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A Handy Indicator of Resolution in Raman Spectroscopy

Volume 44, Number 8 (Oct. 1990) Page 1414-1415

Paroli, Ralph M.; Butler, Ian S.

There are now numerous spectroscopy laboratories located throughout North America and in the rest of the world in which an Instruments S. A. U-1000 Ramanor spectrometer is employed to collect Raman data. Often, these measurements involve the use of different laser lines to excite the Raman spectra. During the course of our own work over the past six years on this type of instrument, we have needed to have knowledge of the actual resolution in wavenumbers rather than simply the slit-width settings in microns for a variety of argon- and krypton-ion laser lines. To aid us in this endeavor, we have constructed the curve shown in Fig. 1 using information provided by Instruments S. A. for the dispersion of the 1.0-m double monochromator of the U-1000 spectrometer when equipped with two 1800 grooves/mm−1 holographic gratings. The equation for this curve is:

Res. = {(0.2254 − 1.436∗10−3∗λ + 3.959∗10−6∗λ2 − 5.645∗10−9∗λ3 + 4.073∗10−12∗λ4 − 1.177∗10−15∗λ5)∗μ} [1a]


μ = Res./(0.2254 − 1.436∗10−3∗λ + 3.959∗10−6∗λ2 − 5.645∗10−9∗λ3 + 4.073∗10−12∗λ4 − 1.177∗10−15∗λ5) [1b]

where the resolution is given in cm−1, λ is the wavelength in nm, and μ is the slit width in μm. The equation governs the range of the U-1000 monochromator from 300.0 to 909.1 nm. The resolutions for commonly used wavelengths, in Raman spectroscopy, are given in Table I. Furthermore, since for a given wavelength the plot of slit width vs. resolution is linear, the equations of the lines for the wavelengths shown in Table I are listed in Table II. It is hoped that this handy resolution guide will prove useful to other members of the Raman spectroscopic community.