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 para-
meters 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.
vermiculiteSee clay minerals.very high frequency (VHF)A
radio frequency in the range 3 ×
108 – 0.3 × 108 Hz, i.e. having a wave-
length in the range 1–10 m.
very low frequency (VLF)A radio
frequency in the range 3 × 104 – 0.3 ×
104 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 vi-
brational energy levels of molecules.
In the infrared region of the electro-
magnetic spectrum vibrational tran-
sitions are accompanied by rotational
transitions. Infrared spectra of mol-
ecules are series of bands, with each
band being associated with a vibra-
tional transition and every line in
that band being associated with a ro-tational transition that accompanies
the vibrational transition.
Some features of vibrational spec-
tra can be analysed by regarding the
vibrations as simple harmonic mo-
tion, but a realistic account of mo-
lecular 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 exam-
ple, 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 calcu-
lated.villiaumiteA mineral form of
sodiumÛuoride, NaF.vinegarA dilute solution of
*ethanoic acid (up to 6%), used as a
Ûavouring and pickling medium. Nat-
ural vinegar is made by the contin-
ued fermentation of alcoholic
liquors, usually by Acetobacter species,
which oxidize ethanol to ethanoic
acid. Vinegar is also made by diluting
synthetic ethanoic acid.vinyl acetateSee ethenyl
ethanoate.vinylationThe catalysed reactionVaseline 546v