PC-Praktikum

Spontaneous emission of radiation from an electrically excited species (contains both fluorescence and phosphorescence)

Emission of radiation from an electrically excited species (within ps-ns) without a change in multiplicity (small red-shift)

Spontaneous emission of radiation from an electrically excited species with a change in multiplicity (large red-shift).

Long excited state lifetime.

The electron prefers the transition to the excited state with the biggest overlap integral of the two wavefunctions. This occurs as a vertical transition, which means, that the nuclear geometry remains the same.

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\(\tau = {1 \over k_{radiation}}\)

\(\tau = {1 \over k_{radiation}+k_{non radiative}}\)

\(\Phi = {N_{emitted photons}\over N{absorbed photons}}\)

A process where another species present in the sample leads to a non-radiative relaxation from the excited state.

The halides are more efficient at quenching if they are large.

Die Stern-Volmer-Gleichung beschreibt in der Physikalischen Chemie die Abhängigkeit der Quantenausbeute bzw. der Intensität der Fluoreszenz eines fluoreszierenden Farbstoffes von der Konzentration von Stoffen, die die Fluoreszenz löschen (sogenannte Quencher)

\({F_0 \over F_{quench}} = 1+{K}*[Q]\)

Fo, Fluoreszenzintensität ohne Quencher

K: Stern-Vollmer-Konstante

[Q]: Konz. des Quenchers

Präzession d. Drehimpulses eines Teilchens mit einem magnetischen Dipolmoment um die Richtung eines von aussen angelegten Magnetfeldes.

\(\mu = \gamma * p, \gamma: gyromagnetisches Verhältnis\), p: Kernspin

At equilibrium the net magnetiziaton lies along the applied magnetic field and is called the equilibrium magnetization.  The return of the spin states to equil. and the spin exchange energy with its surroundings.

T1 is determined by an exponential fit of the data receivec by the inversion recorvery experiment.
 

 A particle with a net spin can absorb a photon with frequ. of f. f depends on the gyramgnetic ration gamma.

\(f = \gamma * B\), B: Magnetic Field

Nuclei have a nuclear spin quantum number I, which can take on 2I+1 orientations. Those spin states are split, if an external magnetic field is applied and the splitting between those states is specific for every nucleus.

The process where a lot of small magnets are used to build up small magnetic fields in order to make the main magnetic field as homogenous as possible.

At thermal equilibrium there is a net Magnetization Mo in the z-direction. Upon applying a 90 ° pulse, the Mo is rotated into the xy-plane. The magnetization then precesses in the x-y-plane and returns to the z-axis. A receiver records the oscillation signal on the y-axis, which decays in an exponential fashion.

The FID can be fourier transformed to obtain the frequency spectrum.
 

If we want to obtain optimal data, we need to calibrate the 90 ° pulse to maximize the performance. This is found by finding the 180 ° pulse, which corresponds to a null signal and is therefore easier to find. The 90 ° pulse then corresponds to the half of the 180 ° pulse.

The correlation between protons. In other words, we can detect which protons couple with each other.

Before the FID is fourier transformed, we can make some changes in order to improve the S/N ratio.

By a applying a negative LB factor we achieve to get sharper peaks with the price of having a lower S/N ratio.

Intensity vs. frequency.
 

The electron-correlationeffects

These methods calculate from the very beginning and use only very fundamental physical constants.

In quantum chemistry molecular orbitals are approximated by a linear combination of basis functions. For conveniance molecular orbitals are described as a linear combination of atomic orbitals. There are two important basis functions: slater type orbitals and Gaussian type orbitals (better for calculations)

STO functions are closer to reality, since they have cusps when the nucleus is approached, but the computing time for STOs is much longer.

The basis set of 3-21G represents, that 3 Gaussian functions are contracted to describe the inner shells and the valence shell is described by a contraction of 2 Gaussian functions and of 1 Gaussian function

Polarization functions account for a correction for the charge distribution within the molecule. So if we want to calculate the dipole moment of a molecule, we need to use polarization functions. They are shown by an asterisk, e.g. 6-31G*

Diffuse functions are used to describe electrons, which are weakly bonded, like for example electrons in anions.

SCF (self consistent field, Hartree-Fock-Method) does not consider electron-correlation.

spin correlation: electrons with the same spin avoid to meet each other

electron correlation: repulsive coulomb interaction between the electrons in a quantum mechanical system.

\(H = T_{Nuc} + T_{el} + E_{Nuc-el} + E_{Nuc-Nuc} +E_{el-el}\)

An electrochemical cell where a spontaneous chemical reaction is used to generate an electric current.

A galvanic cell is composed of two compartements, which are separated by a semipermeable membrane, which allows ions to permeate. The two compartements contain two different metal rods, which are connected through a wire.
 

\(\Delta G=\Delta H-T\Delta S\)

\(\Delta G=-n*E*F\)

Ist eine Primärzelle, d.h. nicht wiederaufladbar.

Red. \(Ag_2O+H_2O+2e^- \rightarrow2Ag+2OH^-\)

Ox. \(Zn \rightarrow Zn^{2+} + 2e^-\)