a system, then the energy calculated
cannot be lower than the actual
energy of the ground state of the
system. To use variational principles
effectively in quantum mechanics
a trial wave function contains parameters that can be varied, with
these parameters being changed
until the lowest possible energy is
found.
Vaseline See petroleum jelly.
verdigris A green patina of basic
copper salts formed on copper. The
composition of verdigris varies
depending on the atmospheric
conditions, but includes the basic
carbonate CuCO 3 .Cu(OH) 2 , the basic
sulphate CuSO 4 .Cu(OH) 2 .H 2 O, and
sometimes the basic chloride
CuCl 2 .Cu(OH) 2 .
vermiculite See clay minerals.
very high frequency (VHF) A
radio frequency in the range 3 ×
10
8
– 0.3 × 10
8 Hz, i.e. having a wavelength in the range 1–10 m.
very low frequency (VLF) A radio
frequency in the range 3 × 10
4 – 0.3 ×
10
4 Hz, i.e. having a wavelength in
the range 10–100 km.
vibrational relaxation A process
in which a polyatomic molecule in
an excited vibrational state returns to
a lower vibrational state in the same
electronic state by colliding with
other molecules.
vibrational spectroscopy The
spectroscopic investigation of the vibrational energy levels of molecules.
In the infrared region of the electromagnetic spectrum vibrational transitions are accompanied by rotational
transitions. Infrared spectra of molecules are series of bands, with each
band being associated with a vibrational transition and every line in
that band being associated with a rotational transition that accompanies
the vibrational transition.
Some features of vibrational spectra can be analysed by regarding the
vibrations as simple harmonic motion, but a realistic account of molecular vibrations requires that
anharmonicity is taken into
account.
A diatomic molecule can only have
a vibrational–rotational spectrum if it
has a permanent dipole moment. A
polyatomic molecule can only have a
vibrational–rotational spectrum if
the normal modes of vibration cause
the molecule to have an oscillating
dipole moment.
vicinal (vic) Designating a molecule
in which two atoms or groups are
linked to adjacent atoms. For example, 1,2-dichloroethane (CH 2 ClCH 2 Cl)
is a vicinal (or vic) dihalide and can
be named vic-dichloroethane.
Victor Meyer’s method A
method of measuring vapour density,
devised by Victor Meyer (1848–97). A
weighed sample in a small tube is
dropped into a heated bulb with a
long neck. The sample vaporizes and
displaces air, which is collected over
water and the volume measured. The
vapour density can then be calculated.
villiaumite A mineral form of
sodium Ûuoride, NaF.
vinegar A dilute solution of
*ethanoic acid (up to 6%), used as a
Ûavouring and pickling medium. Natural vinegar is made by the continued fermentation of alcoholic
liquors, usually by Acetobacter species,
which oxidize ethanol to ethanoic
acid. Vinegar is also made by diluting
synthetic ethanoic acid.
vinyl acetate See ethenyl
ethanoate.
vinylation The catalysed reaction
Vaseline
546
v
www.AzShimi.ir www.AzShimi.com
cannot be lower than the actual
energy of the ground state of the
system. To use variational principles
effectively in quantum mechanics
a trial wave function contains parameters that can be varied, with
these parameters being changed
until the lowest possible energy is
found.
Vaseline See petroleum jelly.
verdigris A green patina of basic
copper salts formed on copper. The
composition of verdigris varies
depending on the atmospheric
conditions, but includes the basic
carbonate CuCO 3 .Cu(OH) 2 , the basic
sulphate CuSO 4 .Cu(OH) 2 .H 2 O, and
sometimes the basic chloride
CuCl 2 .Cu(OH) 2 .
vermiculite See clay minerals.
very high frequency (VHF) A
radio frequency in the range 3 ×
10
8
– 0.3 × 10
8 Hz, i.e. having a wavelength in the range 1–10 m.
very low frequency (VLF) A radio
frequency in the range 3 × 10
4 – 0.3 ×
10
4 Hz, i.e. having a wavelength in
the range 10–100 km.
vibrational relaxation A process
in which a polyatomic molecule in
an excited vibrational state returns to
a lower vibrational state in the same
electronic state by colliding with
other molecules.
vibrational spectroscopy The
spectroscopic investigation of the vibrational energy levels of molecules.
In the infrared region of the electromagnetic spectrum vibrational transitions are accompanied by rotational
transitions. Infrared spectra of molecules are series of bands, with each
band being associated with a vibrational transition and every line in
that band being associated with a rotational transition that accompanies
the vibrational transition.
Some features of vibrational spectra can be analysed by regarding the
vibrations as simple harmonic motion, but a realistic account of molecular vibrations requires that
anharmonicity is taken into
account.
A diatomic molecule can only have
a vibrational–rotational spectrum if it
has a permanent dipole moment. A
polyatomic molecule can only have a
vibrational–rotational spectrum if
the normal modes of vibration cause
the molecule to have an oscillating
dipole moment.
vicinal (vic) Designating a molecule
in which two atoms or groups are
linked to adjacent atoms. For example, 1,2-dichloroethane (CH 2 ClCH 2 Cl)
is a vicinal (or vic) dihalide and can
be named vic-dichloroethane.
Victor Meyer’s method A
method of measuring vapour density,
devised by Victor Meyer (1848–97). A
weighed sample in a small tube is
dropped into a heated bulb with a
long neck. The sample vaporizes and
displaces air, which is collected over
water and the volume measured. The
vapour density can then be calculated.
villiaumite A mineral form of
sodium Ûuoride, NaF.
vinegar A dilute solution of
*ethanoic acid (up to 6%), used as a
Ûavouring and pickling medium. Natural vinegar is made by the continued fermentation of alcoholic
liquors, usually by Acetobacter species,
which oxidize ethanol to ethanoic
acid. Vinegar is also made by diluting
synthetic ethanoic acid.
vinyl acetate See ethenyl
ethanoate.
vinylation The catalysed reaction
Vaseline
546
v
www.AzShimi.ir www.AzShimi.com