Lab Reports - Last Three Experiments
General comments. You do not have to prepare a formal lab report for any 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.
Dye spectrum
1) Data will be shared from the group that did the experiment. The only data are the
absorption spectra, from which the wavelength of peak absorbance and absorption
coefficient at the peak can be determined.
2) The dye molecules are pictured below. Remember that p is the number of carbon
atoms between the two nitrogen atoms and that N, the number of pi-electrons in the
conjugated chain, is p + 3.
3) The data analysis generally follows that given in the book. However, I would like you
to choose  = 0 in your calculations (that is, not use it as an adjustable parameter to
improve the agreement between theory and experiment).
4) Make sure to discuss the agreement (or lack of agreement) between the experimental
and calculated values for max for the dye molecules. Include a discussion of qualitative
agreement (trends in the data) and quantitative agreement (experimental vs model peak
wavelength).
HCl spectrum
1) Data will be shared from the group that did the experiment.
absorption spectra with peak locations.
The data are the
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).
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 will be fit to Eq. 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)
Also find 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.
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 Eq. 8
0 = e - 2 exe
7) Check to see how closely your coefficients for 1H37Cl obey the relationships given in
Eq. 11 and Eq. 13. For the comparison in Eq. 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, so the trial value you put for R doesn't
matter (except that if you put something far from the true value for re it will take longer
for the program to find the minimum in the potential).
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 two things you need are re (equilibrium bond distance) and e
(harmonic frequency). Both of 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 and e for your three calculations, two
calculations taken from the literature, and two experimental values.
7) Briefly discuss your results. Focus on which method seems to best agree with
experiment. You should also look at whether your calculations do a better or worse job
than the literature calculations in finding re and e.