Topic:

vibrational spectra of matrices in the gaseous phase and in matrices of inert gases

Vibrational Spectra in Gaseous Phase

Non-structural techniques include FTIR (Fourier-Transfer Infrared) spectroscopy whereby vibrational spectra emanating from gases in the gaseous phase especially the inert gases offer a preview of the molecular structure and presence of chemical bonds in the sample. There are two primary methods for studying vibrational spectra in the gaseous phase: In this work infrared (IR) spectroscopy and Raman spectroscopy are identified as the two prominent types of measurements(Jacox).

Sample Preparation: The sample is usually in the gaseous phase as a gas cell sample or a vapor phase Raman sample taken directly into the spectrometer’s path and in contact with an IR source.

Molecular Vibrations; Movement in the gaseous state is independent, thanks to the freedom offered by that state. Vibrational spectroscopy is an analytical technique which majorly targets at characterization of molecular vibrations in which atoms in a molecule vibrate around the center of gravity.

Infrared (IR) Spectroscopy:

These techniques include illumination of the sample with light of specific particular wavelengths and measuring the absorbance or scattering of the light. Molecules can only absorb corresponding frequencies of infrared radiation(Andrews).The frequencies of infrared light associated with their vibrational–rotational manifolds. Different kinds of vibratory motion include stretching, bending, rocking and so on and they have got specific vibrations(Pimental and Charles).

For instance, CO2 has different frequency absorb.

Figure 1:IR Spectrum of CO2

Raman Spectroscopy:

In Raman spectroscopy, a monochromatic light interacts with molecules and is scattered producing a spectrum. Of all the functional models, it quantifies the variation of energy of scattered light arising from molecular oscillations. Raman spectra are similar to the IR spectra, but they show information in the anti-symmetric modes and are most effective for the non-polar molecules(Perchard, Murphy and Bernstein).

Figure 2 : Raman spectrum of different state of CO2

Applications:

Ø Spectra attained from vibrational transitions in gaseous media are also applied in numerous branches of science such as chemistry, physics, and environmental science.

Ø These are useful in giving information on the chemical constitution of substances, and on the nature and course of reactions, and for analyzing the state of gaseous molecules.

Ø A notable application of molten-salt and gas-phase vibrational spectra is in meteorological analysis to evaluate the composition of the Earth’s atmosphere.

Vibrational Spectra in Inert Gas Matrices:

Solid Matrices: Inert gas matrices are employed to immobilise the molecules in a solid structure where the molecules can be embedded. Some of the most often used inert gases are argon, xenon, and helium containing noble gases primarily being a group of chemically inactive elements(Lyon et al.).

Sample Preparation:

A small amount of the target compound is placed on a reaction vessel to be subjected to the chosen inert gas at high vacuum. The mixture is then promptly frozen and collected on a metallic plate which acts as the substrate for the formation of the solid matrix.

Matrix Isolation Technique:

The matrix isolation technique can be described also as the process when the inert gas is cooled to the temperature below its boiling point and the desired molecule is then inserted in the matrix. The molecule simply becomes enclosed within he lattice structure because the solid inert gas is impermeable to the molecule(Perchard, Murphy and Bernstein).

IR Spectroscopy:

Same to the gaseous-phase IR spectroscopy, the matrix is exposed to IR radiation to carry out the analysis. Vibrational sharp peaks are noted, however, these are further apart and broader because of the matrix(Jacox).

Advantages:

Ø Remedies for a wide array of analytes which are generally reactive or short-lived at ambient environmental temperatures.

Ø Enables one to study the molecules in conditions that may be free from interfering interference from other species of molecules.

Ø Presents data regarding the impact of the matrix on the elements of molecular characteristics

REFERENCE

Andrews, LESTER. “Infrared Spectra of Free Radicals and Chemical Intermediates in Inert Matrices.” Annual Review of Physical Chemistry 22.1 (1971): 109–32. Print.

Jacox, Marilyn E. “Comparison of the Ground State Vibrational Fundamentals of Diatomic Molecules in the Gas Phase and in Inert Solid Matrices.” Journal of Molecular Spectroscopy 113.2 (1985): 286–301. Print.

Lyon, L Andrew, et al. “Raman Spectroscopy.” Analytical Chemistry 70.12 (1998): 341–62. Print.

Perchard, JP, WF Murphy, and HJ Bernstein. “Raman and Rayleigh Spectroscopy and Molecular Motions: Iii. Self-Broadening and Broadening by Inert Gases of Hydrogen Halide Gas Spectra.” Molecular Physics 23.3 (1972): 535–45. Print.

Pimental, GC, and SW Charles. “Infrared Spectral Perturbations in Matrix Experiments.” Pure and Applied Chemistry 7.1 (1963): 111–24. Print.