112
EINSTEIN ON
PHOTOCHEMICAL EQUIVALENCE
cided whether
a
particular
effect had
to be
explained
by a
quantum property
of
radi-
ation
or
of
matter.
Einstein's
explanation
of
the
photoelectric
effect
by a quantum
property
of
radiation,
for
instance,
was
challenged
by
Arnold Sommerfeld's claim that
resonance
phenomena
within
the atom
play a
role.[18]
A
similar alternative
presented
itself
in the
case
of
photochemical
reactions, and
Einstein's
original
treatment
did
not
exclude
the
possibility
that
it
was
the
characteristic
frequency
of the
absorbing
mol-
ecules rather than
the
frequency
of
the
incoming
radiation that
matters.[19] He filled
this
gap
with
a
supplement
to his
paper,
Einstein
1912f (Doc. 5),
in which
he
analyzed
the
case
that
a
molecule
can
react to
a
finite
range
of
incoming
frequencies.[20]
An
additional stimulus for
the
theoretical
study
of this
problem
was
provided
by
War-
burg's
recent
experimental
research
on
ozone,
which
he
found
to
display
such
a
finite
range
of
sensitivity.[21]
In his
paper
Einstein assumed that
the
total number of decom-
posed
molecules
is equal
to the
sum
of
those
decomposed
by
the
individual
frequencies
in
order
to
show
that
the
energy
absorbed
by a
molecular dissociation
process depends
only
on
the
frequency
of the radiation. Einstein
presented
his
results
and
carefully
expounded
the
various
assumptions
on
which
they
rest in
a
lecture
he
gave
to
the
Societe
francaise
de
physique on
27
March
1913.[22]
IV
One of
the
key
problems
left unresolved
by
Einstein's
treatment
was
the
question
of
whether Planck's radiation
law
could
be
related
to
photochemical
processes.[23]
Paul
Ehrenfest and Arthur Schidlof
explored
this
possibility independently
and
corre-
sponded
about their
ideas
with
Einstein.[24]
The derivation of Wien's radiation formula
in
Einstein 1912b
(Doc. 2) requires
the
existence of
an "improper" thermodynamic
equilibrium
in
which
the
temperature
of
the
substance
and the
temperature correspond-
ing
to the
incoming
radiation
density
are
different.
The
main
problem
for
extending
this derivation
beyond
the
Wien
range
to
a new
derivation of Planck's
law
was,
in
[18]For
a
discussion of
the
relationship
between
this
problem
and
Einstein's
study
of
pho-
tochemistry,
see
Einstein
to
Wilhelm
Wien,
17
May 1912
(Vol. 5,
Doc.
395).
For Einstein's
controversy
with
Sommerfeld,
see
also
Sommerfeld et
al. 1911
(Vol. 3,
Doc.
24),
and,
for
historical
comment,
Stuewer
1975,
pp.
58-60.
[19]See, e.g.,
Haber's
detailed remarks
in
Fritz Haber
to Einstein,
8
March
1912
(Vol.
5,
Doc.
368),
which
may
have
drawn Einstein's attention
to this
ambiguity.
[20]The
essential
idea of
the
paper
is
sketched
in
Einstein
to
Emil
Warburg,
after
25
April–
before
11
May 1912
(Vol.
5,
Doc.
386).
[21]For
evidence
that
Warburg
communicated his
findings
to Einstein,
see
Einstein
1912f
(Doc. 5),
p.
881.
See
also Einstein
to
Emil
Warburg,
25
April
1912
(Vol. 5,
Doc.
385).
[22]See
Einstein
1913a
(Doc.
12)
for
its
published
version.
[23]For
Einstein's
early
interest
in this
question, see
Einstein
to
Michele
Besso, 26
March
1912
(Vol. 5,
Doc.
377).
[24]See Paul
Ehrenfest
to Einstein,
before
3 April
1912
(Vol. 5,
Doc.
380);
Einstein
to
Arthur
Schidlof,
17
June
1913
(Vol. 5,
Doc. 446);
and Einstein
to
Arthur
Schidlof,
5
July 1913
(Vol.
5,
Doc. 449).
Previous Page Next Page