chlorine/nn and/cc radiochlorine/nn were/bed prepared/vbn by/in the/at electrolysis/nn of/in a/at Af/nn eutectic/nn on/in the/at vacuum/nn line/nn ,/, and/cc by/in exchange/nn of/in Af/nn with/in molten/jj Af/nn ./.
Calcium/nn hydride/nn was/bedz substituted/vbn for/in Af/nn as/cs a/at drying/vbg agent/nn for/in carbon/nn tetrachloride/nn ./.
No/at correlation/nn between/in these/dts variables/nns and/cc the/at irreproducibility/nn of/in the/at results/nns was/bedz found/vbn ./.


	The/at reaction/nn rates/nns observed/vbn at/in 200-degrees/nns ranged/vbd from/in Af/nn of/in the/at chlorine/nn exchanged/vbn per/in hour/nn to/in 0.7/cd exchanged/vbn per/in hour/nn ./.
In/in most/ap cases/nns the/at chlorine/nn concentration/nn was/bedz about/rb Af/nn ./.
Sets/nns of/in reaction/nn tubes/nns containing/vbg 0.2/cd of/in an/at atmosphere/nn of/in added/vbn oxygen/nn in/in one/cd case/nn and/cc added/vbn moisture/nn in/in another/dt ,/, both/abx gave/vbd reaction/nn rates/nns in/in the/at range/nn of/in 0.1/cd to/in 0.4/cd of/in the/at chlorine/nn exchanged/vbn per/in hour/nn ./.
No/at detectable/jj reaction/nn was/bedz found/vbn at/in room/nn temperature/nn for/in reaction/nn mixtures/nns allowed/vbn to/to stand/vb up/rp to/in 5/cd hours/nns ./.
The/at-hl liquid/jj-hl phase/nn-hl photochemical/jj-hl reaction/nn-hl ./.-hl

The/at liquid/jj phase/nn photochemical/jj exchange/nn between/in chlorine/nn and/cc carbon/nn tetrachloride/nn was/bedz more/ql reproducible/jj than/cs the/at thermal/jj exchange/nn ,/, although/cs still/rb erratic/jj ./.
The/at improvement/nn was/bedz most/ql noticeable/jj in/in the/at greater/jjr consistency/nn among/in reaction/nn cells/nns prepared/vbn as/cs a/at group/nn on/in the/at same/ap manifold/nn ./.
Rather/ql large/jj differences/nns were/bed still/rb found/vbn between/in reaction/nn cells/nns from/in different/jj manifold/nn fillings/nns ./.
Some/rb 80/cd reaction/nn tubes/nns from/in 13/cd manifold/nn fillings/nns were/bed illuminated/vbn in/in the/at temperature/nn range/nn from/in 40/cd to/in 85-degrees/nns in/in a/at further/jjr endeavor/nn to/to determine/vb the/at cause/nn of/in the/at irreproducibility/nn and/cc to/to obtain/vb information/nn on/in the/at activation/nn energy/nn and/cc the/at effect/nn of/in light/nn intensity/nn ./.
In/in all/abn cases/nns there/ex was/bedz readily/rb measurable/jj exchange/nn after/in as/ql little/ap as/cs one/cd hour/nn of/in illumination/nn ./.
By/in comparing/vbg reaction/nn cells/nns sealed/vbn from/in the/at same/ap manifold/nn temperature/nn dependency/nn corresponding/vbg to/in activation/nn energies/nns ranging/vbg from/in 11/cd to/in 18/cd Af/nn was/bedz observed/vbn while/cs dependence/nn on/in the/at first/od power/nn of/in the/at light/nn intensity/nn seemed/vbd to/to be/be indicated/vbn in/in most/ap cases/nns ./.


