Cavity-enhanced laser spectroscopic studies of vibrational overtones of acetylene

This thesis contains five experimental spectroscopic studies that probe the vibration-rotation energy level structure of acetylene and some of its isotopologues. The emphasis is on the development of laser spectroscopic methods for high-resolution molecular spectroscopy. Three of the experiments use cavity ringdown spectroscopy. One is a standard setup that employs a non-frequency stabilised continuous wave laser as a source. In the other two experiments, the same laser is actively frequency stabilised to the ringdown cavity. This development allows for increased repetition rate of the experimental signal and thus the spectroscopic sensitivity of the method is improved. These setups are applied to the recording of several vibration-rotation overtone bands of both H(12)C(12)CH and H(13)C(13)CH. An intra-cavity laser absorption spectroscopy setup that uses a commercial continuous wave ring laser and a Fourier transform interferometer is presented. The configuration of the laser is found to be sub-optimal for high-sensitivity work but the spectroscopic results are good and show the viability of this type of approach. Several ro-vibrational bands of carbon-13 substituted acetylenes are recorded and analysed. Compared with earlier work, the signal-to-noise ratio of a laser-induced dispersed infrared fluorescence experiment is enhanced by more than one order of magnitude by exploiting the geometric characteristics of the setup. The higher sensitivity of the spectrometer leads to the observation of two new symmetric vibrational states of H(12)C(12)CH. The precision of the spectroscopic parameters of some previously published symmetric states is also improved. An interesting collisional energy transfer process is observed for the excited vibrational states and this phenomenon is explained by a simple step-down model.Väitöskirja käsittelee kokeellista korkean erotuskyvyn molekyylispektroskopiaa. Neljä erilaista lasereihin perustuvaa koejärjestelyä on rakennettu ja näitä kaikkia on sovellettu kaasumaisen asetyleenin (HCCH) ja sen eri hiili-13 isotooppivaihdettujen isotopomeerien värähtelyspektrien mittaamiseen. Värähtelyspektrit on mitattu lähi-infrapuna-alueella, missä säteilykentän energia riittää virittämään molekyyliä useamman värähtelykvantin verran. Spektrit koostuvat siirtymistä molekyylin pyörimiseen ja värähtelyyn liittyvien energiatilojen välillä. Tutkimuksessa on käytetty sekä absorptiospektroskopiaa että emissiospektroskopiaa. Emissiokoe on ainutlaatuinen, siinä tutkitaan asetyleenin fluoresenssia elektronisen perustilan sisällä, eri värähtelytilojen välillä. Absorptiokokeet perustuvat ontelovaimenemisspektroskopiaan ja laserontelon sisäiseen absorptiospektroskopiaan. Kaikki koejärjestelyt käyttävät hyväkseen peileistä muodostettujen optisten onteloiden ominaisuuksia. Joko koe on suoritettu laserontelon sisällä tai laserin säde on kytketty erilliseen ulkoiseen onteloon. Etuna on onteloiden sisälle saatava suuri optinen teho ja tietyissä tapauksissa niiden kautta saatava suuri absorptiomatka. Nämä tekijät auttavat parantamaan kokeiden herkkyyttä, eli kokeellisen signaalin voimakkuutta suhteessa kohinaan. Erilaisten uusien koejärjestelyjen lisäksi tutkimus on tuottanut uutta tietoa asetyleenin värähtelyyn ja pyörimiseen liittyvistä energiatiloista. Erityisesti ns. symmetrisiä värähtelytiloja on päästy tutkimaan ainutlaatuisen värähtelyfluoresenssilaitteiston avulla. Kaikki kokeissa mitatut spektrit on tulkittu käyttäen sopivia kvanttimekaanisia malleja, ja tuloksena on joukko malliin littyviä molekyyliparametrejä. Nämä mittaustulokset ovat potentiaalisesti hyödyllisiä sekä kemian perustutkimuksessa että myös soveltavassa tutkimuksessa mm. tähtitieteen alalla

Volatile composition of the morning breath

We have measured the composition of volatile organic compounds (VOCs) in the morning breath of 30 healthy individuals before and after tooth brushing. The concentrations of VOCs in the breath samples were measured with proton-transfer-reaction time-of-flight mass spectrometry (MS) and further identification was performed with a combination of solid phase microextraction and offline gas chromatography-MS. We hypothesize that compounds, whose concentrations significantly decreased in the breath after tooth brushing are largely of microbial origin. In this study, we found 35 such VOCs. Out of these, 33 have been previously connected to different oral niches, such as salivary and subgingival bacteria. We also compared the concentrations of the 35 VOCs found in increased amounts in the morning breath to their respective odor thresholds to evaluate their ability to cause odor. Compounds that could contribute to the breath odor include many volatile sulfur compounds, such as methanethiol, hydrogen sulfide, dimethyl sulfide, and 2-methyl-1-propanethiol, but also other VOCs, such as acetic acid, butyric acid, valeric acid, acetaldehyde, octanal, phenol, indole, ammonia, isoprene, and methyl methacrylate.Peer reviewe

Frequency comb assisted two-photon vibrational spectroscopy

We report a setup for high-resolution two-photon spectroscopy using a mid-infrared continuous wave optical parametric oscillator (CW-OPO) and a near-infrared diode laser as the excitation sources, both of which are locked to fully stabilized optical frequency combs. The diode laser is directly locked to a commercial near-infrared optical frequency comb using an optical phase-locked loop. The near-infrared frequency comb is also used to synchronously pump a degenerate femtosecond optical parametric oscillator to produce a fully stabilized mid-infrared frequency comb. The beat frequency between the mid-infrared comb and the CW-OPO is then stabilized through frequency locking. We used the setup to measure a double resonant two-photon transition to a symmetric vibrational state of acetylene with a sub-Doppler resolution and high signal-to-noise ratio. (C) 2017 Optical Society of AmericaPeer reviewe

