home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Turnbull China Bikeride
/
Turnbull China Bikeride - Disc 2.iso
/
AVOGADRO
/
CHEMISTRY
/
ENERGY
/
!Energy
/
GraphHelp
< prev
next >
Wrap
Text File
|
1996-05-01
|
2KB
|
50 lines
PURE ROTATIONAL SPECTRA OF DIATOMIC MOLECULES
This part of the program simulates the pure
rotational spectrum of a diatomic molecule from
data entered by the user. The elementary treatment
of the relative intensities of absorption from the
Jth level assumes that they depend only on the
relative populations of rotational levels given by
the expression
N(J) = N(0)(2J + 1)exp(-BJ(J + 1)/kT)
The rotational constant B is calculated from the
data entered and the relative populations of the
energy levels are displayed graphically. In the
elementary treatment of the relative intensities
of absorption from the Jth level, it is assumed
that they depend only on the relative populations
of rotational levels given by the above expression
but this does not give good agreement with
experiment because of the neglect of a number of
factors. Better agreement with experiment is
obtained if the relative intensities of absorption
from the Jth level are calculated from
Int = Constant x exp(-BJ(J+1)/kT).(1 -
exp(-2B(J+1)/kT).(J+1)^2
The program compares the predicted intensity
distributions given by the two expressions as a
plot of intensity against frequency.
The upper bars are calculated using the more
accurate expression; the lower bars are derived
from the simple expression. The value of J shown
is for the rotational level from which absorption
occurs.
Remember that homonuclear diatomic molecules
cannot have a dipole moment, and would not
therefore show any absorption corresponding to a
pure rotational spectrum.
By default, the program does not show an intensity
graph when the masses of the two atoms are the
same. Only the relative populations of the
rotational levels are displayed. However, the
test can be overridden if you wish to see the
hypothetical intensities.