Microwave Spectroscopy of the Excited Vibrational States of Methanol John Pearson, Adam Daly, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA USA Celina Bermúdez Grupo de Espectroscopia Molecular Universidad de Valladolid (Spain) Copyright All rights reserved.

Methanol ISMS 2015 Methanol is present in the Interstellar Medium Relevant molecule in atmospheric chemistry First detected in the early 70s High Abundance (detected the triple deuterated species) Involved in numerous atmospheric reactions It is used to measure the contamination levels TG03 John Pearson, Adam Daly, Celina Bermúdez

Methanol ISMS 2015 Internal rotation Simplest molecules with a C 3v internal rotation Much of internal rotation theory was developed and refined using Methanol as a test case Torsion: ν 12 = ν t ≅ 200cm -1 ν 8 = ν CO in-plane streching v t = 0, 1, 2 & 3 are well known Good starting point based on high IR term values Two previous attempts to analyze ν 8 (1033.5cm -1 ) RMS = 0.5cm -1 Missing or poorly characterized physics? Poor understanding of how to solve the problem? Bad data? ISMS 2015 TG03 John Pearson, Adam Daly, Celina Bermúdez

What is known? ISMS 2015 Well known vibrational structure Torsion mode ν t = ν 12 ~200cm -1 done in the ground manifold CO strech ν 8 = ν CO cm -1 Strong; complete energy levels: J=40, K=13 CH 3 in-plane rock ν 7 = ν ri cm -1 Weaker; many energy levels: J=35, K=8 CH 3 out-plane rock ν 11 = ν ro cm -1 Much weaker; only energy levels for larger K values OH bending ν 6 = ν OH cm -1 Most levels available Many combination with ν 12 also assigned ISMS 2015 TG03 John Pearson, Adam Daly, Celina Bermúdez ν 12 ν8ν8 ν6ν6 ν7ν7 ν 11 ν7ν7 ν7ν7

ν 12 ν8ν8 ν6ν6 ν7ν7 ν 11 ν7ν7 ν7ν7 Goals of the Effort 3.Analyze the first order interactions – Have ν 8 and 3 ν 12 a-type Coriolis (~8 GHz), b-type Coriolis (~370 MHz) – Have ν 8 and 4 ν 12 Fermi (2.5 cm -1 ) 4.Assess the relative importance of periodic vs non-periodic terms in the interactions 5.Fit the entire region with one model ISMS 2015 TG03 John Pearson, Adam Daly, Celina Bermúdez 1.Assign the microwave transitions of the known levels – Largely done still checking loops to verify all assignments 2.Find the missing levels of ν 7 and ν 11 to complete the picture – Lots of missing levels several are perturbed ν 12 = ν t (~200cm -1 ) ν 8 = ν CO (1033.5cm -1 ) ν 7 = ν ri (1074.5cm -1 ) ν 11 = ν ro (1145.0cm -1 ) ν 6 = ν OH (1339.5cm -1 )

We plan to use SPFIT, available at Transition identification Separate analysis of A and E Fittings for each K using power series B, D J, H J … for each K Analysis of the K-state interactions This method has been very successful at assignment but… Ultimately, we will need to unite into a common fit Strategy ISMS 2015 TG03 John Pearson, Adam Daly, Celina Bermúdez

Symmetry considerations Effective C s symmetry A’ : Even v numbers of ν 11 and ν t ν 8, ν 7 and ν 6 A’’ : Odd v numbers of ν 11 and ν t A’’ ↔ A’ : a- & b- type Coriolis A’ ↔ A’ : c-type Coriolis & Fermi A’’ ↔ A’’ : c-type Coriolis & Fermi E state selection rules: E1 ↔ E1 E2 ↔ E2 ISMS 2015 A state selection rules: Δ J=1 & ∆v t =0 → + ↔ + or - ↔ - Δ J=1 & ∆v t =1 → + ↔ - Δ J=0 & ∆v t =0 → + ↔ - Δ J=0 & ∆v t =1 → + ↔ + or - ↔ - ISMS 2015 TG03 John Pearson, Adam Daly, Celina Bermúdez

Allowed Non-Periodic Terms v t =3 8 v t = P α P a PαPaPαPa F, P c P a, P b F, P c P a, P b ISMS 2015 TG03 John Pearson, Adam Daly, Celina Bermúdez

