Factors That Affect the Accuracy of Raman Shift Measurements on Multichannel Spectrometers

Raman shift measurements have been made on cyclohexane, by using linear interpolation between bracketing neon line positions to establish Raman band wavelengths. Factors that affect the precision of these measurements have been examined in detail. These include change of slit width, grating line spacing, neon line intensity, distance of separation of neon lines, and effects of small grating movements. All these have some effect, but the last factor is particularly important. Techniques that give standard deviations of 0.03 cm −1 when measurements are made without moving the grating are degraded by about an order of magnitude when the grating is moved. This result is attributed to adventitious partitioning of signal power between adjacent detector elements. By deliberately moving the grating a small amount between otherwise replicate measurements, one can control this effect. Values for the Raman shifts for eleven cyclohexane bands, based on approximately 800 Raman spectra and an equal number of neon emission spectra, are presented. The values are compared with previous measurements. They are generally within the ±σ range of the earlier values, but the standard deviations of these results are about an order of magnitude smaller.