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Assessing the electric-field approximation to IR and Raman spectra of dilute HOD in D2O
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
Stanford Synchrotron Radiation Lightsource.
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
2009 (engelsk)Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 131, s. 034501-Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

We analyze the validity of the commonly used electric-field (E-field) approximation to vibrational OH stretch Raman spectra of dilute HOD in D2O by computing the OH stretch frequency of all molecules in several different structure models, each containing around 2000 molecules. The calculations are done at the B3LYP level using clusters containing 32 molecules centered around the molecule for which the frequencies are calculated; the large cluster size is required due to significant nonlocal contributions influencing the computed frequencies. The vibrational frequencies are determined using a six-point potential optimized discrete variable representation. Raman and infrared intensities are furthermore computed to generate the spectra. We find that a quadratic fit of E-field versus frequency gives a reasonable representation of the calculated distribution of frequencies. However, the mapping depends significantly on the structural model and is thus not universal. Anharmonic couplings are calculated for several optimized clusters showing a general trend to compress the computed frequency distributions, which is in agreement with dynamical simulations (motional narrowing).

sted, utgiver, år, opplag, sider
2009. Vol. 131, s. 034501-
Identifikatorer
URN: urn:nbn:se:su:diva-31948DOI: 10.1063/1.3154144ISI: 000268206800035OAI: oai:DiVA.org:su-31948DiVA, id: diva2:279031
Tilgjengelig fra: 2009-12-01 Laget: 2009-12-01 Sist oppdatert: 2017-12-12bibliografisk kontrollert
Inngår i avhandling
1. Theoretical modeling of x-ray and vibrational spectroscopies applied to liquid water and surface adsorbates
Åpne denne publikasjonen i ny fane eller vindu >>Theoretical modeling of x-ray and vibrational spectroscopies applied to liquid water and surface adsorbates
2010 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

This thesis presents results of theoretical modeling of x-ray and vibrational spectroscopies applied to liquid water and to CO adsorbed on a Ni(100) surface. The Reverse Monte Carlo method is used to search for  water structures that reproduce diffraction, IR/Raman and x-ray absorption by fitting them to experimental data and imposed constraints. Some of the structures are created to have a large fraction of broken hydrogen bonds because recent x-ray absorption and emission studies have been seen to support the existence of such structures. In the fitting procedure a fast way of computing the IR/Raman spectrum for an isolated OH stretch is used, where the frequency is represented by the electric field projected in the direction of the stretch coordinate. This method is critically evaluated by comparing it to quantum chemical cluster calculations. Furthermore, the x-ray emission spectrum of water is investigated, the modeling of which is complicated by the necessity of including vibrational effects in the spectrum calculations due to a dissociative intermediate state. Based on the Kramers-Heisenberg formula a new semi-classical method is developed to include vibrational effects in x-ray emission calculations. The method is seen to work very well for a one-dimensional test system. Moreover, x-ray absorption and emission are implemented in a periodic Density Functional Theory code which is applied to ice and to the surface adsorbate system CO on Ni(100).

Abstract [sv]

Den här avhandlingen presenterar resultat av teoretisk modellering av röntgen- och vibrationella spektroskopier applicerade på flytande vatten och på CO adsorberat på en Ni(100) -yta. Reverse Monte Carlo-metoden används till att söka efter vattenstrukturer som reproducerar diffraktion, IR/Raman, röntgenabsorption och emission genom att anpassa strukturerna till experimentella data samt till pålagda restriktionsvillkor. Vissa av strukturerna är skapade så att de har en stor andel brutna vätebindningar eftersom nya röntgenabsorptions- och emissionsexperiment har setts stödja förekomsten av sådana strukturer. I anpassningsprocessen används en metod för att snabbt beräkna IR/Raman-spektrum för en isolerad OH-stretch, där frekvensen representeras av det elektriska fältet projicerat i stretch-koordinatens riktning.Vi utvärderar kritiskt denna metod genom att jämföra den med kvantkemiska klusterberäkningar. Vidare undersöks vattens röntgenemissionsspektrum, vars modellering kompliceras av nödvändigheten att inkludera vibrationella effekter i spektrumberäkningarna på grund av ett dissociativt intermediärt tillstånd. Baserat på Kramers-Heisenbergformeln utvecklas en ny semiklassisk metod som inkluderar vibrationella effekter. Metoden visar sig fungera mycket väl för ett endimensionellt testsystem. Dessutom implementerar vi röntgenabsorption och emission i en periodisk Täthetsfunktionalteorikod som vi sedan applicerar  på is och på ett ytadsorbatsystem: CO på Ni(100).

sted, utgiver, år, opplag, sider
Stockholm: Department of Physics, Stockholm University, 2010. s. 61
Emneord
water, XAS, XES, IR, Raman
HSV kategori
Forskningsprogram
kemisk fysik
Identifikatorer
urn:nbn:se:su:diva-38868 (URN)978-91-7447-096-3 (ISBN)
Disputas
2010-06-04, sal FR4, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (engelsk)
Opponent
Veileder
Merknad
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Manuscript. Paper 5: Manuscript. Paper 6: Manuscript.Tilgjengelig fra: 2010-05-11 Laget: 2010-05-03 Sist oppdatert: 2011-11-14bibliografisk kontrollert

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