Colin M. Western School of Chemistry, University of Bristol, Bristol BS8 1TS, UK Recent Changes in PGOPHER: A General Purpose Program for Simulating Rotational Structure

Features in New Version from User Feedback Interactive adjustment of parameters with the mouse. Fits to combination differences. Uncertainties in calculated line positions can now be estimated from the results of least squares fitting. A separate nuclear spin temperature can be set, Tspin, to model the non equilibration of nuclear spin states on cooling, such as the ortho and para states in H 2. Alternative, simplified line list format. A command line version of PGOPHER is also now available, with text or Binary format output. Doppler double peak line shape, as often found in Fourier transform microwave spectroscopy. Initial hyperfine implementation for symmetric tops

Undergraduate practical – CO IR spectrum Low resolution IR spectrum of CO from cigarette smoke 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

Multiple states/species and Perturbations Non standard terms in the Hamiltonian, and perturbations can easily be added Example show inversion split ground state level of NH 3 Note Manifold (s) Containing two states, (0+ and 0-) and six extra terms acting within the manifold. These are J ± 6 which lift the degeneracy of K = 3 states

Combination differences Difference between (e.g) two transitions with same upper state is independent of upper state constants Input: Output (part): R(1) P(3) P(4) R(4) R(5) P(6) P(7) AutoCDLower Ignore Not common difference 1 observation(s) not converted to common differences Last unconverted observation at line 3 of obs.lin Residuals before fit for LinearMolecule for the Ground manifold Observed Calculated Obs-Calc StdDev P(3)/R(1) P(6)/R(4) P(7)/R(5) Directive

Line List Formats A variety of line list formats can be read; most flexible to use separate text file, rather than line list window. PGOPGER native – complete, but can be awkward if not generated using GUI Simplified format – suitable for many cases: Branch Format: Also reads SPFIT input files ( IncludeSPFIT directive), JPL catalogue files and HITRAN line lists. NQN Flagged by directive giving number of quantum numbers, here J, K a K c of asymmetric top P(2) P(1) R(0)

Alternative Lineshape - Doppler Split Peaks Doppler splitting ~ ±1.7×10 -6 ν often found in molecular beam microwave spectrometers Doppler setting splits each peak in two: Frequency/MHz Doppler = 1.68×10 -6, Lorentzian = 8 kHz Lorentzian = 8 kHz No Width Hyperfine structure in H 3 N-AgCl – see MH04, Nick Walker et al

Contour fitting to partly resolved structure Sub-Doppler spectra of NCO A-X electronic transition shows partly resolved hyperfine structure Fit below is direct to a fit to multiple experimental line profiles, rather than line positions Simulation/Fit Residual Plot

Tspin – nuclear spin temperature Equilibration of nuclear spin states often slow, (e.g. ortho/para in H 2 ) In PGOPHER characterize with spin temperature, Tspin defined so that ratio between total ortho states:total para states matches that at Tspin. e.g. NH 3 : three spin states, one with zero weight: Wavenumber/cm Wavenumber/cm -1 J,K = 1, 0 ← 0,0 J,K = 2, 1 ← 1,1 (Inversion split) Trot = 5K, Tspin=-1 (Equilibrated) Trot = 5K, Tspin= 300K

Stark and Zeeman effects Only requires dipole moment of state(s) of interest to be set. Matrix diagonalization approach used, including all states of a given M in basis; basis size set by Jmax e.g NH 3 : 2e6 V/m; Random polarization Zero Field

Molecular Focussing The “Levels” window allows the behaviour of levels as a function of external field to be plotted. Example is inversion split J=1, K=1 levels of NH 3

Features Calculates: Linear, Symmetric and Asymmetric top molecules Vibrational energy levels + Franck Condon factors (see TG13) Open and closed shell systems Microwave, infra-red, Raman and Multiphoton absorption and emission spectra Fitting to line positions or band contour Effects of external fields, predissociation and perturbations. All in an easy to use graphical interface: Used in undergraduate practicals as well as research work Interactively control fits and all simulation parameters Interactive help Wide selection of plot types and styles Overlay spectra from a variety of sources (both numbers and pictures) Please try the program. Feedback, both good and bad is very welcome. Acknowledgements Users, Bristol Laser Group, EPSRC, Royal Society To Do More example data files More than 2 equivalent nuclear spins Open Shell symmetric tops Spherical tops