Lab Reports - Last Experiments
General comments. You do not have to prepare a formal lab report for either of these
experiments. Your informal report will include the data analysis, including, where
appropriate, error analysis, comparison with literature values, and discussion of any of
the points mentioned below.
HCl spectrum
1) Data will be shared among the members of the groups that did the experiment. The
data are the absorption spectra with peak locations.
2) Begin by making a table of peak assignments and locations for the 1H35Cl and 1H37Cl
isotopic species of HCl. Assignments should indicate the value of J in the v"=0 state, and
whether it is a P or an R branch transition (so, for example, P(3) or R(5)). Give the peak
locations in cm-1 (wavenumbers).
a) The two peaks on either side of the central gap in the spectrum are R(0) (high
energy side) and P(1) (low energy side).
b) Each HCl peak is actually a double peak, because of the presence of 1H35Cl and
H Cl. The higher intensity peak is the 1H35Cl peak (and it is located at a slightly higher
energy than the corresponding 1H37Cl peak).
1
37
3) Assign values for m to each transition. Recall that m = J" + 1 for the R-branch
transitions, and m = - J" for the P branch transitions. You should include the values of m
in your table of peak assignments and locations.
4) Data for each isotopic form of HCl will be separately fit to equn 9
(m) = 0 + (2Be - 2e) m - e m2
where 0, e, and Be are all in units of cm-1. This will mean fitting this equation to a
second order polynomial
y = a0 + a1 x + a2 x2
x=m
y = (m) (peak location, in cm-1)
Comparison of equn 9 to the third order polynomial coefficients allows us to make the
following identifications.
a2 = - e
a1 = (2Be - 2e)
a0 = 0
Find values for a0, a1, and a2 for both 1H35Cl and 1H37Cl, along with the 95% confidence
limits for your coefficients.
5) Comparison of the above two equations will now allow you to find the values for 0,
e, and Be, and the uncertainties in these values at the 95% confidence limits. Pay
attention to propagation of error.
6) Compare your experimental values for 0, e, and Be for 1H35Cl with the literature.
You may find literature values at the NIST website
http://webbook.nist.gov/chemistry/form-ser.html
Note that the electronic state is the ground electronic state, labeled X1+ in the NIST
table. Also note that you will have to calculate a literature value for 0 using equn 8
0 = e - 2 exe
7) Check to see how closely your coefficients for 1H37Cl obey the relationships given in
equn 11 and equn 13. For the comparison in equn 13 use 0 instead of e, since you do
not have enough information in your experimental results to determine e.
Molecular orbital calculations (Handout)
1) Do the molecular orbital calculations for the diatomic molecule for which you did the
literature search last semester. That way way, you will already have experimental and
theoretical literature values to compare your results with. If you do not have a diatomic
molecule ask that one be assigned to you.
2) To get to the screen where you will input the data for the calculation (page 5 of the
handout) click FILE---New.
3) Enter the following information
% Section
Leave blank
Route Section
#hf/6-31g* opt freq
#mp2/6-31g* opt freq
#b3yp/6-31g* opt freq
Title section
You need to put something here or the program will not run
So, for example, you could put the kind of calculation (HartreeFock, Moller-Plesset, or Density functional)
Hartree-Fock
Moller-Plesset
Density functional
Charge and multiplicity
Charge - the charge of your diatomic (will be 0)
Multiplicity - 1 (if singlet), 2 (if doublet), 3 (if triplet)...
If you don't know this, go back to your literature search results
In the section for Molecule Specification enter the data in the same was as in the handout.
Li
H1R
R=1.30
This means the following
Li - identifies the first atom in the diatomic
H 1 R - identifies the second atom in the diatomic, and tells the program to look
for a starting value for R.
blank line R=1.30 - The starting value for R to be used by the program (in Å, angstroms; 1
nm = 10 Å).
For your trial value for R you can use the experimental value for re from the
literature search, rounded to two significant figures. The program will vary the geometry
until it find re, the equilibrium bond distance. The trial value you put for R doesn't matter
as long as it is reasonably close to the true value for re.
4) After entering the data, click RUN (upper left side of the screen). The program will
ask for a file name. I would suggest you use your name and an abbreviation for the type
of calculation (joenshf, for example, if I did a Hartree-Fock calculation).
5) It will take about a minute for the program to run, and it will give you a large amount
of information. The three things you need are re (equilibrium bond distance) and e
(harmonic frequency), and the cpu time required for the calculation (a measure of how
long it takes the program to carry out the calculation). These can be found near the
bottom of the output file, and will look like the example on pages 7-8 of the handout.
6) Make a table that includes the values for re, e, and cpu time for your three
calculations, and the experimental values from your literature search.
7) Briefly discuss your results.
experiment.
Focus on which method seems to best agree with