An investigation into the relaxation of highly vibrationally excited trifluorobenzene and tetrafluorobenzene following collisions with carbon dioxide was performed using diode laser transient absorption spectroscopy. A 248 nm excimer laser prepared the vibrationally hot (E'~41,000 cm-1) fluorobenzene molecules. Large amounts of translational and rotational energy are transferred through collisions between the hot donor molecule and CO2. Rate constants and collisional probabilities were calculated by probing the high J states (J=58~80) of CO2 in the vibrational ground state, 0000, with measurements taken 1 µsec, ¼ the mean gas collision time, following each excimer laser pulse. The energy transfer probability distribution function, P(E,E'), was calculated for each molecule using the state-resolved probabilities and the energy gain of the bath. The study found a relationship between the fraction of strong collisions and the donor's dipole moment. Additionally, these findings support an application of Fermi's Golden rule to collisional energy transfer by linking the shape of P(E,E') to the shape of the donor's density of states as a function of ΔE.

This research is focused on single-collision energy transfer events between highly vibrationally excited benzene-like donor molecules and small bath molecules, CO2 and N2O in the vibrational ground level. Measuring how much energy is transferred from donors to bath molecules was accomplished by probing bath molecules scattered into specific-rotational states using a tunable Δv=0.0003 cm-1 solid state diode laser. The normalized energy transfer probability distribution function, P(E,E'), determined from energy gain information, is very useful in comparing collisional energy transfer efficiency between various collision systems. P(E,E') is also used to investigate the effects of donor and bath physical properties on collisional energy transfer. The first chapter details the C6H5F–CO2 system, which is the basis of a study on the effect of donor fluorination on strong collision energy transfer. The second chapter is about all fluorobenzene–CO2 systems, which investigates the effect of excess vibrational excitation energy of donors on supercollision energy transfer efficiency as well as donor fluorination effect. The third chapter focuses on how the physical properties of bath molecules affect supercollision energy transfer by measuring state-specific energy gain of N2O scattered into 0000, J=59−75. Instead of CO2, N2O was used as a bath molecule with a pyrazine donor to compare energy gain results of bath molecules with somewhat different physical properties. N2O and CO2 are isoelectronic and have similar mass, but N2O has a small dipole moment. Comparison of P(E,E') obtained from pyrazine–CO2, –N2O, –DCl, and –H2O systems helps to elucidate the effect of the bath physical properties on supercollision energy transfer efficiency. The last chapter is dedicated to the extension of the measurement range of N2O energy gain to the mid J states (J=37–75). In this chapter I discuss reliability of P(E,E') obtained from only high J tail as well as the correction of overall energy transfer rate constant.

Detta examensarbete presenterar resultatet från en experimentell studie med syfte att undersöka sambandet mellan ventilation i kontor och smittspridning av luftburna virus och bakterier. Fokuset i studien har framför allt riktats mot coronaviruset och även avgränsats till att enbart studera omblandande-, och deplacerande ventilation under den experimentella delen. Studien genomfördes i ett testrum lokaliserat vid Högskolan i Gävle. Syftet för studien har varit att besvara hur exponeringen av luftburna smittämnen förändras i andningszonen när distributionen av tilluften ändras och om placering av smittkällan i sig har någon betydelse. Studien har även haft för avsikt att besvara vilken utav deplacerande eller omblandande ventilation som lämpar sig bäst vad gäller minimering av överföringssannolikheten från en smittad persons andning. För att besvara studiens frågeställningar genomfördes spårgasmätningar och parallellt med spårgasmätningarna granskades även lufthastigheter och temperaturer på flera positioner i rummet. För omblandande ventilation undersöktes två olika riktningar på tilluftsstrålen, som valdes till vertikal och horisontell. För deplacerande ventilation undersöktes två olika inblåsningstemperaturer vilka var 21,3 ˚C och 16 ˚C. Resultatet av studiens experimentella del visade att deplacerande ventilation hade en mindre överföringssannolikhet vid jämförelse med omblandande ventilation. Detta då överföringssanolikheten låg på 0,3–0,5 % för omblandande och 0,1–0,3 % för deplacerande, vilket visar att deplacerande ventilation generellt varit på en lägre nivå oavsett position av smittkällan. Att deplacerande ventilation har en mindre benägenhet att sprida infektioner vidare bland olika individer i samma rum bekräftas också av flera tidigare artiklar som studerat ämnet. Då omblandande ventilation undersöktes visade studiens experimentella del att resultatet vad gäller riktningen på tilluftstrålen hade en inverkan på överföringssannolikheten. Den vertikala tilluftstrålen påverkade forceringen mellan de termiska dockor som placerades framför varandra, vilket resulterade i en minskning på överföringssannolikheten mitt emot de två olika positionerna där de infekterade dockorna satt. För bägge ventilationssystemen - förutom vid vertikal riktning på tilluftstrålen vid omblandande ventilation - visade avståndet mellan smittkällan och frånluftsdonet ha en effekt på smittspridningen. Detta eftersom överföringssanolikheten varit lägre vid placeringen mitt emot smittkällan och diagonalt från smittkällan vilket är ett större avstånd än vad positionering bredvid smittkällan är. Vad gäller deplacerande ventilation har placeringen av smittkällan visat effekt då överföringssannolikheten varit lägre vid placering av smittkällan närmare frånluftdonet samt att det minsta avståndet från smittkällan i det fallet haft lägst överföringssannolikhet. / This thesis presents the results of an experimental study with the aim to investigate the connection between ventilation in offices and spread of airborne viruses and bacteria. The focus is on coronavirus and this thesis only investigates mixed ventilation and displacement ventilation in the experimental part. The study is done in a full scale mook up room located in Högskolan i Gävle. The aim of the study was to answer how the exposure of airborne diseases change in the breathing zone when the distribution of supply air changes and if placement of the source of infection has any affect. The study also aims to investigate if displacement or mixing ventilation is the best choice to minimize transfer probability from an infected persons breath. Tracer gas measurements was done to answer the main questions. The tracer gas measurements were studied parallel to measurements of air velocities and temperatures on several positions in the room. For mixing ventilation, the measurements were done for two different directions of supply air jet, vertical and horizontal. For displacement ventilation measurements are done for two different temperatures on the supply air which was 21,3 ˚C and 16 ˚C. The results of the experimental part of this study showed that displacement ventilation had a lower transfer probability between an infected person and a non-infected person when compared to mixing ventilation. The transfer probability was 0,3 – 0,5 % for mixing ventilation and 0,1 – 0,3 % for displacement ventilation, which shows that displacement ventilation is generally at a lower level than mixing ventilation regardless of the position of the source of infection. The result in this thesis is like results found in the literature review which also shows that displacement ventilation has a lower tendency to spread infections between persons in the same room. The result for mixing ventilation regarding the direction of the supply air jet showed an impact on the transfer probability. The vertical supply air jet was affecting the force of the breath jet between the thermal manikin placed in front of each other, which is done as part of reduction in the transfer probability at the two different positions for the same direction of the supply air jet. For both ventilation systems – except for the vertical direction of the supply air jet in the case of mixing ventilation - the distance between the source of infection and exhaust diffuser has been shown to have an impact on the transfer probability. This means the transfer probability was lower at the location opposite the source of infection and diagonally from the source of infection, which is a greater distance than the location next to the source of infection. In terms of displacement ventilation, the location of the source of infection has shown an effect as the transfer probability was lower when the source of infection was placed closer to the exhaust diffuser and that the minimum distance from the source of infection in that case was the lowest.