INFRARED INTENSITIES OF LIQUIDS-XI - INFRARED REFRACTIVE-INDEXES FROM8000 TO 2 CM-1, ABSOLUTE INTEGRATED-INTENSITIES, AND DIPOLE-MOMENT DERIVATIVES OF METHANOL AT 25-DEGREES-C

This paper reports infrared absorption intensities of liquid methanol at 25-degrees-C between 8000 and 2 cm-1. Measurements were made by att enuated total reflection spectroscopy by four different workers betwee n 1984 and 1991, with the use of CIRCLE cells of two different lengths and with several different alignments of the cell in the instrument. Steps were taken to ensure that as few parameters as possible remained unchanged throughout the series of measurements, to try to reveal sys tematic errors. The reproducibility was better than +/-2.5% in regions of significant absorption. In order to allow comparison between diffe rent methods, results of all methods were converted to real and imagin ary refractive index spectra. Measurements were also made by transmiss ion spectroscopy in regions of weak absorption, with results that agre ed excellently with those from ATR. The ATR and transmission results w ere combined to give a spectrum between 7500 and 350 cm-1. This spectr um agreed excellently with literature results from 350 to 2 cm-1, and the two sets of measurements were combined to yield a spectrum from 75 00 to 2 cm-1. The imaginary refractive index was arbitrarily set to ze ro between 7500 and 8000 cm-1, where it is always less than 2 x 10(-6) , in order that the real refractive index can be calculated below 8000 cm-1 by Kramers-Kronig transform. The results are reported as graphs and as tables of the real and imaginary refractive indices between 800 0 and 2 cm-1, from which all other infrared properties of liquid metha nol can be calculated. The accuracy is estimated to be +/-3% below 500 0 cm-1 and +/-10% above 5000 cm-1 for the imaginary refractive index a nd better than +/-0.5% for the real refractive index. To obtain molecu lar information from the measurements, one calculates the imaginary mo lar polarizability spectrum, alpha''(nu) vs. nu, under the Lorentz loc al field assumption, and the area under nualpha''(nu) bands is separat ed into contributions from different vibrations under several approxim ations. Much accuracy is lost in this process. The changes of the dipo le moment during normal vibrations, and during OH, CH, and CO bond str etching and COH torsional motion, are presented.