Thursday, July 9, 2015

HP Prime: Diatomic Molecules

HP Prime: Diatomic Molecules

Diatomic Molecules

The program DIATOMIC will calculate:

*  Distance from the center of mass for each molecule
*  Inertia of the molecule
*  Rotational Energy at level j  (j = 0, 1, 2, 3…)
*  Vibrational Energy at level n  (n = 0, 1, 2, 3…)

A diatomic molecule is a molecule made of two atoms.  Examples are H2, O2, NaCl (sodium chloride), and CO (carbon monoxide). 

Input:

*  Mass of the two molecules, in atomic mass units (u).  The program will convert them to kilograms.  The conversion is 1 u ≈ 1.660538921 * 10^-27 kg
*  Distance of the “bar” between the two molecules.  Give this in ångströms, which an ångström is 10^-10 m. 
*  Rotational and Vibrational Energy levels.  They do not have to be the same.
*  Frequency of the diatomic molecule in 10^12 Hz.  Typically, molecules and atoms exhibit frequencies in the order of 10^13 Hz.


The formulas are derived from the use of the Schrödinger Equation.  While I won’t give much details, a derivation can be found in many resources, such as this link:  http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Rotational_Spectroscopy/Rotational_Spectroscopy_of_Diatomic_Molecules

This program can be adopted to other graphing calculators, but here is a version for the HP Prime:

Program DIATOMIC

EXPORT DIATOMIC()
BEGIN
// EWS 2015-07-09
// Diatomic Molecule
LOCAL m1,m2,r,l1,l2,I;
LOCAL j,n,w;
LOCAL Er,Ev;

// Input
INPUT({m1,m2,r,j,n,w},
"Diatomic Molecule",
{"Mass 1:","Mass 2:",
"r:","J:","N:","freq:"},
{"Mass in atomic units",
"Mass in atomic units",
"Distance in Angstroms",
"Rotational energy level",
"Vibration energy level",
"Frequency (10^12 Hz)"});

// Integer Parts
n:=IP(n);
j:=IP(j);

// Convert to kg
m1:=m1*1.660538921ᴇ−27;
m2:=m2*1.660538921ᴇ−27;

// Convert Angstroms to m;
r:=r/1ᴇ10;

// Convert to Hz;
w:=w*1ᴇ12;

// Lengths
l1:=m2*r/(m1+m2);
l2:=m1*r/(m1+m2);

// Inertia:
I:=m1*l1^2+m2*l2^2;

// Rotational Energy:
Er:=1.054571726ᴇ−34^2/(2*I)*j*(j+1);

// Vibrational Energy:
Ev:=(n+1/2)*1.054571726ᴇ−34*w;

// Results
PRINT();
PRINT("Distance to Center (m):");
PRINT("From Mol. 1: "+STRING(l1));
PRINT("From Mol. 2: "+STRING(l2));
PRINT("Inertia:");
PRINT(STRING(I)+" kg m^2");
PRINT("Rotational Energy:");
PRINT(STRING(Er)+" J");
PRINT("Vibrational Energy:");
PRINT(STRING(Ev)+" J");

RETURN({l1,l2,I,Er,Ev});
  
END;
  
Example

Mass 1:  Hydrogen:  1.00794 u
Mass 2:  Chlorine:  35.4270 u
Distance:  6 ångströms
Frequency:  3.6 x 10^13 Hz


Input Screen:


Output Screen:


Energy:
Rotational:  approx. 1.90*10^-23 J
Vibration:  approx. 5.69*10^-21 J

Sources:

Strong, Benjamin.  “Rotational Spectroscopy of Diatomic Molecules”  http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Rotational_Spectroscopy/Rotational_Spectroscopy_of_Diatomic_Molecules   March 26, 2015.   Retrieved July 5, 2015.

Wikipedia.  “Atom Vibrations”  https://en.wikipedia.org/wiki/Atom_vibrations  Retrieved July 9, 2015.

Young, Hugh D. & Roger A Freedman   “University Physics with Modern Physics”  11th Ed.  Pearson:  San Francisco.  2003
  
Eddie

This blog is property of Edward Shore.  2015.

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