Photoacoustic spectroscopy of 14CH4 using a mid-infrared optical parametric oscillator

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dc.contributor Helsingin yliopisto, Matemaattis-luonnontieteellinen tiedekunta fi
dc.contributor University of Helsinki, Faculty of Science en
dc.contributor Helsingfors universitet, Matematisk-naturvetenskapliga fakulteten sv
dc.contributor.author Larnimaa, Santeri
dc.date.issued 2020
dc.identifier.uri URN:NBN:fi:hulib-202006233413
dc.identifier.uri http://hdl.handle.net/10138/316932
dc.description.abstract Radiomethane (14CH4) is a radioactive isotopologue of methane known to be emitted from nuclear facilities. As methane is a potent greenhouse gas and measuring the concentration of carbon-14 in a methane sample gives information about the origin of the sample, it is important to be able monitor 14CH4. The state-of-the-art method for radiomethane measurements is accelerator mass spectrometry, but optical methods have also been proposed due their affordability and suitability for field measurements. Radiomethane has already been measured with optical methods, but usually indirectly by first combusting it to carbon dioxide – direct measurement of radiomethane with optical methods would require spectroscopic information, and the first absorption spectrum of radiomethane was measured only in the year 2019. In this thesis, the exploration of the CH-stretching vibrational band ν3 of 14CH4 is continued: Total of 43 lines with 17 new lines have been measured and assigned with improved accuracy. Furthermore, the widths of the lines have been studied in detail for the first time and a simple model to estimate the 14CH4 line positions to aid possible future research on radiomethane is presented. The measurements were conducted with photoacoustic spectroscopy using frequency modulation techniques and a mid-infrared continuous-wave optical parametric oscillator (OPO) as a light source. The OPO frequency was referenced to a wavelength meter and the frequency scanning (measuring over an absorption line) was executed with a proportional–integral–derivative controller in LabVIEW. The novel results presented in this thesis are useful for possible future applications in quantitative analysis of radiomethane, and the results are also relevant for fundamental research as radiomethane is the last naturally occurring isotopologue of methane that has not yet been extensively studied with optical methods. en
dc.language.iso eng
dc.publisher Helsingin yliopisto fi
dc.publisher University of Helsinki en
dc.publisher Helsingfors universitet sv
dc.subject Radiomethane
dc.subject methane
dc.subject carbon-14
dc.subject mid-infrared
dc.subject vibrational band
dc.subject optical methods
dc.subject photoacoustic spectroscopy
dc.subject frequency modulation
dc.subject optical parametric oscillator
dc.subject OPO
dc.subject linewidth
dc.title Photoacoustic spectroscopy of 14CH4 using a mid-infrared optical parametric oscillator en
dc.type.ontasot pro gradu -tutkielmat fi
dc.type.ontasot master's thesis en
dc.type.ontasot pro gradu-avhandlingar sv
dc.subject.discipline none und
dct.identifier.urn URN:NBN:fi:hulib-202006233413
dc.subject.specialization ei opintosuuntaa fi
dc.subject.specialization no specialization en
dc.subject.specialization ingen studieinriktning sv
dc.subject.degreeprogram Kemian ja molekyylitieteiden maisteriohjelma fi
dc.subject.degreeprogram Master's Programme in Chemistry and Molecular Sciences en
dc.subject.degreeprogram Magisterprogrammet i kemi och molekylära vetenskaper sv

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