Is C s a good symmeetry? Vibration makes modifications Mass of the Frame and/or the internal rotor POSSIBLE CHANGES IN THE BARRIER Internal rotation angle from PAM is unique for each vibration + torsion manifold Transforming to an Erkart system requires a rotation Torsional problem is unique in each vibration + torsion manifold Only one of the coupled states can be in an internal axis system (on diagonal P b =0 in CH 3 OH) ISMS 2015 In methanol internal axis is almost along the PAM a-axis so effects should be small, but torsion is large so effects might be visible. TG03 John Pearson, Adam Daly, Celina Bermúdez ν 12 ν8ν8 ν6ν6 ν7ν7 ν 11 ν7ν7 ν7ν7

New Assignments ν 11 A K=3-2 Q-branch ISMS 2015 TG03 John Pearson, Adam Daly, Celina Bermúdez

ν 12 ν8ν8 ν6ν6 ν7ν7 ν 11 ν7ν7 ν7ν7 Status of Assignments ISMS 2015 TG03 John Pearson, Adam Daly, Celina Bermúdez All ν 8 bands have been found to K=10 All IR assigned ν 7 and ν 11 bands have been found. Slowly filling in the missing bands – A-state ν 11 K=3-4 assigned, K=3-2 partly – Tentative a R branches for K=0 and K=1 of ν 11 – Several higher K ν 7 bands identified ν 12 = ν t (~200cm -1 ) ν 8 = ν CO (1033.5cm -1 ) ν 7 = ν ri (1074.5cm -1 ) ν 11 = ν ro (1145.0cm -1 ) ν 6 = ν OH (1339.5cm -1 )

ν 12 ν8ν8 ν6ν6 ν7ν7 ν 11 ν7ν7 ν7ν7 A-states interactions ISMS 2015 TG03 John Pearson, Adam Daly, Celina Bermúdez ν 12 = ν t (~200cm -1 ) ν 8 = ν CO (1033.5cm -1 ) ν 7 = ν ri (1074.5cm -1 ) ν 11 = ν ro (1145.0cm -1 ) ν 6 = ν OH (1339.5cm -1 )

ν 12 ν8ν8 ν6ν6 ν7ν7 ν 11 ν7ν7 ν7ν7 E-state interactions ISMS 2015 TG03 John Pearson, Adam Daly, Celina Bermúdez ν 12 = ν t (~200cm -1 ) ν 8 = ν CO (1033.5cm -1 ) ν 7 = ν ri (1074.5cm -1 ) ν 11 = ν ro (1145.0cm -1 ) ν 6 = ν OH (1339.5cm -1 )

ν 12 ν8ν8 ν6ν6 ν7ν7 ν 11 ν7ν7 ν7ν7 Missing Levels No missing levels in ν 8 below K=10 – All have been found in the spectrum ν 7 is missing K=7 and anything higher than 9 in the A state, ν 7 is missing K>3 in E1 and K<-5 in E2 ν 11 is missing K<4 in the A state ν 11 K<6 in both E-states ISMS 2015 TG03 John Pearson, Adam Daly, Celina Bermúdez ν 12 = ν t (~200cm -1 ) ν 8 = ν CO (1033.5cm -1 ) ν 7 = ν ri (1074.5cm -1 ) ν 11 = ν ro (1145.0cm -1 ) ν 6 = ν OH (1339.5cm -1 ) Many levels are highly mixed (hybridized) which gives rise to extra transitions or bands - ν 8 K=1 to v t =4 K=0 + was identified in the microwave - ν 8 K=5,6,7 are hybridized with ν 7 K=4,5,6 in the A-state - ν 8 K=-5 is hybridized with v t =3 K=-5 Many of these bands have been found as well - Intensity ratio give the degree of mixing

Next Steps Start characterizing ν 7 interaction with ν 8 Start characterizing ν 11 interaction with ν 8 Start characterizing ν 11 interaction with ν 7 Characterize to the extent possible v t =3 & 4 with ν 7 and ν 11. Complete matrix of interactions – Measure intensities to confirm degree of mixing Attempt to globally fit ISMS 2015 TG03 John Pearson, Adam Daly, Celina Bermúdez

Acknowledgement A part of this research was performed at the Jet Propulsion Laboratory, California Institute of Technology under a contract with the National Aeronautics and Space Administration ISMS 2015 TG03 John Pearson, Adam Daly, Celina Bermúdez