Datensatz

Zusammenfassung

Stable isotopes are used in ecology to track and disentangle different processes and pathways. Especially for
studies focused on the gas exchange of plants, sensing
techniques that offer oxygen (O2) and carbon dioxide (CO2)
sensitivity with isotopic discrimination are highly sought after.
Addressing this challenge, fiber-enhanced Raman gas spectroscopy
is introduced as a fast optical technique directly combining
13CO2 and 12CO2 as well as 18O2 and 16O2 measurements in one
instrument. We demonstrate how a new type of optical hollowcore
fiber, the so-called revolver fiber, is utilized for enhanced
Raman gas sensing. Carbon dioxide and oxygen isotopologues
were measured at concentrations expected when using 13C- and
18O-labeled gases in plant experiments. Limits of detection have
been determined to be 25 ppm for CO2 and 150 ppm for O2. The combination of measurements with different integration
times allows the creation of highly resolved broadband spectra. With the help of calculations based on density functional theory,
the line at 1512 cm−1 occurring in the oxygen spectrum is assigned to 18O16O. The relative abundances of the isotopologues
18O16O and nitrogen 15N14N were in good agreement with typical values. For CO2, fiber-enhanced Raman spectra show the
Fermi diad and hotbands of 12C16O2, 13C16O2, and 12C18O16O. Several weak lines were observed, and the line at 1426 cm−1 was
identified as originating from the (0 4 0 2) → (0 2 0 2) transition of 12C16O2. With the demonstrated sensitivity and
discriminatory power, fiber-enhanced Raman spectroscopy is a possible alternative means to investigate plant metabolism,
directly combining 13CO2 and 12CO2 measurements with 18O2 and 16O2 measurements in one instrument. The presented
method thus has large potential for basic analytical investigations as well as for applications in the environmental sciences.