Calibrating wavelengths in the region from 0.6 to 2.6 microns

Th e wa ve lengths of twent y absorption bands ha\'e been measured o n a grating bpectrometer in the region from 0.6 to 2.6 mi cron s.Algo .se ver a l e mi s~i on lines of kr.vpton hay '! been meas ured in the near infrared region .Th e purpose of t his investiga ti on was to mak e avai lable additional calibration poin ts for pris m instrume nts.The bands whi ch \\'ere selected fo r calibration are part s of t'he absorptio n s pectra of didymium glass, car bon disulfid e, 1,2,4-trichl orobenze ne, ca rbon disulfide , and polys ty re ne.Five grap hs of th e measured spectra a re in cluded , and the calibrated wavele ngt h, are mark E'd on t he band., in order to fa cilitate identification .In o rd er to calibrate prism instrum en ts ad equately, many abso rp tion.bands and emission lin es of accuratcl. wavelength s are n eeded .This is e pecially so in t he wavelength r egion b etween 0.6 to 2.6 J.l. , wh ere the wave numb er span is 16,000 cm -l .The purpose of thi s inves tigation was to provid e add itional calibration poin ts in th e near infrared region.for use with prism ins truments.Previou sly , th e problem of obtaining cal ibration points in th e inhal'ed region h as been studied by Oetjen, Chao-Lou Kao , and Randal!.l : More re cently, Plyler and Peters 2 have added ealibration points co vei:ing th e ("egion from 2 to 25 J.l . .There are still several gaps wh er e furtbcl' calibration points woulel be high l ~T desirable , in addition to t h e combined results giv en in th e articl es cit.eel in footnotes 1 and 2.The calibration of oth er points in th (' , ncar infrared r egion from th e visibl e to 2.5 J.l. h as been neglected b ecause no fundamental vibrational ab sorption band s h ave wavelength s less than 2.5 J.l . .For thi s reaso n, most observations commence at 2 J.l.. Re centl~', th e importance of combination and h armonic bands has h een l'ecognilleci in the anal~' si s of spe ctra, and m easm ements arc now being mad e at wav el engths less than 2 J.l.. ~Jore accurat e calibratin g wavek ngth s are n ecessary in order to fullv uLili ze G h e hi gh sensitivity of inst ruments which a rc eq uipp ed with lead sulfid e (PbS ) cell s.The leael sulfid e cell has been found to be very ens itive JOY th e d etection of radiant energy from 0:6 to 2.6 J.l .and thu s allows a much greatm' accurac.vand high er l'esolu lion than h it herto possible fOl' prism instruments.Th e wavelength s listed in the presen t stud.vshould assist in rel ieving this sit uation.Th e absorpLion bands selected for calibra tion \\"ere m easured on a high -dispersion grat ing sp ectrometer.Th csp ectrometcr hasa l 5,000-li ne-per-ineh graling as th e dispersing uni t, an d th e collima ting m irror has a focal Irngth of 102 em.A lead-s ulfid e pholocondu cting cell detects the radiant enel'g, passing L hrough t]l e exit slit of th e specLI•ometer.A more complete description of th e gratin g sp eetrometet' h as b een given in a previolls pap er and will not be repeated h e1'e.3