150
7.
THE OUTER PARTS OF THE ATOM
potentials for mercury between 4.9 volts and the ionizing potential
of 10.4 volts.
The existence of excitation potentials for the
atoms of other elements and for molecules has been established in
similar fashion.
The minimum excitation potential is called the resonance
potential VT.* Some values of V. will be found in Table 2 at
the end of this book.
It may be concluded that the electrons in
the atom may be shifted from their
normal state only into
deaiz‘e higher energy levels.
The collision between an electron and an atom may occur head
on
or at a glancing angle.
Hence, the type of collision may be
expected to determine whether or not the transition from a normal
state to a higher one will occur.
It can be shown9 that the probability that an atom will be excited is zero just at the value VI but
rises rapidly to a maximum as the energy of the bombarding elec- "
trons
is increased.
Beyond this maximum it decreases again.
The maximum is not displaced as far from VI as the maximum
probability ofionization is from the minimum ionizing potential
7—7.
Energy Levels—Radiation of Light.D‘E——VVhen an atom
absorbs energy equal to an excitation potential, one of its electrons
is raised to a denite higher energy level.
As the electron returns
to its normal level, the atom emits an amount of energy equal to
that which it absorbed.
This appears in the form of an electro—
magnetic radiation corresponding to one frequency or wave—length
in the x-ray, ultra—violet, visible or heat spectrum.
The energy
of the impinging electrons is then the same as the difference in
energy Æ —
between the two atomic states.
This voltage is
spoken of as the radiation potential (V).
The quantum theory states that the energy in each radiated
photon is equal to the difference of energies of the electron in the
atom.
Thus,
hu = (o‘Ê — (£.
(7—9)
where & is Planck’s constant (=6.547 >< 10—27) and v is the fre—
quency of the radiated light.
Instead of the frequency (V), the
wave—length (À) may be used; (>\ = 6/7}, where c is the velocity of
* In the case of mercury, the 4.9 value is not the resonance potential since &
meta-stable state exists at 4.6 volts.
7.
THE OUTER PARTS OF THE ATOM
potentials for mercury between 4.9 volts and the ionizing potential
of 10.4 volts.
The existence of excitation potentials for the
atoms of other elements and for molecules has been established in
similar fashion.
The minimum excitation potential is called the resonance
potential VT.* Some values of V. will be found in Table 2 at
the end of this book.
It may be concluded that the electrons in
the atom may be shifted from their
normal state only into
deaiz‘e higher energy levels.
The collision between an electron and an atom may occur head
on
or at a glancing angle.
Hence, the type of collision may be
expected to determine whether or not the transition from a normal
state to a higher one will occur.
It can be shown9 that the probability that an atom will be excited is zero just at the value VI but
rises rapidly to a maximum as the energy of the bombarding elec- "
trons
is increased.
Beyond this maximum it decreases again.
The maximum is not displaced as far from VI as the maximum
probability ofionization is from the minimum ionizing potential
7—7.
Energy Levels—Radiation of Light.D‘E——VVhen an atom
absorbs energy equal to an excitation potential, one of its electrons
is raised to a denite higher energy level.
As the electron returns
to its normal level, the atom emits an amount of energy equal to
that which it absorbed.
This appears in the form of an electro—
magnetic radiation corresponding to one frequency or wave—length
in the x-ray, ultra—violet, visible or heat spectrum.
The energy
of the impinging electrons is then the same as the difference in
energy Æ —
between the two atomic states.
This voltage is
spoken of as the radiation potential (V).
The quantum theory states that the energy in each radiated
photon is equal to the difference of energies of the electron in the
atom.
Thus,
hu = (o‘Ê — (£.
(7—9)
where & is Planck’s constant (=6.547 >< 10—27) and v is the fre—
quency of the radiated light.
Instead of the frequency (V), the
wave—length (À) may be used; (>\ = 6/7}, where c is the velocity of
* In the case of mercury, the 4.9 value is not the resonance potential since &
meta-stable state exists at 4.6 volts.