High Resolution FIR and IR Spectroscopy of

Methanol Isotopologues

R.M. Lees, Li-Hong XuCentre for Laser, Atomic and Molecular Sciences (CLAMS)

Department of Physics, University of New Brunswick

D.R.T. Appadoo, B. BillinghurstCanadian Light Source, University of Saskatchewan

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!

Herschel PACS View of Galaxy M51 – June 14

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.

Methanol 1-D Large-Amplitude Torsion

O

H

H

H

13C

H

100

150

200

250

300

350

400

450

0 2 4 6 8 10 12K values

Etor = F<P2> + V3/2 <1-

cos3>

V3 12=1

12=00E0A

12=2

The torsional energies follow oscillating curves as a function of rotational quantum number K, with A and E torsional symmetry.

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

1500

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Torsional-K-Rotational Energy Structure for CH3OH

V3= 373.59 cm-1

AE1

E2

t= 0

t= 1

t= 2

t= 3

(0,15)/(1,13)/(2,11)A

(1,10)/(2,7)A

(0,12)/(1,9)E

(0,9)/(1,5)A

(t,K)TS

Level crossings

K Values

t

Lowest SmallAmplitudeVibrations

rQ[(2,5)-(0,4)E]rQ[(3,-10)-(1,-9)E] rR[(2,14)-(0,13)E]

(vt, K)

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

660.5 660.6 660.7 660.8 660.9 661.0 661.1 661.2 661.3 661.4 661.5 661.6 661.7 661.8 661.9 662.0 660.5 660.6 660.7 660.8 660.9 661.0 661.1 661.2 661.3 661.4 661.5 661.6 661.7 661.8 661.9 662.0

662.0 662.1 662.2 662.3 662.4 662.5 662.6 662.7 662.8 662.9 663.0 663.1 663.2 663.3 663.4 663.5 662.0 662.1 662.2 662.3 662.4 662.5 662.6 662.7 662.8 662.9 663.0 663.1 663.2 663.3 663.4 663.5

663.5 663.6 663.7 663.8 663.9 664.0 664.1 664.2 664.3 664.4 664.5 664.6 664.7 664.8 664.9 665.0 663.5 663.6 663.7 663.8 663.9 664.0 664.1 664.2 664.3 664.4 664.5 664.6 664.7 664.8 664.9 665.0

74-62 A14-23 A

34-22 A

142-130 E2

FIR Spectrum of CH3OH – Loomis-Wood Approach

64-52 E1 24-12 E1103-92 E1

93-101 E2

113-120 E1???

vt' vt" K' K" TS obs / cm-1 Olap El vt' vt" K' K" TS obs / cm-1 Olap El

2 0 11 10 A 420.03 0.0381 3 1 11 10 E2 584.87 -0.0520 2 0 13 12 E2 499.16 0.0951 3 1 12 11 E1 530.81 -0.0627 2 0 14 13 E1 473.62 0.1070 3 1 12 11 A 620.41 0.0113 2 0 15 14 A 454.48 0.1059 3 1 13 12 A 477.58 -0.0727 2 1 12 11 E1 436.58 -0.0527 3 2 9 8 E2 600.64 -0.0220 2 1 13 12 A 470.18 -0.0590 3 2 10 9 E2 414.62 -0.0197 3 0 10 11 E2 644.93 0.0283 3 2 10 9 E1 632.03 -0.0203 3 0 11 12 E1 687.73 0.0228 3 2 12 11 A 553.40 -0.0251 3 0 12 13 E1 579.10 -0.0035 4 2 2 1 E1 635.06 -0.0166 3 0 12 11 E1 738.64 0.0339 4 2 2 3 E2 631.50 -0.0151 3 0 13 12 A 703.13 0.0404 4 2 3 2 A 664.55 -0.0154 3 1 9 8 E1 686.69 -0.0395 4 2 6 5 E1 634.39 -0.0183 3 1 9 10 E2 690.74 0.0315 4 2 7 6 A 661.74 -0.0169 3 1 10 9 E2 518.29 -0.0294 4 3 1 2 A 661.37 -0.0141 3 1 11 12 E1 502.48 -0.0451 4 3 4 3 E2 694.41 -0.0144 3 1 11 10 E1 559.86 -0.0228

Origins of new torsional subbands of CH3OH

113

120

121

111

502.48687.73

125.14(Moruzzi et al.)

