Polarized Raman Spectra of α Quartz

Abstract

The purpose of this experiment was to observe the Raman shift to assign the symmetry character of the obtained vibrational modes of α-quartz (which has 9 atom per unit cell) using the selection rules for Raman Effect. We observed the Raman spectra varying the polarization of the incoming beam and the orientation of the crystal. And we used monochromatic radiation of argon laser of wavelength 540 nm for our Raman spectroscopy. We observed the intensity of light rotating the polarizer to vertical position from its horizontal position with respect to the plane of the optical table where the laser is placed and measured the Raman spectra over an energy from 50 to 1250 cm -1 using the laser power of 1W and an acquisition time of 10 sec. averaging over 2 acquisitions. From our experiment we can see that here is 4symmetry for A 1 which is predicted on our vibrational modes. However for E symmetry mode we have observed 14 vibrational modes but as E is doubly degenerate there should be 16 vibrational modes on the Raman active modes in the α quartz, as we can see that there are two vibration missing ,it happens may be due to noise on the surroundings. We got different peaks due to the different intensities and the different orientation of the laser beam hitting the sample on different angle. The different intensities of the peaks for the different orientation might be due to the laser beam hitting the samples at different angles due to differences in the orientation of the surfaces. We also found that the biggest amount of the re-radiated light was vibrating horizontally, i.e. in the same direction as the laser beam hitting the sample.