Research On Water Vapor Interference In Far-infrared Spectroscopy And Characterization Of Crystal Morphology By Micro-raman Spectroscopy

Infrared and Raman are both molecular spectroscopy, cooperated with each other toprovide more comprehensive information of molecular structure. They have been widely usedin medicine, materials, chemicals, petroleum, environmental protection and other fields.Water vapor absorption from the atmospheric air may severely obscure the spectroscopiccharacterization of the sample in a far infrared (FIR) spectrum. In this paper, we introduce aconcept wet and dry air spectral titration and provide a novel method to eliminate watervapor interferences under a fluctuant humidity circumstance. The scanning procedure of asample single-beam spectrum has been divided into two stages, namely dry air and wet airstages. If the relative humidity in the spectrometer at the first stage is lower than that of thebackground single-beam spectrum, the relative humidity has to be changed by a wet air blow.The reverse is also true. By this way, the effects of the dry air and the wet air at two stageswould appear to cancel each other out by signal averages. If appropriate scanning number forboth dry air and wet air stage is selected, water vapor peaks can be removed progressively andcompletely. This method was successfully applied to measure the far infrared spectrums of100%baselines, L-histidine and D-galactose.The ideal100%lines could not be obtained when the content of water vapor in thespectrometer is constant but high during the whole procedure of a far-infrared spectrumcollection. This result indicates that anomalous absorption phenomenon takes place in highrelative humidity atmosphere. In this paper，we collected100%baselines of empty opticalpath in2cm-1,4cm-1,8cm-1spectral resolution in different constant humidity. The anomalousabsorption phenomenon arised from ambient air have been observed and studied. Theanomalous absorption is significant different from that of random noise and will distort theaccuracy of the far-infrared spectra. It was found that both to decrease the water vapor contentin the spectrometer and to adopt low spectral resolution are effective methods to avoidanomalous absorption.Raman intensity is a powerful tool which contains chemical environment and physicalbehavior. Three typical morphology CaC2O4·H2O particles (A, B, C) were synthesized by two ways and measured in the range50-2000cm-1by Micro-Raman Spectroscopy. Spectroscopicbehaviour related to oxalate anion (C1-C2) lay in the (100) plane is completely differentfrom other vibrational modes in three representative particles. The (CO2-)sym (503cm-1)has significantly decreased, whereas theν(CO2-)sym (1463cm-1) dramatically increased fromA to C. Particularly, the bending vibration (503cm-1) is stronger than the stretchingvibration(1463cm-1) in crystal A. On the other hand, the relative intensity of503cm-1vs522cm-1depends on the value of m/n in hexagon crystals. It seems that the intensity of503cm1and522cm1assigned to (CO2-)sym have somewhat relationship with the (120) and (010)plane of in CaC2O4·H2O crystals. The interesting Raman performance was observed anddiscussed in the direction of crystallographic structure and growth orientation for the firsttime.