ΑΝΟΡΓΑΝΗ & ΑΝΑΛΥΤΙΚΗ ΧΗΜΕΙΑ Φασματοσκοπία Υπεριώδους- Ορατού (UV-Vis spectroscopy)

Φασματοσκοπία ή φασματοφωτομετρία Υπεριώδους- Ορατού: Ορισμός Φασματοσκοπία ή φασματοφωτομετρία Υπεριώδους- Ορατού: Φασματοσκοπία απορρόφησης (absorbance) ή ανάκλασης  (reflectance) στη φασματική περιοχή υπεριώδους- ορατού.

Electromagnetic spectrum h is Planck's constant: 6.626070040(81)×10−34J⋅s=4.135667662(25)×10−15eV⋅s ν is the frequency,  λ is the wavelength c is the speed of light= ~ 3.00×108 m/s

Absorption and color Grass and leaves appear green because chlorophyll absorbs wavelengths in the red and blue portion of the visible spectrum. The wavelengths in between (green) are transmitted.

Color of transition metal complexes When light passes through a solution containing transition metal complexes, we see those wavelengths of light that are transmitted. The solutions of most octahedral Cu (II) complexes are blue. The visible spectrum for an aqueous solution of Cu (II), [Cu(H2O)6]2+, shows that the absorption band spans the red-orange-yellow portion of the spectrum and green, blue and violet are transmitted.

Δεσμικά (bonding) και αντιδεσμικά (antibonding) μοριακά τροχιακά (molecular orbitals) ◆ Μόριο H2 Αντιδεσμικό τροχιακό Δεσμικό τροχιακό

Δεσμικά (bonding) και αντιδεσμικά (antibonding) μοριακά τροχιακά (molecular orbitals) ◆ Μόριο μεθανίου

Δεσμικά (bonding) και αντιδεσμικά (antibonding) μοριακά τροχιακά (molecular orbitals) ◆ Μόριο αιθενίου

HOMO and LUMO HOMO and LUMO are acronyms for highest occupied molecular orbital and lowest unoccupied molecular orbital, respectively. The energy difference between the HOMO and LUMO is termed the HOMO–LUMO gap. The difference in energy between these two frontier orbitals can be used to predict the strength and stability of transition metal complexes, as well as the colors they produce in solution.

Molecules containing π-electrons or non-bonding electrons (n-electrons) can absorb the energy in the form of ultraviolet or visible light to excite these electrons to higher anti-bonding molecular orbitals. The more easily excited the electrons (i.e. lower energy gap between the HOMO and the LUMO), the longer the wavelength of light it can absorb.

Types of electronic transitions σ, π and n electrons d and f electrons charge transfer electrons

Based on the fact of four type of transition- π-π. ,n-π. ,σ-σ. ,n-σ Based on the fact of four type of transition- π-π*,n-π*,σ-σ*,n-σ*.The energy required for various transitions obey the following order σ-σ*>n-σ*>π-π*>n-π*.

d and f electrons transitions

d-Orbital Splitting The magnitude of the splitting of the d-orbitals in a transition metal complex depends on three things: the geometry of the complex the oxidation state of the metal the nature of the ligands

The nature of the ligands

The nature of the ligands

The nature of the ligands

Quantitative analysis

Where A is absorbance (no units, since A = log10 P0 / P ) e is the molar absorbtivity with units of L mol-1 cm-1 b is the path length of the sample - that is, the path length of the cuvette in which the sample is contained, in cm. c is the concentration of the compound in solution, expressed in mol L-1

Molar absorptivity, ε electron jump Values for molar absorptivity can vary hugely. For example, ethanal has two absorption peaks in its UV-visible spectrum - both in the ultra-violet. One of these corresponds to an electron being promoted from a lone pair on the oxygen into a pi anti-bonding orbital; the other from a pi bonding orbital into a pi anti-bonding orbital. electron jump wavelength of maximum absorption (nm) molar absorptivity lone pair to pi anti-bonding orbital 290 15 pi bonding to pi anti-bonding orbital 180 10000 The ethanal obviously absorbs much more strongly at 180 nm than it does at 290 nm. (Although, in fact, the 180 nm absorption peak is outside the range of most spectrometers.)