Avoiding misidentification of bands in planetary Raman spectra

Abstract

Raman spectroscopy has been identified as a powerful tool for astrobiology and remote robotic planetary exploration. It can be used to identify and characterise rock matrices, mineral inclusions and organic molecules and is demonstrably effective at identifying biomarkers, or indicators of biological activity. The ExoMars rover, jointly operated by the European and Russian Federal Space Agencies, will carry the first Raman spectrometer into space when it launches in 2018 and two further Raman instruments have recently been announced as part of the payload onboard the National Aeronautics and Space Administration's Mars 2020 rover. Each of these spectrometers however will, by necessity, have poorer resolution than the most sophisticated laboratory instruments because of mass, volume and power constraints and the space readiness of the requisite technologies. As a result, it is important to understand the minimum instrument specification required to achieve the scientific objectives of a mission, in terms of parameters such as spectral resolution and laser footprint size. This requires knowledge of the target minerals and molecules between which there may be ambiguity when identifying bands in spectra from geological samples. Here, we present spectra from a number of Mars analogue samples that include a range of such molecules, highlighting where such confusion may occur and identifying the most useful bands for differentiation. It is recommended that a Raman spectrometer achieves a resolution of at least 3 cm−1 and covers a spectral range from 100 to 4000 cm−1 in order to differentiate between all of the target molecules presented here. Copyright © 2015 John Wiley & Sons, Ltd.

Minerals and microstructure identification using Raman instruments: Evaluation of field and laboratory data in preparation for space mission

“…Examples are given here for quartz and sphalerite for which only 1 and 2 were detected respectively with the portable instrument, whereas 4 and 5 bands were respectively detected using the micro-Raman instrument. The observation of only 1 or 2 bands can complicate to a great extent the interpretation of spectra, in particular when Raman bands overlapped or appeared at identical positions for different minerals, as already discussed in Harris et al [31] According to Table 1, Raman bands with an intensity less than 10% of the intensity of the dominating Raman band are not detected with the portable instrument. The lower limit for the signal detection is decreased to 3% of the intensity of the dominating Raman band.…”

Recent advances in linear and non‐linear Raman spectroscopy. Part X

“…They presented spectra from a number of Mars analog samples that include a range of molecules, highlighting where such confusion may occur and identifying the most useful bands for differentiation. It is recommended that a Raman spectrometer should achieve a resolution of at least 3 cm −1 and covers a spectral range from 100 to 4000 cm −1 in order to differentiate between all of the target molecules presented . Jehlicka and co‐workers have evaluated portable Raman instruments with 532 and 785‐nm excitation for the identification of zeolites and beryllium containing silicates.…”

“…It is recommended that a Raman spectrometer should achieve a resolution of at least 3 cm À1 and covers a spectral range from 100 to 4000 cm À1 in order to differentiate between all of the target molecules presented. [174] Jehlicka and co-workers have evaluated portable Raman instruments with 532 and 785-nm excitation for the identification of zeolites and beryllium containing silicates. To their knowledge this is the first time that a handheld Raman spectrometer equipped with a 532-nm laser as well as a portable dual instrument with 532/785-nm excitation was used in mineralogy.…”

11th International GeoRaman Conference

“…They report that carotenoids residing in the bacterial membranes were less sensitive to photodegradation than the mineral matrix. Harris et al investigated several terrestrial Mars analogue samples to point out a cautionary tale to the astrobiology community potential for confusion in interpreting Raman spectra acquired from these types of samples. Foucher et al demonstrates the potential of Raman mapping of the distribution and change in intensity ratio of the D and G bands arising from carbonaceous material as a biosignature to help identify potential fossilized microbes here in early Earth rocks and Mars.…”