Merken

Oscillations of Molecules in Melamine Crystal Lattices with Hydrogen Bonds

Zitierlink des Filmsegments
Embed Code

Automatisierte Medienanalyse

Beta
Erkannte Entitäten
Sprachtranskript
The Raman and infrared spectra of molecules in the crystalline state show bands between 50 and 300 wave numbers, which disappear when the crystal dissolves or melts. These bands are caused by vibrations of the molecules about their positions in the lattice: Translational vibrations along the axes of the molecules and torsional vibrations (also called librations) about the axes of the molecules. Their frequencies are low, since the masses of the molecules are large, and the intermolecular elastic forces are small. The broad band in the Raman spectrum of melamine at 126 wave number is due to a libration. Here
you see a lattice plane in a melamine crystal. Four of the molecules are coloured. We shall now show vibrations, which are excited by one quantum of energy. We will first look at the vibrations
of two of these molecules.
The vibrational amplitudes are magnified
by a factor of ten.
The libration, a torsional vibration
about the horizontal y-axis, is
clearly visible. An internal molecular vibration, the out-of-plane deformation vibration
of the NH2-group, is coupled
with this lattice vibration. We
will now see the vibration
of all the molecules in
one plane. The strongest band in the Raman spectrum is however due to a translation vibration. Here is the translation
vibration in the direction of
the horizontal y-axis. The molecules
are moving an an antiparallel
sense. Now we can see
that chains of molecules are
moving in an antiparallel sense.
It is evident that the
hydrogen bonds, characterized by broken
lines, are stretched considerably. Translation
and libration can occur simultaneously,
as for example in this lattice vibration. During the translational vibration the centre of gravity of the moelcule moves in the direction of the vertical
axis. A libration about the
horizontal axis occurs simultaneously. We
shall now see the same
motions for all the molecules
in one layer of the
lattice. The lattice vibrations can
also be thermally excited: in
this manner the specific heat
of the crystals is stored.
Here you see the true
vibrational amplitudes of the thermally
excited lattice vibrations. At 60 Kelvin, the molecules move only slightly. These are the true
amplitudes at 300 Kelvin, that
is at room temperature. All
the different lattice vibrations are thermally excited. The mean amplitude
of the translational motion is
0,8 Ångström, or 80 pm,
that of the librations about four degrees. One can imagine,
that when the temperature is raised still further, the lattice
will collapse at the melting
point, that is for melamine at about 630 Kelvin.
VSEPR-Modell
Translationsfaktor
Kristall
Raman-Spektroskopie
Raman-Effekt
Raman-Effekt
Melamin
Molekül
Wasserwelle
Computeranimation
Kristall
Quantenchemie
Molekül
Computeranimation
Computeranimation
Sonnenschutzmittel
Computeranimation
Computeranimation
Deformierung
Computeranimation
Computeranimation
Computeranimation
Computeranimation
Computeranimation
Raman-Spektroskopie
Translationsfaktor
Raman-Effekt
Translationsfaktor
Computeranimation
Molekül
Computeranimation
Computeranimation
Sense
Computeranimation
Sense
Kettenlänge <Makromolekül>
Molekül
Computeranimation
Hydrierung
Computeranimation
Translationsfaktor
Computeranimation
Computeranimation
Computeranimation
Raman-Effekt
Translationsfaktor
Computeranimation
Computeranimation
Computeranimation
Bewegung
Molekül
Computeranimation
Computeranimation
Computeranimation
Kristall
Molwärme
Computeranimation
Computeranimation
Computeranimation
Molekül
Enhancer
Computeranimation
Computeranimation
Computeranimation
Bewegung
Computeranimation
Alkoholgehalt
Computeranimation
Auftauen
Körpertemperatur
Computeranimation
Computeranimation

Metadaten

Formale Metadaten

Titel Oscillations of Molecules in Melamine Crystal Lattices with Hydrogen Bonds
Alternativer Titel Schwingungen von Molekülen im Kristallgitter - Melamin mit Wasserstoffbrücken
Autor Schrader, Bernhard
Schneider, Richard
Lizenz CC-Namensnennung - keine kommerzielle Nutzung - keine Bearbeitung 3.0 Deutschland:
Sie dürfen das Werk bzw. den Inhalt in unveränderter Form zu jedem legalen und nicht-kommerziellen Zweck nutzen, vervielfältigen, verbreiten und öffentlich zugänglich machen, sofern Sie den Namen des Autors/Rechteinhabers in der von ihm festgelegten Weise nennen.
DOI 10.3203/IWF/C-1212eng
IWF-Signatur C 1212
Herausgeber IWF (Göttingen)
Erscheinungsjahr 1976
Sprache Englisch
Produzent IWF
Produktionsjahr 1975

Technische Metadaten

IWF-Filmdaten Film, 16 mm, LT, 68 m ; F, 6 1/2 min

Inhaltliche Metadaten

Fachgebiet Chemie
Abstract Translatory and torsional vibrations of the molecules. Using melamine for an example, the elastic properties of the intermolecular hydrogen bonds are demonstrated. Using the thermally induced vibrations at 60 and 300 K it is shown, that they are the mechanical storage means of the specific heat of the melamine crystal.
Schlagwörter molecular structure
oscillations / in molecules
specific heat
hydrogen bonding

Ähnliche Filme

Loading...