Topics in..
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Chemical Instrumentation Edited by GALEN W . EWING, Seton Hall University, So. O r a n g e , N. J. 07079
The secotid i)igilnb, Ine., inslmment is the FTRlG spedromeler shown schematically in Figwe ::!I The . optical system may be e v a c ~ ~ a t e or d purged. Wavelength range: 10 em-' t o 200 am-', or 3 cm-' t o 650 cm-I optiond. Reoli~bion: 0 . 5 cm-I (operator variable) is standard, 0.1 cm-' is optiond. Interehangenhle, st,relched dielertrir heamspli1tet.s are used. A prerisiot> steppittg motw provides 5-p steps for the rnimor motion. Each step cat, ire adjusted to 0.3, 1, 2, or 4 ser m m inal dwell time. The source is a highpmswre mcrcwy arc. 1)etertut.s x e the ( h l u y rell 01.TGS detector w e d with ihe FTS-14 system. Cryogenic detertors ran he in~ol.po1.ated. The detet,lor signal is ol.ocesscd bv a stable :&MI linear lack-in amplifier i,11118d lo the chopper heqnmry. The inierferograrn produced in this m m -
T h e s e articles are intended to serve the readers O J T H IJOURNAL S b!, cnlliny atlention to new developments i n the theory, design, or availability of chemical laboratory instrumentation, or by presenting useful insights and explanations of topics that are of practical importance lo those who use, GT teach the use of, niodern instrumentation and instrumental techniques. The edilor invites correspondence from prospective contributors
LI. Fourier Transform Spectrometers.
Part Three (Continued) M. J. D. LOW, Deporfmenf o f Chemistry, New York Universify, New York, N . Y. 10453 Block Engineering, Inc. The Digilah, Inc. subsidiary of Block Engineering, In,:., has iwo instrtments capable of p~.odocingfm-ildmrod spectm. One of these, theFTS-1% has already been described. Although p ~ . i n a i p d yintended for the fiugeqwinl. range, Model 206 of ihe FTS-14 e a be ~ modifiecl. ~ The design tolerance of n Miehelsun interferometer set up t o measure spectra in the mid-infrared legion exceeds that 1.eqnised for the far-infrared. Only a few simple alterations are, therefore, lierewary to modify the FTS-14 for inl;infrared entmsion t o 1000 p (10 m - ' ) . These include replacing lhc glower somrc with n high-prcsmr'o merrnry lamp whose ernissivity beyond 100 nn-' is much soperior to that of a glower. The 1iesmsplitte1.s for this region are slwirhed h l y l ~ rpolyester films of vsriona lhirk~\essra. The same type of iriglyciue s d f a l e (TGS) deieclor, having good sensitivily and flat r.esponse iu the f n ~ i n f r a r e d m , u he w e d . The far-iufrnred physical cotrversion is ~.apidlym d simply dove, with w n e q d l y simple preparkaged sdtware rllange in ihe 1)igilab datn system, the changeover is completed in less thau an how. The con-
version is done h y mentir of n "ro~tvel.sion kit," shown in Figure 38. The resuI( is :I rompoter-controlled fn~.-infmretlsperit.ometer; sce the e d i w description of lhe FTS-I4 system. Moving Mirier
Fixed Mirror
Figure 39. diogrom
Digilab
Model
FTS-16
opficol
Grubb Porronr, Lid. Grul,l, I'a~sol~splncloces two iltstlnmct>tswhich are marketed in the IJniled Sisies hy Edwilt Iudttsi~.iesC O I ~ O I R ~ ~ O N . The IS3 speelmmeter complete with elect ~ m ~ i and c s ennsole is shuwl>i l l Figure 42. Opt.irs1 dixgnms for the IS3 m e slir,wn it, Figwe 43. The r w g e of the IS3is 1 0 4 7 5 Figure 40. trometei
Figure 38. Kit far conversion of Digilab FTS-14 ryrtem for for-infrared operation. A highpressure mercury lamp, chopper, Mylor fllm beomrplitfer, and TGS detector ore used.
Beam S p l i t t e r
--0
9 60 70 aa FRIOYTNC" INWAVENYMSERS
Figure41.
(Contiruin1 on page A41fi)
FTS-16/Digilab for-infrared rpec-
rn
lm
!to
,la
724
0.i
550
1m
rio
,m
iw
ma
Wafervapor spectrum, meorwed by Digilob FTS-16 spectrometer
Volume 47, Number 6, June 1970
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A41 5
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rm-1 if ndiarr~oltddetcrtul.wi~ldow is wed, and 10-200 cm-' if a quarta window is used. The ~.esolut,imlis variable to 0.1 cm-1 maximum. The movi!!g mirror is nerurntely mounted O H n g l w s blork m d moved in diswete steps of 3 p path diffe1,enee. These step* can be nrrauged by the opentor to occur at time intervals of O..?, 1, '2, 4 sec or longer. Polyethyleue teiephthslate beamsplitters in a mnge of thicknesses are used. 1)iReretrt sample
,.*
,.~"....."
~i~~~~ 43.
Opticcl diogrom for 153 rpectrom-
eter
rhembel.~are available (see Fig. 4 3 ) . The smnll-rhnmher SC1 will arcommodnte 10em gay cells ar rnell as other cells. A rotary system enal,les up t ~ six , solid samples l o be d a r e d in the snmule rhamber beiore evxcnnting. The Ixl.ge-rhnrnhel. SC' nrrommndaler larger attachments and hesting or rooling devices. The IS3 electm>icsinclude a lork-in amplifier liuled t o the 1G-Z!;3 Hz or 20 IIz rhopper, all A/I) cuwerter, a p n k e drive w i l for drivilig t,he moviug mitmr system n d A/[) ronverter, and an Addo papep tnpe punch. The necessary transforms are carried ont hy an dl-line camputel.. Accessories xvailnhle for the IS3 include R 1x13 reeo~der,F i r m i gauge, a micros n m p l i ~ ~accessory g shown i l l Figure 44, and cell kits s w h ns thal show\ in Fieme 45.
The s e r o ~ itt4rinnent l is the Mark I1 Figure 42. Gwbb Po,ronr 153 for-infrared wecfrometer
A41 6 / Journol of Chemical Education
Chemical instrumentation
which pn,duces disrl.ele changes of 1,8111 differencc.; 111 5 r . These steps can 1,c n ~ . ~ m > g81 e diutervals of 0.5, 1, 2, or 4 set., as reqlired. Stretched dielectric beanspliltws such as t h w e shown in Figwc 4!i are wed. The s o w c e is n high-pl.essme mercury vapor lamp. Thc eleclrw>irsincludc power supplies, s high-gni~~ lurk-in amplifier, nn A/]) cmwerler, n l d all osaillabor far operating the m i m n drive triggering tho A l l ) converler. An oncoding sel.i$iser i s thett !wed to drive R paper-tape punch. I h t a processiug is mrried out by an off-lille cornputor. Figure 46.
"(:ul,rn it~lerfe~.cmirlri. d w i g ~ i r dii,y the N;LI i m d I'hysiw I.:~lm~nlwy a1 Toddinglwt, l h g l m ~ l ,%MI dcv~lopedl>y G r u l h I'arsm~s. An opt i d di;qrarn of the M u k 11 i.; rhow>ci t ) I'ipve4fi. Figwe 47 shawi Ihe iwtnln,e~rl phw elert~.onics,and nn "erplderl" view of ihc intcrferomeler is given i u Figwc 48. The 1lat.k I1 rovers the 10-200 rrn-' t m g e , using n (:
