colin m. western school of chemistry, university of bristol, bristol bs8 1ts, uk email :...
TRANSCRIPT
Colin M. Western
School of Chemistry, University of Bristol, Bristol BS8 1TS, UK
Email : [email protected]
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 H2.
• 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 hereto display line infohere
Right click and drag hereto put observed positionhere
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 NH3
• 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) 2926.1472P(3) 2822.8136 P(4) 2801.0182 R(4) 2983.1304 R(5) 3001.2369 P(6) 2756.3627 P(7) 2733.5398 AutoCDLower Ignore
Not common difference
1 observation(s) not converted to common differencesLast unconverted observation at line 3 of obs.linResiduals before fit for LinearMolecule for the Ground manifoldObserved Calculated Obs-Calc StdDev103.3336 103.0345 0.2991 1.4142 P(3)/R(1)226.7677 226.6760 0.0917 1.4142 P(6)/R(4)267.6971 267.8898 -0.1927 1.4142 P(7)/R(5)
Directive
Line List FormatsA 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 32 0 2 1 1 1 187.43463 1.01 1 0 1 0 1 21223.35986 1.02 1 1 2 0 2 22268.0897 1.0
Flagged by directive giving number of quantum numbers,here J, Ka Kc of asymmetric top
P(2) 996.0000 1.0P(1) 998.0000 1.0R(0) 1002.0000 1.0
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:
11913.70 11913.75 11913.80 11913.85 11913.90 11913.95Frequency/MHz
Doppler = 1.68×10-6, Lorentzian = 8 kHz
Lorentzian = 8 kHz
No Width
Hyperfine structure in H3N-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/FitResidual Plot
Tspin – nuclear spin temperature
• Equilibration of nuclear spin states often slow, (e.g. ortho/para in H2)
• In PGOPHER characterize with spin temperature, Tspin defined so that ratio between total ortho states:total para states matches that at Tspin.
• e.g. NH3: three spin states, one with zero weight:
0 10 20 30 40 50Wavenumber/cm-1
0 10 20 30 40 50Wavenumber/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 NH3:
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 NH3
http://pgopher.chm.bris.ac.uk
FeaturesCalculates:• 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.http://pgopher.chm.bris.ac.uk [email protected]
AcknowledgementsUsers, Bristol Laser Group, EPSRC, Royal Society
To Do• More example data files• More than 2 equivalent nuclear spins• Open Shell symmetric tops• Spherical tops