Trace gas detection and high-precision spectroscopy in the mid-infrared and visible wavelength regions

This thesis is based on four experimental spectroscopic studies where novel highly sensitive laser absorption spectroscopy spectrometers are developed and used for trace gas detection and precision spectroscopy. Most of the studies are carried out in the mid-infrared region between 3 and 4 µm, where a homebuilt continuous-wave singly resonating optical parametric oscillator is used as a light source. In addition, one study has been performed in the visible region using a commercial green laser at 532 nm. Two of the developed spectroscopic applications are based on cavity ring-down spectroscopy. In this thesis, the first off-axis re-entrant cavity ring-down spectrometer in the mid-infrared is demonstrated and utilized for highly sensitive detection of formaldehyde. The second study presents an optical frequency comb referenced mid-infrared continuous-wave singly resonating optical parametric oscillator, which is applied to high-precision cavity ring-down spectroscopy of nitrous oxide and methane. Furthermore, this study presents a new method for referencing a mid-infrared optical parametric oscillator to a near-infrared optical frequency comb. This new method allows large mode-hop-free frequency tuning ranges in the mid-infrared region. The other two experiments are based on cantilever-enhanced photoacoustic spectroscopy, presenting the first reported studies of cantilever-enhanced-based trace gas detection in the mid-infrared and visible region. These studies show the great potential of cantilever-enhanced photoacoustic detection for substantial enhancement of the sensitivity of trace gas detection. For instance, the best nitrogen dioxide detection limit ever reported using photoacoustic spectroscopy is presented in this thesis.Tämä väitöskirja sisältää neljä laserspektroskopiaan perustuvaa kokeellista tutkimusta. Tutkimuksissa on kehitetty uusia, korkeaan spektroskooppiseen erotuskykyyn ja suureen herkkyyteen perustuvia mittausmenetelmiä ja mittalaitteita ympäristön kannalta tärkeiden, pienimolekyylisten kaasutilassa esiintyvien yhdisteiden (hivenkaasujen) havaitsemiseksi. Tällaisia hivenkaasuja ovat mm. dityppioksidi (N2O), formaldehydi (CH2O), metaani (CH4), typpidioksidi (NO2) ja vetysyanidi (HCN), joista esimerkiksi CH4 ja N2O ovat ilmastonmuutoksen ja CH2O sisäilman laadun kannalta tärkeitä yhdisteitä. Lisäksi autojen polttomoottorit ja voimalaitokset tuottavat ilmakehään mm. haitallisia typen oksideita, kuten NO2:ta. Kyseisten hivenkaasujen suhteelliset pitoisuudet näytematriisissa (esim. ilmakehässä) ovat tyypillisesti erittäin pieniä (miljoonas-, miljardis- tai jopa biljoonasosia), joten niiden havaitsemiseen tarvitaan erittäin herkkiä mittausmenetelmiä. Laserspektroskopialla on mahdollista havaita (''haistaa'') näitä yhdisteitä herkästi ja usein myös reaaliaikaisesti. Etenkin keski-infrapuna-alueella eli niin kutsutulla sormenjälkialueella, jossa sijaitsee esimerkiksi useimpien hiilivetyjen voimakkaimmat absorptiot. Väitöskirjassa kehitetyt spektrometrit on toteutettu yhtä lukuun ottamatta keski-infrapuna-alueella ja ne perustuvat ontelovaimenemisspektroskopiaan sekä valoakustiseen spektroskopiaan. Tässä väitöskirjassa kehitettiin keski-infrapuna-alueen ei-aksiaalinen ontelovaimenemisspektrometri formaldehydille, joka mahdollistaa alle sadan miljardisosan suhteellisten formaldehydipitoisuuksien nopean mittaamisen. Tässä väitöskirjassa kehitettiin myös yhteistyössä mittatekniikankeskuksen (MIKES-VTT Oy) kanssa uudenlainen ontelovaimenemisspektrometri, jolla on mahdollista määrittää molekyylien, kuten dityppioksidin ja metaanin absorptiovoimakkuuksia ja niiden keskitaajuuksia absoluuttisen tarkasti (jäljitettävästi) sormenjälkialueella. Näitä perustutkimuksenkin kannalta tärkeitä spektroskooppisia määreitä voidaan hyödyntää mm. ilmastonmuutoksen mallinnuksessa. Lisäksi tässä väitöskirjassa kehitettiin yhteistyössä Gasera Oy:n kanssa valoakustiseen spektroskopiaan perustuva mittalaite HCN:lle ja CH4:lle, sekä mittalaite ympäristölle haitalliselle, erityisesti dieselmoottoreissa syntyvälle typpidioksidille. Tässä väitöskirjassa saavutettu 50:n biljoonasosan suhteellinen havaintoraja NO2:lle on pienin koskaan raportoitu tulos käyttäen valoakustista spektroskopiaa. Kyseinen NO2-tutkimus toteutettiin muista tutkimuksista poiketen näkyvän valon alueella. Tässä väitöskirjatyössä kehitettyjen laserspektroskopiaan perustuvien menetelmien ja mittalaitteiden erinomainen herkkyys perustuu ulkoisten optisten onteloiden tarjoamaan pitkään absorptiomatkaan sekä valoakustisen signaalin uudenlaiseen mittaamiseen erittäin herkällä piiliuskalla (''optinen mikrofoni''), ja erityisesti näiden kahden menetelmän yhdistämiseen ensimmäistä kertaa keski-infrapuna-alueen ja näkyvän valon alueen lasereiden kanssa. Kyseiset menetelmät eivät sovellu ainoastaan yllä mainituille yhdisteille, vaan niitä on mahdollista soveltaa myös muiden ilmakehässä esiintyvien sekä ihmisen että luonnon emittoimien pienimolekyylisten kaasujen havainnointiin etenkin keski-infrapuna-alueella

