INFRARED INTENSITIES OF LIQUIDS .18. ACCURATE OPTICAL-CONSTANTS AND MOLAR ABSORPTION-COEFFICIENTS BETWEEN 6500 AND 800 CM(-1) OF DICHLOROMETHANE AT 25-DEGREES-C, FROM SPECTRA RECORDED IN SEVERAL LABORATORIES

This is the last of four papers that present the detailed measurements and results that led to the acceptance by the International Union of Pure and Applied Chemistry of Secondary Infrared Absorption Intensity Standards for liquids. In this paper accurate infrared absorption inte nsities of liquid dichloromethane at 25 degrees C are presented. The a ccuracy was estimated from the +/-1.5% average agreement of integrated intensities over specific wavenumber ranges between spectra measured by five spectroscopists in four laboratories. The use of data from dif ferent instruments in different laboratories has significantly include d the effect of systematic instrumental errors. The spectra from the d ifferent spectroscopists have been averaged, unweighted, to give inten sity spectra of dichloromethane that are presented as the best availab le. The results obtained agree with the only measurements that have be en made against a primary standard, the estimated accuracy of which is about 5.5%. The spectra of the molar absorption coefficient and or th e real and imaginary refractive indices are reported as tables and gra phs between 6500 and 800 cm(-1). Also reported are the peak heights an d the areas under band groups in the molar absorption coefficient and imaginary refractive index spectra. The imaginary refractive index, k( (v) over tilde), and molar absorption coefficient, E(m)((v) over tilde ), values are believed to be accurate to an average +/-2.3% over the 3 6 measured bands. The baseline k((v) over tilde) values are believed t o be accurate to similar to 8% below 6000 cm(-1), similar to 1% below 4500 cm(-1), and similar to 25% above 6000 cm(-1), where the absorptio n is extremely weak. The areas under band groups in the k((v) over til de) and E(m)((v) over tilde) spectra are believed to be accurate to 1. 5% averaged over the 15 measured band groups and to 1.0% over the 10 b and groups below 3600 cm(-1). The real refractive index, n((v) over ti lde), values are believed to be accurate to 0.2%.