ASTM E1840-96(2014)

4.1 Wavenumber calibration is an important part of Raman analysis. The calibration of a Raman spectrometer is performed or checked frequently in the course of normal operation and even more often when working at high resolution. To date, the most common source of wavenumber values is either emission lines from low-pressure discharge lamps (for example, mercury, argon, or neon) or from the non-lasing plasma lines of the laser. There are several good compilations of these well-established values (1-8).³ The disadvantages of using emission lines are that it can be difficult to align lamps properly in the sample position and the laser wavelength must be known accurately. With argon, krypton, and other ion lasers commonly used for Raman the latter is not a problem because lasing wavelengths are well known. With the advent of diode lasers and other wavelength-tunable lasers, it is now often the case that the exact laser wavelength is not known and may be difficult or time-consuming to determine. In these situations it is more convenient to use samples of known relative wavenumber shift for calibration. Unfortunately, accurate wavenumber shifts have been established for only a few chemicals. This guide provides the Raman spectroscopist with average shift values determined in seven laboratories for seven pure compounds and one liquid mixture.

1.1 This guide covers Raman shift values for common liquid and solid chemicals that can be used for wavenumber calibration of Raman spectrometers. The guide does not include procedures for calibrating Raman instruments. Instead, this guide provides reliable Raman shift values that can be used as a complement to low-pressure arc lamp emission lines which have been established with a high degree of accuracy and precision.

1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.3 Some of the chemicals specified in this guide may be hazardous. It is the responsibility of the user of this guide to consult material safety data sheets and other pertinent information to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to their use.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.