Time-resolved, broadband UV-absorption spectrometry measurements of Criegee intermediate kinetics using a new photolytic precursor : unimolecular decomposition of CH2OO and its reaction with formic acid

We present a time-resolved broadband cavity-enhanced UV-absorption spectrometer apparatus that we have constructed and utilized for temperature- and pressure-dependent kinetic measurements of formaldehyde oxide (CH2OO) reactions. We also introduce and utilize a new photolytic precursor, bromoiodomethane (CH2IBr), which photolysis at 213 nm in presence of O2 produces CH2OO. Importantly, this precursor appears to be free from secondary reactions that may regenerate CH2OO in kinetic experiments. The unimolecular decomposition rate coefficient of CH2OO has been measured over wide pressure (5–400 Torr) and temperature (296–600 K) ranges and master equation simulations of the decomposition kinetics have been performed using MESMER program. The MESMER simulations of the experimental data with the calculated zero-point energy corrected transition state energy 85.9 kJ mol−1 for decomposition required no adjustment and returned 〈ΔE〉down = 123.2 × (T/298 K)0.74 cm−1 for temperature-dependent exponential-down model of the collisional energy transfer in He. A very good agreement between results of simulations and experiments is obtained. The results are compared with the previously reported unimolecular decomposition study by Stone et al. (Phys. Chem. Chem. Phys., 2018, 20, 24940–24954). Current master equation simulations suggest about 61% decomposition yield for the predominant H2 + CO2 channel, whereas the yields of two other channels, H2O + CO, and HCO + OH, are sensitive on the parameters involved in the simulations. The kinetics of CH2OO reaction with formic acid has also been investigated as function of pressure (5–150 Torr) and temperature (296–458 K). The bimolecular rate coefficient for CH2OO + HCOOH reaction shows a negative temperature dependency, decreasing from (1.0 ± 0.03) × 10−10 cm3 molecule−1 s−1 at 296 K to (0.47 ± 0.05) × 10−10 cm3 molecule−1 s−1 at 458 K with an Arrhenius activation energy of −4.9 ± 1.6 kJ mol−1, where statistical uncertainties shown are 2σ. Estimated overall uncertainty in the measured rate coefficients is about ±20%. Current bimolecular rate coefficient at room temperature agrees with the previously reported rate coefficients from the direct kinetic experiments. The reaction is found to be pressure independent over the range between 5 and 150 Torr at 296 K in He.We present a time-resolved broadband cavity-enhanced UV-absorption spectrometer apparatus that we have constructed and utilized for temperature- and pressure-dependent kinetic measurements of formaldehyde oxide (CH2OO) reactions. We also introduce and utilize a new photolytic precursor, bromoiodomethane (CH2IBr), which photolysis at 213 nm in presence of O-2 produces CH2OO. Importantly, this precursor appears to be free from secondary reactions that may regenerate CH2OO in kinetic experiments. The unimolecular decomposition rate coefficient of CH2OO has been measured over wide pressure (5-400 