Step-modulated decay cavity ring-down detection for double resonance spectroscopy

A method of measuring double resonant two-photon signal and background from a single cavity ring-down decay is introduced. This is achieved by modulating the double resonance loss via one of the light sources exciting the transition. The noise performance of the method is characterized theoretically and experimentally. The addition of a new parameter to the fitting function introduces a minor noise increase due to parameter correlation. However, the concurrent recording of the background can extend the stable measurement time. Alternatively, the method allows a faster measurement speed, while still recording the background, which is often advantageous in double resonance measurements. Finally, the method is insensitive to changes in the cavity decay rate at short timescales and can lead to improved performance if they have significant contribution to the final noise level compared to the detector noise. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing AgreementPeer reviewe

Experimental observation and analysis of the 3v(1)(Sigma g) stretching vibrational state of acetylene using continuous-wave infrared stimulated emission

Peer reviewe

Reduction of FENO by tap water and carbonated water mouthwashes : magnitude and time course

Fractional exhaled nitric oxide (F-ENO) assesses eosinophilic inflammation of the airways, but F-ENO values are also influenced by oral nitric oxide (NO). The aim of this pilot study was to measure F-ENO and compare the effect of two different mouthwashes on F-ENO and analyse the duration of the effect. F-ENO was measured in 12 randomized volunteers (healthy or asthmatic subjects) with a NIOX VERO (R) analyser at an expiratory flow rate of 50mL/s. After a baseline measurement, a mouthwash was performed either with tap water or carbonated water and was measured during 20min in 2min intervals. The procedure was repeated with the other mouthwash. We found that both mouthwashes reduced F-ENO immediately at the beginning compared to the baseline (pPeer reviewe

Antibiotic treatment and supplemental hemin availability affect the volatile organic compounds produced by P. gingivalis in vitro

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Electrostatic trapping of metastable NH molecules

We report on the Stark deceleration and electrostatic trapping of $^{14}$NH ($a ^1\Delta$) radicals. In the trap, the molecules are excited on the spin-forbidden $A ^3\Pi \leftarrow a ^1\Delta$ transition and detected via their subsequent fluorescence to the $X ^3\Sigma^-$ ground state. The 1/e trapping time is 1.4 $\pm$ 0.1 s, from which a lower limit of 2.7 s for the radiative lifetime of the $a ^1\Delta, v=0,J=2$ state is deduced. The spectral profile of the molecules in the trapping field is measured to probe their spatial distribution. Electrostatic trapping of metastable NH followed by optical pumping of the trapped molecules to the electronic ground state is an important step towards accumulation of these radicals in a magnetic trap.Comment: replaced with final version, added journal referenc

L-Cysteine Containing Vitamin Supplement Which Prevents or Alleviates Alcohol-related Hangover Symptoms : Nausea, Headache, Stress and Anxiety

Correction ALCOHOL AND ALCOHOLISM Volume: 55 Issue: 6 Pages: 705-705 DOI: 10.1093/alcalc/agaa088 Published: NOV 2020Aims: Alcohol-related hangover symptoms: nausea, headache, stress and anxiety cause globally considerable amount of health problems and economic losses. Many of these harmful effects are produced by alcohol and its metabolite, acetaldehyde, which also is a common ingredient in alcohol beverages. The aim of the present study is to investigate the effect of the amino acid L-cysteine on the alcohol/acetaldehyde related aftereffects. Methods: Voluntary healthy participants were recruited through advertisements. Volunteers had to have experience of hangover and/or headache. The hangover study was randomized, double-blind and placebo-controlled. Nineteen males randomly swallowed placebo and L-cysteine tablets. The alcohol dose was 1.5 g/kg, which was consumed during 3 h. Results: The primary results based on correlational analysis showed that L-cysteine prevents or alleviates hangover, nausea, headache, stress and anxiety. For hangover, nausea and headache the results were apparent with the L-cysteine dose of 1200 mg and for stress and anxiety already with the dose of 600 mg. Conclusions: L-cysteine would reduce the need of drinking the next day with no or less hangover symptoms: nausea, headache, stress and anxiety. Altogether, these effects of L-cysteine are unique and seem to have a future in preventing or alleviating these harmful symptoms as well as reducing the risk of alcohol addiction.Peer reviewe

Broadband photoacoustic spectroscopy of 14CH4 with a high-power mid-infrared optical frequency comb

We report a photoacoustic spectroscopy setup with a high-power mid-infrared frequency comb as the light source. The setup is used in broadband spectroscopy of radiocarbon methane. Owing to the high sensitivity of a cantilever-enhanced photoacoustic cell and the high-power light source, we can reach a detection limit below 100 ppb in a broadband measurement with a sample volume of only a few milliliters. The first infrared spectrum of 14CH4 is reported and given a preliminary assignment. The results lay a foundation for the development of optical detection systems for radiocarbon methane.We report a photoacoustic spectroscopy setup with a high-power mid-infrared frequency comb as the light source. The setup is used in broadband spectroscopy of radiocarbon methane. Owing to the high sensitivity of a cantilever-enhanced photoacoustic cell and the high-power light source, we can reach a detection limit below 100 ppb in a broadband measurement with a sample volume of only a few milliliters. The first infrared spectrum of (CH4)-C-14 is reported and given a preliminary assignment. The results lay a foundation for the development of optical detection systems for radiocarbon methane. (c) 2019 Optical Society of AmericaPeer reviewe