60.11 ~ 1.8 THz

THz Interstellar Lines are Predicted from FTIR Combination Differences

Kvt

Description obs / cm-1

A'1 OH stretch 3682

CH asym stretch 2999

CH sym stretch 2844

4 CH3 asym bend 1478

5 CH3 sym bend 1455

6 OH bend 1340

7 CH3 in-plane rock 1075

8 CO stretch 1034

A"9 CH asym stretch 2970

10 CH3 o-o-p bend 1465

11 CH3 o-o-p rock 1145

12 CH3 torsion 272

Vibrational modesof methanol

Wavenumbers from A. Serrallach, R. Meyer and Hs. H. Gunthard, J. Mol. Spectrosc. 52 (1974) 94-129.

Torsional combination bands

800 900 1000 1100 1200 1300 800 900 1000 1100 1200 1300

CLS FTIR Spectra of 13CH3OH and CD3OH

CD3OH

CO stretchOH bend

CD3 bend

CH3 in-plane rock

13CH3OH

CD3 in-plane rock

P(12)

P(13)

P(14)

P(17) P(16) P(15) P(14) P(13) P(12) P(11) P(10) P(9)

vt=1vt=0

Multiplet Structure in the O-18 CO-Stretch Band

(vt,K)=(1,-3)E

CH318OH CO-Stretch

900 1000 1100 1200 1300 1400 1500 1600 1700 900 1000 1100 1200 1300 1400 1500 1600 1700

CLS FTIR Spectrum of O-18 Methanol

CO Stretch Out-of-plane Rock

CH3 Bends

absb

vt = 1← 0 rivt = 0← 1 oh

"U" Subbands

1071.2 1071.4 1071.6 1071.8 1072.0 1072.2 1072.4 1072.6 1072.8 1073.0 1071.2 1071.4 1071.6 1071.8 1072.0 1072.2 1072.4 1072.6 1072.8 1073.0

In-plane Rock

3A-8E

4A 7A-5E6E3E

1340.5 1341.0 1341.5 1342.0 1342.5 1340.5 1341.0 1341.5 1342.0 1342.5

OH Bend

7A3A7E8A

1317.5 1317.6 1317.7 1317.8 1317.9 1318.0 1318.1 1318.2 1318.3 1318.4 1318.5 1318.6 1318.7 1318.8 1318.9 1319.0 1317.5 1317.6 1317.7 1317.8 1317.9 1318.0 1318.1 1318.2 1318.3 1318.4 1318.5 1318.6 1318.7 1318.8 1318.9 1319.0

1319.0 1319.1 1319.2 1319.3 1319.4 1319.5 1319.6 1319.7 1319.8 1319.9 1320.0 1320.1 1320.2 1320.3 1320.4 1320.5 1319.0 1319.1 1319.2 1319.3 1319.4 1319.5 1319.6 1319.7 1319.8 1319.9 1320.0 1320.1 1320.2 1320.3 1320.4 1320.5

1320.5 1320.6 1320.7 1320.8 1320.9 1321.0 1321.1 1321.2 1321.3 1321.4 1321.5 1321.6 1321.7 1321.8 1321.9 1322.0 1320.5 1320.6 1320.7 1320.8 1320.9 1321.0 1321.1 1321.2 1321.3 1321.4 1321.5 1321.6 1321.7 1321.8 1321.9 1322.0

Loomis-Wood Plot for Line Series Identification

OH bend, vt = 0 OH bend, vt = 1In-plane rock, vt = 1-0 U0 subband

1100.0

1200.0

1300.0

1400.0

1500.0

1600.0

1700.0

1800.0

0 1 2 3 4 5 6 7 8 9 10 11 12

K-Reduced Torsion-Vibration Energy Map

K Value

K-R

educ

ed E

nerg

y (c

m-1)

Connect the Dots???

1100.0

1200.0

1300.0

1400.0

1500.0

1600.0

1700.0

1800.0

0 1 2 3 4 5 6 7 8 9 10K Value

K-R

educ

ed E

nerg

y (c

m-1)

O-18 K-Reduced Torsion-Vibration Energy Map (sensitive to K = 0 anharmonic perturbations)

CO stretch, vt = 0

CO stretch, vt = 1

CO stretch, vt = 2

In-plane rock, vt = 0

In-plane rock, vt = 1

Out-of-plane rock, vt = 0

U0 substates

CH3 asym bend, vt = 0

OH bend, vt = 0

OH bend, vt = 1U1 substates

U2 substates

1400

1405

1410

1415

1420

1425

1430

0 5 10 15 20 25 30 35 40

( A,co,0,9)

( A,co,1,5)

( A,ri,1,1+)

( A,ri,1,1-)

( A,co,1,0)

( A,ri,0,8)

( A,co,1,3)

( A,ro,0,6)

Level-Crossing Resonances

J Value

J-R

educ

ed E

nerg

y (c

m-1)

CH3 o-o-p rock

CH3 in-plane rock

CO stretch

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).

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, CH3

18OH 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.