Torr) and temperature (296-600 K) ranges and master equation simulations of the decomposition kinetics have been performed using MESMER program. The MESMER simulations of the experimental data with the calculated zero-point energy corrected transition state energy 85.9 kJ mol(-1) for decomposition required no adjustment and returned (down) = 123.2 x (T/298 K)(0.74) cm(-1) for temperature-dependent exponential-down model of the collisional energy transfer in He. A very good agreement between results of simulations and experiments is obtained. The results are compared with the previously reported unimolecular decomposition study by Stone et al. (Phys. Chem. Chem. Phys., 2018, 20, 24940-24954). Current master equation simulations suggest about 61% decomposition yield for the predominant H-2 + CO2 channel, whereas the yields of two other channels, H2O + CO, and HCO + OH, are sensitive on the parameters involved in the simulations. The kinetics of CH2OO reaction with formic acid has also been investigated as function of pressure (5-150 Torr) and temperature (296-458 K). The bimolecular rate coefficient for CH2OO + HCOOH reaction shows a negative temperature dependency, decreasing from (1.0 +/- 0.03) x 10(-10) cm(3) molecule(-1) s(-1) at 296 K to (0.47 +/- 0.05) x 10(-10) cm(3) molecule(-1) s(-1) at 458 K with an Arrhenius activation energy of -4.9 +/- 1.6 kJ mol(-1), where statistical uncertainties shown are 2 sigma. Estimated overall uncertainty in the measured rate coefficients is about +/- 20%. Current bimolecular rate coefficient at room temperature agrees with the previously reported rate coefficients from the direct kinetic experiments. The reaction is found to be pressure independent over the range between 5 and 150 Torr at 296 K in He.Peer reviewe

Solving the discrepancy between the direct and relative-rate determinations of unimolecular reaction kinetics of dimethyl- substituted Criegee intermediate (CH3)2COO using a new photolytic precursor

We have performed direct kinetic measurements of thermal unimolecular reaction of (CH3)2COO in the temperature 243– 340 K and pressure 5–350 Torr ranges using time-resolved UV-absorption spectroscopy. We have utilized a new photolytic precursor, 2-bromo-2-iodopropane ((CH3)2CIBr), which photolysis at 213 nm in presence of O2 produces acetone oxide, (CH3)2COO. The results show that the thermal unimolecular reaction is more important main loss process of (CH3)2COO in the atmosphere than direct kinetic studies hitherto suggest. The current experiments show that the unimolecular reaction rate of (CH3)2COO at 296 K and atmospheric pressure is 899 ± 42 s-1. Probably more importantly, current measurements bring the direct and relative rate measurements of thermal unimolecular reaction kinetics of (CH3)2COO in quantitative agreement.Peer reviewe

Maatalouden ympäristöohjelma 1995-1999:n taloudellinen analyysi : ympäristötukijärjestelmä ja tulevaisuus -tutkimuksen loppuraportti

vokMTT Taloustutkimu

An Experimental and Master Equation Investigation of Kinetics of the CH2OO+RCN Reactions (R = H, CH3, C2H5) and Their Atmospheric Relevance

