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Instruments – University of Copenhagen

The Kjaergaard Group > Instruments


Conventional Fourier Transform Infrared (FTIR) Spectroscopy

FTIR spectroscopy is a technique, which measures how much infrared radiation a sample absorbs at each wavelength. It consists of a light source, which hits an interferometer consisting of a beam splitter. Here the infrared radiation from the light source is divided into two beams resulting in an optical path difference between the beams. The beams hit a mirror and are recombined and directed towards the sample. Behind the sample a detector records the repetitive interference signals from the collected beams, which is subsequently decoded into an absorption spectrum by Fourier transformation. 

We use this technique to study the fundamental vibration and lower vibrational overtones of mononuclear species as well as hydrogen-bonded complexes.

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Matrix Isolation Spectroscopy

In Matrix Isolation Spectroscopy a sample is trapped in a large medium of inert gas such as Ar, which is then cooled down. This results in the sample being trapped in the rigid matrix of Ar. The sample can then be examined spectroscopically whilst trapped in the matrix. This technique is therefore useful when examining reactive or unstable species such as hydrogen bonded complexes or radicals as the matrix stabilizes the species by separating them.

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Ultraviolet-Visible (UV-Vis) Spectroscopy

UV-Vis spectroscopy is a technique, which measures how much ultraviolet and visible radiation a sample absorbs at each wavelength. A light source is directed into a monochromater, which only allows a very narrow range of wavelengths to go through it. After going through the monochromater the light passes through a sample and is detected on the other side. The intensity of the light passing through a sample is compared to the intensity of the light before it passes through the sample and an absorbance spectrum is recorded.

We use this technique to study the electronic transitions in different species as well as XH-stretching vibrational overtones.

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Time Resolved Step-scan FTIR

In time resolved step-scan FTIR a reaction or excitation is initiated with light and an FTIR spectrum at different times following the initiation is monitored. In order to follow a reaction or excitation as it evolves in time, the measurement process must be faster than the reaction times. It is possible to monitor the intensity of a single frequency over time, which makes it possible to follow the change in concentration of a given molecule as a function of time. The changes to the FTIR spectrum as a function of time can thereby reveal the identity of reaction products, intermediates and reactants and time resolved step-scan FTIR is therefore a useful tool in the investigation of the kinetics and mechanisms of a reaction. This technique is also used to examine long-lived triplet excited states.

Intracavity Laser Photoacoustic Spectroscopy (ICL-PAS)

Photoacoustic spectroscopy is a technique, in which a pulsed laser or modulated laser is directed towards a gaseous sample. When light is absorbed by the gas sample, the excited molecules will subsequently relax to the ground state either by emission of photons or by means of non-radiative processes. The non-radiative processes produce localized heating in the sample, resulting in an increase in the local pressure of the sample. By using a pulsed/modulated laser, the sample pressure will also modulate creating a sound wave. This sound wave will have the same frequency as the initial light modulation, making it possible to use a microphone to generate an absorbance spectrum of the gas sample. The photoacoustic signal can be amplified by tuning the modulation/pulse of the laser, so it will resonate with the gas sample.

We apply this technique, when we want to explore high vibrational XH-stretching overtones.

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Cavity Ring-down Spectroscopy

We have very recently installed a cavity ring-down spectrometer in our lab. Cavity ring-down spectroscopy (CRDS) is a very sensitive technique. A short laser pulse is directed into a cavity between two highly reflective mirrors. Every time the laser pulse reaches a mirror a small fraction of the light leaks out through the mirror. In an empty cavity the decay rate of the laser light between the mirrors is dependent only on the reflectivity of the mirrors but when absorbing sample is present, the decay happens faster. The decay of the light intensity measured on the other side of the mirror is converted to absorbance. A factor that significantly adds to the sensitivity of this technique is the effective optical path length, which reaches up to orders of several kilometres with a cavity length below a meter. This also means that the sample volume does not have to be large in order to record a spectrum of it using CRDS.

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Raman Spectroscopy

Monochromatic light is directed at a sample where it interacts with vibrations and other excitations in the system, which changes the wavelength of the incident light. On the other side of the sample a detector measures the wavelength and intensity of the radiation. Elastically scattered light with the same wavelength as the incident light is filtered out.

We have used Raman spectroscopy in the CN-stretching frequencies to characterize dihydroazulene and vinylheptafulvene derivatives. 

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High Performance CPU Cluster

The high performance CPU cluster enables us to run high level quantum mechanical calculations in Gaussian 09 and MolPro 2012 amongst others. We have access to 4700 CPUs with a total of 24 TB RAM.

We have used our high performance CPU cluster to calculate reaction rates in atmospheric radical reactions as well as calculate vibrational transitions, energies and geometric values of molecules of spectroscopic interest.

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