1. pgopher in the Classroom and the Laboratory http://pgopher. chm. bris
Colin M. Western
School of Chemistry, University of Bristol, Bristol BS8 1TS, UK

2. What does PGOPHER do?
Two distinct modes
Simulates rotation structure of molecular spectra:
Linear molecules, symmetric and asymmetric tops
Includes many effects (electron and nuclear spin, electric and magnetic fields).
Standard rotational Hamiltonians
Vibronic structure associated with an electronic state
Franck-Condon factors
Force Field calculations
Graphical user interface
Open source, freely downloadable from website
Windows, Mac and Linux versions
Does not require installation

3. Undergraduate practical – HCl IR spectrum
Low resolution IR spectrum from NIST website in JDX format
Demonstrates basic interactive fitting taking line positions from spectrum
Short lines join obs to calc
Experiment
Simulation
Right click here
to display line info
here
Right click and drag here
to put observed position
here

4. Interactive Adjustment of Parameters
Right Click
Roll mouse wheel

5. Adding another isotope – H35Cl and H37Cl
Starting from the previous data, a simulation showing both isotopes is easy to generate by copying and pasting the “Molecule” object
The constants and name can then be changed as required; here the abundance has been set to 1/3 and a small shift applied to the band origin

6. FTIR of Cigarette Smoke – Apparatus
Rough
Vacuum
Cigarette
FTIR gas cell
Requires spectrometer with ≤ 2 cm−1 resolution
Inspiration from N. Garizi, A. Macias, T. Furch, R. Fan, P. Wagenknecht and K.A. Singmaster, J. Chem. Ed (2001)
Developed with Nick Walker
Two stages
Taking spectrum (1 hour?)
Fitting spectrum (1-2 hours)

7. FTIR of Cigarette Smoke – Spectra
For typical student spectra, please contact:

8. FTIR of Cigarette Smoke – Fitting

9. FTIR of Cigarette Smoke – Support
Pre-Lab online quiz to help with doing calculations, mainly rotational constant to bond length
Multiple attempts allowed
Help with getting correct order of magnitude
Note precision of answers – ensures correct use of isotopic masses

10. Electronic Spectroscopy
Hollow Cathode Lamp: B2Σu+ – X2Σu+ emission in N2+
Lens −
Optical
Fibre N2 +
Camping Stove Flame
OH, CH, C2
USB4000 nm
Δ~50 cm−1
HR4000 nm
Δ~5 cm−1
HR4000 nm
Δ~5 cm−1
Fe Hollow cathode lamp
(from atomic absorption
instrument) – Ne/Fe
Ocean optics CCD spectrometers

11. Understanding Rotational Structure
Parallel C-H stretching band in CH3I
Calculate contour using E = BJ(J+1), I = (2J+1)exp(−E/kT)
(Only need K = 0)
Spreadsheet
Experiment
pgopher
2930
2940
2950
2960
2970
2980
2990
3000
3010
Wavenumber/cm-1

12. Perpendicular Bands in CH3I
C-H stretching region for CH3I
Stick spectrum using E(J, K=J), I = gJexp(−E(J,J)/kT)
Q branches only
E ΔK = ±1
A1 ΔK = 0
2950
3000
3050
3100
Wavenumber/cm-1

13. Hand out IR spectra of HF, H35Cl, D35Cl, H79Br…
Other possibilities
Group Exercise:
Hand out IR spectra of HF, H35Cl, D35Cl, H79Br…
For extra variation include 1-0, 2-0, 3-0 … bands (HITRAN)
Determine bond length from spectra, and look at trends
pgopher Vibrational Mode:
Determine bond force constants from vibrational frequencies (see Setting up a simple force field analysis for H2O on website)
Calculate Franck-Condon envelopes as a function of bond length/angle changes.
Large
Change in r
No Change in r
65000
70000
75000
65000
70000
75000