The rotationaltorsional spectrum of methanol Rogier Braakman Caltech
The rotational-torsional spectrum of methanol Rogier Braakman, Caltech John Pearson, JPL Brian Drouin, JPL Geoff Blake, Caltech
Motivation and Goals • Commissioning of Herschell and Sofia – – – • Map uncharted THz regions between 480 GHz and 5 THz Spectra of “known” molecules in ISM need to be characterized; methanol one of the most abundant Vt=0, 1, 2 all observed in ISM Pure spectroscopic interest – – – Rotation-Torsion interaction: lines everywhere! Extend assignments in Vt=0, 1, 2, include more DK information Assign Vt=3, 4 and vibrational states where energy levels are available
History • Previous global analyses including Vt=0, 1 and 2 – – Limited in J and K Neglected most Tu. FIR lines (eg. Matsushima et al. ) Ignored most Baskakov et al. GS lines New data from Tsunekawa et al. not included Refs: Belov et. al. 1995, Odashima et al. 1995, Xu & Lovas 1997 • Energy levels up to J=45 and K=14 from Microwave, IR & FIR spectra – Predictions not to microwave accuracy Ref: Moruzzi et. al. 1995, Methanol Atlas
HIFI Spectrum: • 452 – 485 GHz • Room temp, cold load • Lots of U-lines
New data • Almost continuously from 355 -1200 GHz plus regions around 1. 6 and 1. 8 THz • Lines up to J~45, K~15 -16 in GS • States through Vt=4, VCO+Vt=1 and Vri • Many, many new lines!
K=19 -18 a. R-branch region
Excited state transitions Vt=4, K=0 Vt=4, K=4 VCOVt=1, K=0 Vri, K=3 VCO, K=5
Vt=2, K=4 -3 Q branch
Analysis • Eventually global fit describing all interactions • Mean time: Check assignments, debug line files • Power series fitting: – Treat as rigid rotor – K-stacks as vibrational states – A and E states separately • Vt=0, A state underway: – 1500+ lines in fit, up to J=45, K=14 – K=9 problematic at high J • E state more problematic: – K-stack crossings
Summary • Extensive new spectral database • Assignments in ground and many excited states (Vt=0, 1, 2, 3, 4, VCO+Vt=0, 1, Vri) – Locating b-types – Mapping level crossings • Fitting of ground state underway, to be followed by Vt=1, 2, 3, ….
Thanks Group members: • • Dan Holland Vadym Kapinus Matthew Kelley Susanna Widicus Weaver HIFI spectrum: • David Teyssier • Claudia Comito Funding: • NASA • NSF