We have performed direct kinetic measurements of the CH2OO + RCN reactions (R = H, CH3, C2H5) in the temperature range 233-360 K and pressure range 10-250 Torr using time-resolved UV-absorption spectroscopy. We have utilized a new photolytic precursor, chloroiodomethane (CH2ICl), whose photolysis at 193 nm in the presence of O2 produces CH2OO. Observed bimolecular rate coefficients for CH2OO + HCN, CH2OO + CH3CN, and CH2OO + C2H5CN reactions at 296 K are (2.22 +/- 0.65) x 10-14 cm3 molecule-1 s-1, (1.02 +/- 0.10) x 10-14 cm3 molecule-1 s-1, and (2.55 +/- 0.13) x 10-14 cm3 molecule-1 s-1, respectively, suggesting that reaction with CH2OO is a potential atmospheric degradation pathway for nitriles. All the reactions have negligible temperature and pressure dependence in the studied regions. Quantum chemical calculations (omega B97X-D/aug-cc-pVTZ optimization with CCSD(T)-F12a/VDZ-F12 electronic energy correction) of the CH2OO + RCN reactions indicate that the barrierless lowest-energy reaction path leads to a ring closure, resulting in the formation of a 1,2,4-dioxazole compound. Master equation modeling results suggest that following the ring closure, chemical activation in the case of CH2OO + HCN and CH2OO + CH3CN reactions leads to a rapid decomposition of 1,2,4-dioxazole into a CH2O + RNCO pair, or by a rearrangement, into a formyl amide (RC(O)NHC(O)H), followed by decomposition into CO and an imidic acid (RC(NH)OH). The 1,2,4-dioxazole, the CH2O + RNCO pair, and the CO + RC(NH)OH pair are atmospherically significant end products to varying degrees.Peer reviewe

Being watched by a humanoid robot and a human: Effects on affect-related psychophysiological responses

publishedVersionPeer reviewe

Frequency-comb-referenced mid-infrared source for high-precision spectroscopy

We report on a tunable continuous-wave mid-infrared optical parametric oscillator (OPO), which is locked to a fully stabilized near-infrared optical frequency comb using a frequency doubling scheme. The OPO is used for 40 GHz mode-hop-free, frequency-comb-locked scans in the wavelength region between 2.7 and 3.4 x03BC;m. We demonstrate the applicability of the method to high-precision cavity-ring-down spectroscopy of nitrous oxide (N2O) and water (H2O) at 2.85 x00B5;m and of methane (CH4) at 3.2 x03BC;m.Peer reviewe

Psychophysiological responses to eye contact with a humanoid robot: Impact of perceived intentionality

Eye contact with a social robot has been shown to elicit similar psychophysiological responses to eye contact with another human. However, it is becoming increasingly clear that the attention- and affect-related psychophysiological responses differentiate between direct (toward the observer) and averted gaze mainly when viewing embodied faces that are capable of social interaction, whereas pictorial or pre-recorded stimuli have no such capability. It has been suggested that genuine eye contact, as indicated by the differential psychophysiological responses to direct and averted gaze, requires a feeling of being watched by another mind. Therefore, we measured event-related potentials (N170 and frontal P300) with EEG, facial electromyography, skin conductance, and heart rate deceleration responses to seeing a humanoid robot's direct versus averted gaze, while manipulating the impression of the robot's intentionality. The results showed that the N170 and the facial zygomatic responses were greater to direct than to averted gaze of the robot, and independent of the robot's intentionality, whereas the frontal P300 responses were more positive to direct than to averted gaze only when the robot appeared intentional. The study provides further evidence that the gaze behavior of a social robot elicits attentional and affective responses and adds that the robot's seemingly autonomous social behavior plays an important role in eliciting higher-level socio-cognitive processing.Peer reviewe