Table I I I . Spectral Regions Covered with 2.532-μπι Sampling Interval (*4 Sampling Rate)

Region cm -1 A

1 0-1,975 — 5 μ

6 7 8 9

11,851-9,876 11,851-13,826 15,802-13,826 15,802-17,777

8,438-10,125 8,438-7,233 6,328-7,233 6,328-5,625

15 16

27,653-29,628 31,605-29,628

3,616-3,375 3,164-3,375

Table IV. Major Emission Lines of Cs, Rb, K, and Li in Near IR Region (Table III) A en

Cs 6 8943 11,181 6 8521 11,735

Rb 7 7947 12,583 7 7800 12,820

Κ 7 7698 12,990 7 7664 13,048

Li 8 6707 14,909

this sampling interval are listed in Table I. Regions 2-4 are aliased re­gions. Spectral information in all of these regions can be measured simul­taneously as long as aliased spectral

lines do not exactly overlap. With a sampling interval of 1.266 μηι (-ί-2 sampling rate), these four regions be­come eight regions, each covering a bandwidth of 3950 c m - 1 (see Table

II). With a 2.532-μπι sampling interval (-j-4 sampling rate), 16 regions each with a bandwidth of 1975 c m - 1 can be simultaneously covered. A partial list of the regions is presented in Table III. Thus, given a fixed number of data points that can be acquired and transformed, spectral lines of widely different wavelength can be simulta­neously measured with significantly better resolution than could be achieved if aliasing were avoided. Flame emission spectra of Cs, Rb, K, and Li were measured with our Fouri­er transform spectrometer to illustrate this point.

The emission lines of these ele­ments in the near-IR region are listed in Table IV along with the region from Table III that they fall into. Solutions containing only one element each were aspirated into an air-C2H2 flame, and the emission was measured with the interferometer by use of a silicon pho­tocell as the detector. The analog in-terferograms for the emission signal from each element are shown in Fig­ure 2. The beat patterns in the K, Rb, and Cs interferograms clearly indicate that the spectra all consist of two lines, and the frequency of beating can be related directly back to the doublet separation, the potassium doublet having the least separation. These in­terferograms were digitized with the

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778 A · ANALYTICAL CHEMISTRY, VOL. 47, NO. 8, JULY 1975

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