High Resolution FIR and IR Spectroscopy of Methanol Isotopologues

1. High Resolution FIR and IR Spectroscopy of Methanol Isotopologues R.M. Lees, Li-Hong Xu Centre for Laser, Atomic and Molecular Sciences (CLAMS) Department of Physics, University of New Brunswick D.R.T. Appadoo, B. Billinghurst Canadian Light Source, University of Saskatchewan

2. May 14 – Launch of Herschel Space Observatory with HIFI - Heterodyne Instrument for the Far-Infrared • Herschel reached L2 Lagrange point in mid-July • HIFI was switched off on Aug 3 – anomaly!

3. Herschel PACS View of Galaxy M51 – June 14

4. Background and Motivation • The Herschel Space Observatory with the HIFI THz spectrometer on board was launched on May 14 and ALMA is coming – extensive methanol astronomical spectra are imminent and new lab data and insights are needed for all of the isotopic species of this principal "interstellar weed" to construct extensive databases and permit reliable modelling for astrophysical conditions. • The large-amplitude internal rotation in CH3OH makes the torsion-vibration energy manifold both complex and interesting, with strong torsion-mediated interactions coupling the different vibrational modes and several unassigned families of substates. • By looking at the isotopologues in detail, we hope for a new VISTA into the vibrational structure [Vibrational Isotopic Shift Technique for Assignment] with further clues to the vibrational identification.

5. n12=2 n12=1 V3 Etor = F<Pg2> + V3/2 <1- cos3g> H O 13C n12=0 H 0E 0A H H K values Methanol 1-D Large-Amplitude Torsion The torsional energies follow oscillating curves as a function of rotational quantum number K, with A and Etorsional symmetry.

6. 1500 1400 1300 1200 1100 1000 900 800 700 600 500 400 300 A 200 E1 t 100 E2 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Torsional-K-Rotational Energy Structure for CH3OH Lowest Small Amplitude Vibrations nt= 3 (0,15)/(1,13)/(2,11)A(1,10)/(2,7)A(0,12)/(1,9)E(0,9)/(1,5)A (nt,K)TSLevel crossings nt= 2 nt= 1 V3= 373.59 cm-1 nt= 0 K Values

7. (vt, K) rQ[(2,5)-(0,4)E] rQ[(3,-10)-(1,-9)E] rR[(2,14)-(0,13)E] pP[(2,2)-(0,3)A-] rR[(2,13)-(1,12)A] rR[(3,11)-(2,10)E] FIR Spectrum of CH3OH - New High Torsional Assignments

8. 93-101 E2 ??? 113-120 E1 64-52 E1 103-92 E1 24-12 E1 FIR Spectrum of CH3OH – Loomis-Wood Approach 74-62 A 14-23 A 34-22 A 142-130 E2

9. Origins of new torsional subbands of CH3OH

10. THz Interstellar Lines are Predicted from FTIR Combination Differences 113 502.48 687.73 121 111 60.11 ~ 1.8 THz 120 Kvt 125.14 (Moruzzi et al.)

11. Torsional combination bands Description nobs / cm-1 A' n1 OH stretch 3682 n2 CHasym stretch 2999 n3 CH sym stretch 2844 n4 CH3 asym bend 1478 n5 CH3 sym bend 1455 n6 OH bend 1340 n7 CH3 in-plane rock 1075 n8 CO stretch 1034 A" n9 CH asym stretch 2970 n10 CH3 o-o-p bend 1465 n11 CH3 o-o-p rock1145 n12 CH3 torsion 272 Vibrational modes of methanol Wavenumbers from A. Serrallach, R. Meyer and Hs. H. Gunthard, J. Mol. Spectrosc. 52 (1974) 94-129.

12. CLS FTIR Spectra of 13CH3OH and CD3OH 13CH3OH CH3 in-plane rock OH bend CO stretch CD3 in-plane rock CD3 bend CD3OH

13. Multiplet Structure in the O-18 CO-Stretch Band CH318OH CO-Stretch P(17) P(16) P(15) P(14) P(13) P(12) P(11) P(10) P(9) P(12) vt=1 vt=0 P(13) (vt,K)=(1,-3)E P(14)

14. vt = 1←0 ri vt = 0←1 oh ab sb "U" Subbands CH3 Bends CO Stretch Out-of-plane Rock 3E -8E 6E -5E 8A 7E 7A 4A 3A 7A 3A In-plane Rock OH Bend CLS FTIR Spectrum of O-18 Methanol

15. OH bend, vt = 0 OH bend, vt = 1 In-plane rock, vt = 1-0 U0 subband Loomis-Wood Plot for Line Series Identification

16. K-Reduced Torsion-Vibration Energy Map Connect the Dots??? K-Reduced Energy (cm-1) K Value

17. O-18 K-Reduced Torsion-Vibration Energy Map (sensitive to DK = 0 anharmonic perturbations) U2 substates OH bend, vt = 1 U1 substates CH3 asym bend, vt = 0 CO stretch, vt = 2 U0 substates OH bend, vt = 0 K-Reduced Energy (cm-1) In-plane rock, vt = 1 CO stretch, vt = 1 Out-of-plane rock, vt = 0 In-plane rock, vt = 0 CO stretch, vt = 0 K Value

18. CH3 in-plane rock Level-Crossing Resonances J-Reduced Energy (cm-1) CO stretch CH3 o-o-p rock J Value O-18 J-Reduced Rot-Tor-Vib Energy Map (sensitive to level-crossings and J-localized perturbations) O-18 CO Stretch - R.M. Lees, Reba-Jean Murphy, Giovanni Moruzzi, Adriana Predoi-Cross, Li-Hong Xu, D.R.T. Appadoo, B. Billinghurst, R.R.J. Goulding and Saibei Zhao,J. Mol. Spectrosc. 256, 91-98 (2009).

19. Summary • New highly excited torsional subbands have been assigned in the FIR spectrum of normal CH3OH locating 6 new substates for vt = 2, 9 for vt = 3, and 5 for vt = 4 at high K-values, providing predictions for potential THz astronomical lines from combination differences and important new torsional constraints for future global fitting of the ground vibrational dataset. • Vibrational bands have been recorded for the CO-stretching, CH3-rocking, OH-bending and CH3-bending modes of 13CH3OH, CH318OH and CD3OH. • The K- and J-reduced energy plots of CH318OH show complex mixtures of fundamental and torsional combination states with torsion-mediated intermode interactions that perturb the regular subband patterns, plus U substates of as yet unconfirmed vibrational parentage. • Isotopic shifts in subband origins and B-values suggest the U states are torsion-rocking combination states, possibly mixed with the OH-bend.