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

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

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

Interactive Adjustment of Parameters Right Click Roll mouse wheel

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

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. 78 1665 (2001) Developed with Nick Walker Two stages Taking spectrum (1 hour?) Fitting spectrum (1-2 hours)

FTIR of Cigarette Smoke – Spectra For typical student spectra, please contact: help-pgopher@bristol.ac.uk

FTIR of Cigarette Smoke – Fitting

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

Electronic Spectroscopy Hollow Cathode Lamp: B2Σu+ – X2Σu+ emission in N2+ Lens − Optical Fibre N2 + Camping Stove Flame OH, CH, C2 USB4000 180-890 nm Δ~50 cm−1 HR4000 395-485 nm Δ~5 cm−1 HR4000 303-400 nm Δ~5 cm−1 Fe Hollow cathode lamp (from atomic absorption instrument) – Ne/Fe Ocean optics CCD spectrometers

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

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

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

http://pgopher.chm.bris.ac.uk