Broadband 308 nm vibrational Raman spectroscopy of gaseous species using a potassium hydrogen phthalate liquid filter and polarization fluorescence suppression

Abstract

Broadband XeCl excimer lasers operating at 308 nm are not currently used in the field of gas phase vibrational Raman spectroscopy (VRS). An explanation as to why alternative wavelengths, and in particular tuneable, narrowband lasers are currently preferred for gas phase VRS is presented in addition to demonstrating a setup which makes the XeCl laser a viable alternative when considering excitation sources for VRS. A solution of potassium hydrogen phthalate is shown to be a practical low-pass liquid filter and to reduce substantially the effects of Rayleigh scattering on collected Raman spectra. The use of a commercial beam polarizer is also shown to be effective in suppressing background fluorescence that otherwise necessitates the use of expensive tuneable, narrowband lasers when performing VRS with sources of background fluorescence. Finally, an unconventional excitation beam arrangement is shown to produce viable Raman spectra from which species concentrations and distributions can be determined.

Chemical Composition Monitoring in a Batch Distillation Process Using Raman Spectroscopy

“…However, for the sake of completeness, we note that, in practical systems, care must be taken because laser-induced fluorescence emission from impurities or aromatic components can cause interference with the Raman signal. Such fluorescence interference can either be avoided using laser sources in the red and near-infrared spectral ranges, taking a loss in signal intensity according to the lower scattering cross section, or be corrected for using a polarization-resolved detection scheme that takes advantage of the different polarization properties of fluorescence emission and Raman scattering. , The latter option, however, might not be a suitable generic solution to the problem, as the Raman signals generated in liquids can be depolarized to a certain extent as well …”

“…Such fluorescence interference can either be avoided using laser sources in the red and near-infrared spectral ranges, Industrial & Engineering Chemistry Research ARTICLE taking a loss in signal intensity according to the lower scattering cross section, 16 or be corrected for using a polarization-resolved detection scheme that takes advantage of the different polarization properties of fluorescence emission and Raman scattering. 25,26 The latter option, however, might not be a suitable generic solution to the problem, as the Raman signals generated in liquids can be depolarized to a certain extent as well. 27 Future work in our laboratory will focus on inline measurements combined with real-time data analysis.…”

Natural Gas Analysis Using Polarized Raman Spectroscopy

“…One of the advantages of Raman spectroscopy over other types of vibrational spectroscopy is the possibility of polarization measurements. Using this method, it is possible to determine the symmetry of vibrations, understand the orientation of molecules (freely oriented or adsorbed on the surface), discriminate enantiomers in chiral media, and suppress background and fluorescence interferences in spectra. − The basis of this approach is as follows. Raman spectra consist of isotropic ( I i ) and anisotropic ( I a ) parts.…”

Dual-Wavelength Raman Spectroscopy Approach for Studying Fluid-Phase Equilibria Using a Single Laser

“…In such situations the polarization-resolved Raman scattering is advantageous in gases as well. 12,13 To summarize, a setup for Raman scattering in two-phase fluid mixture systems employing a dual-wavelength laser source for excitation has been introduced. By using the strong beam from a frequency-doubled Nd:YAG laser for generating Raman signals in the vapor phase, the gas composition can be determined.…”