1 / 20

High-accuracy ab initio water line intensities

Dive into the study of water line intensities with a focus on achieving 1% accuracy, using variational methods and multi-reference techniques. Understand the importance, challenges, and solutions for accurate measurements.

vferguson
Download Presentation

High-accuracy ab initio water line intensities

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lorenzo Lodi University College London Department of Physics & Astronomy High-accuracy ab initio water line intensities

  2. Talk summary • Variational methods for vibration-rotation spectra • Electronic structure treatment • Results for water line intensities

  3. What we are aiming at? • Line intensities are extremely important. • They are also difficult to measure accurately. • Aim: accuracy of 1%(for majority lines). • We used the very best level of theory to achieve this goal. • Line intensities likely to be in error can be identified.

  4. General scheme of solution • Born-Oppenheimer approximation. • Solve the electronic problem, obtaining Potential Energy Surface E(R) and Dipole Moment Surface m(R). • Use E(R) for the motion of the nuclei. • From m(R) and nuclear-motion wavefunctions calculate line intensities.

  5. Solving for the nuclear motion • Molecule-fixed, J-dependent effective hamiltonians can be derived. • The resulting 3-dimentional Schrödinger equation can be solved numerically. • An efficient technique to do this is the Discrete Variable Representation method. • Accuracy of line positions and intensities is limited by quality of PES and DMS.

  6. Multi-reference methods • Standard methods such as DFT, MP2 etc are not suitable. • Multi-reference methods are needed. • We used IC-MRCI+Q[8,10], 6Z basis set. • Relativistic effects accounted for.

  7. Equilibrium water dipole From L. Lodi and J. Tennyson, J. Phys. B: At. Mol. Opt. Phys. 43, 133001 (2010)

  8. Fitting the points • Intensities are very sensitive to oscillations in the DMS.

  9. Lisak, Harvey and Hodges • D. Lisak, D. K. Harvey and J.T. Hodges, Phys. Rev. A 79, 052507 (2009) • 15 line intensities between 7170-7183 cm-1 • Declared error of 0.4%.

  10. Lisak, Harvey and Hodges • 15 very accurate lines • One line where theory is consistently stronger by 30% • For the other 14 lines: average 1.01(1)

  11. Ponsardin & Browell • P.L. Ponsardin and E. V. Browell, J. Mol. Spectr. 185, 58-70 (1997) • 40 line intensities around 12,200 cm-1. • Declared error of 2%.

  12. Summary comparison with HITRAN2008 • Total lines analysed: 26,957 • Stable lines: 19,056 • Unstable lines: 7,901 • Average of ratios for stable lines: 1.00(4)

  13. Final words • New high-accurate intensity linelist • Error of 1% in most cases • “Resonant” lines with large errors can be identified

More Related