page_title: Geology applications of Fourier transform infrared spectroscopy
section_title: Volatiles diagnosis
hierarchical_section_title: Geology applications of Fourier transform infrared spectroscopy / Applications in geology / Volatiles diagnosis
caption_attribution_description: English: Example of an FTIR spectrum. The absorbance of some of the molecular structures shown in the spectrum: Total water at 3450cm-1, molecular water at 1630cm-1, carbon dioxide at 2350cm-1 and carbonate molecule at 1430cm-1.
context_page_description: Fourier transform infrared spectroscopy is a spectroscopic technique that has been used for analyzing the fundamental molecular structure of geological samples in recent decades. As in other infrared spectroscopy, the molecules in the sample are excited to a higher energy state due to the absorption of infrared radiation emitted from the IR source in the instrument, which results in vibrations of molecular bonds. The intrinsic physicochemical property of each particular molecule determines its corresponding IR absorbance peak, and therefore can provide characteristic fingerprints of functional groups.
  In geosciences research, FTIR is applied extensively in the following applications:
  Analysing the trace amount of water content in Nominally anhydrous minerals
  Measuring volatile inclusions in glass and minerals
  Estimating the explosion potential in volcanic setting.
  Analysing chemotaxonomy of early life on earth
  Linking biological affinities of both microfossils and macrofossils
  These applications are discussed in details in the later sections. Most of the geology applications of FTIR focus on the mid-infrared range, which is approximately 4000 to 400 cm⁻¹.
context_section_description: The most commonly investigated volatiles are water and carbon dioxide as they are the primary volatiles to drive volcanic and magmatic processes. The absorbance of total water and molecular water is approximately 3450 cm-1 and 1630 cm-1. The peak height of the absorption bands for CO₂ and CO₃²⁻ are 2350 cm⁻¹ and 1430 cm⁻¹ respectively. The phases of volatiles also give different frequency of bond stretch  and eventually produce a specific wavenumber.  For example, the band of solid and liquid CO₂ occurs in between 2336 and 2345 cm⁻¹; and the CO₂ gas phase shows two distinctive bands at 2338 cm⁻¹  and 2361 cm⁻¹. This is due to the energy difference under vibrational and rotational motion of gas molecules.
  The modified Beer-Lambert Law equation is commonly used in geoscience for converting the absorbance in the IR spectrum into the species concentration:
  Where ω is wt. % of the species of interest within the sample; A is the absorbance of the species; M is the molar mass (in g mol⁻¹); ϵ is molar absorptivity (in L mol⁻¹ cm ⁻¹); l is sample thickness (in cm); ρ is density (in g mol⁻¹)
  There are various applications of identifying the quantitative amount of volatiles by using spectroscopic technology. The following sections provide some of the examples:
caption: Example of an FTIR spectrum. The absorbance of some of the molecular structures shown in the spectrum:  Total water at 3450cm-1, molecular water at 1630cm-1, carbon dioxide at 2350cm-1 and carbonate molecule at 1430cm-1.
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