	It/pps was/bedz possible/jj to/to make/vb estimates/nns of/in the/at quantum/nn yield/nn by/in observing/vbg the/at extent/nn of/in reduction/nn of/in a/at uranyl/nn oxalate/nn actinometer/nn solution/nn illuminated/vbn for/in a/at known/vbn time/nn in/in a/at typical/jj reaction/nn cell/nn and/cc making/vbg appropriate/jj conversions/nns based/vbn on/in the/at differences/nns in/in the/at absorption/nn spectra/nns of/in uranyl/nn oxalate/nn and/cc of/in chlorine/nn ,/, and/cc considering/in the/at spectral/jj distribution/nn of/in the/at light/nn source/nn ./.
These/dts estimates/nns indicated/vbd that/cs the/at quantum/nn yield/nn for/in the/at exchange/nn of/in chlorine/nn with/in liquid/jj carbon/nn tetrachloride/nn at/in 65-degrees/nns is/bez of/in the/at order/nn of/in magnitude/nn of/in unity/nn ./.


	When/wrb typical/jj reaction/nn cells/nns to/in which/wdt 0.3/cd of/in an/at atmosphere/nn of/in oxygen/nn had/hvd been/ben added/vbn were/bed illuminated/vbn ,/, chlorine/nn and/cc phosgene/nn were/bed produced/vbn ./.
Exchange/nn was/bedz also/rb observed/vbn in/in these/dts cells/nns ,/, which/wdt had/hvd chlorine/nn present/rb at/in Af/nn ./.
The/at-hl photochemical/jj-hl exchange/nn-hl in/in-hl the/at-hl gas/nn-hl phase/nn-hl ./.-hl

--/-- Although/cs there/ex was/bedz some/dti variation/nn in/in results/nns which/wdt must/md be/be attributed/vbn either/cc to/in trace/jj impurities/nns or/cc to/in variation/nn in/in wall/nn effects/nns ,/, the/at photochemical/jj exchange/nn in/in the/at gas/nn phase/nn was/bedz sufficiently/ql reproducible/jj so/cs that/cs it/pps seemed/vbd meaningful/jj to/to compare/vb the/at reaction/nn rates/nns in/in different/jj series/nns of/in reaction/nn tubes/nns for/in the/at purpose/nn of/in obtaining/vbg information/nn on/in the/at effect/nn of/in chlorine/nn concentration/nn and/cc of/in carbon/nn tetrachloride/nn concentration/nn on/in the/at reaction/nn rate/nn ./.
Data/nns on/in such/jj comparisons/nns together/rb with/in data/nns on/in the/at effect/nn of/in light/nn intensity/nn are/ber given/vbn in/in Table/nn-tl 1/cd-tl ./.
,/, 

	In/in series/nn 1/cd ,/, the/at relative/jj light/nn intensity/nn was/bedz varied/vbn by/in varying/vbg the/at distance/nn of/in the/at lamp/nn from/in the/at reaction/nn cell/nn over/in the/at range/nn from/in 14.7/cd to/in 29.2/cd cm./nns ./.
The/at last/ap column/nn shows/vbz the/at rate/nn of/in exchange/nn that/wps would/md have/hv been/ben observed/vbn at/in a/at relative/jj intensity/nn of/in 4/cd (/( 14.7/cd cm./nns distance/nn )/) calculated/vbn on/in the/at assumptions/nns that/cs the/at incident/jj light/nn intensity/nn is/bez inversely/rb proportional/jj to/in the/at square/nn of/in the/at distance/nn of/in the/at lamp/nn from/in the/at cell/nn and/cc that/cs the/at rate/nn is/bez directly/rb proportional/jj to/in the/at incident/jj light/nn intensity/nn ./.
Direct/jj proportionality/nn of/in the/at rate/nn to/in the/at incident/jj intensity/nn has/hvz also/rb been/ben assumed/vbn in/in obtaining/vbg the/at value/nn in/in the/at last/ap column/nn for/in the/at fourth/od sample/nn of/in series/nn 2/cd ,/, where/wrb the/at light/nn intensity/nn was/bedz reduced/vbn by/in use/nn of/in a/at screen/nn ./.