Rotationally-Resolved Spectra of 2-methylfuran from the cm-wave to the far IR Steven T. Shipman, Ian A. Finneran, Susanna L. Widicus Weaver, and Jennifer van Wijngaarden

2-methylfuran W. G. Norris and L. C. Krisher, J. Chem. Phys. 51, (1969). U. Andresen and H. Dreizler, Z. Naturforschung 25a, 570 (1970). Small, volatile organic compound Methyl rotor complicates spectrum First assignments by Norris and Krisher (1969) Andresen and Dreizler measured dipole (1970)  a = 0.31 D,  b = 0.57 D,  c = 0 D (planar) V 3 = cm -1 Mid-to-high K a : level mixing c-types borrow intensity from b-types

Forbidden c-types Forbidden c-types are > 80% of E-state peaks from 8.7 – 18.3 GHz at 273 K

1)Chirped-pulse generated by AWG, mixed with PLDRO. 2) Sideband is amplified and sent into sample cell. (10 mTorr, 0 °C typical) 3)Molecular FID is amplified and mixed with PLDRO. 4)Downconverted FID is detected with oscilloscope. Chirped-Pulse Spectrometer New this year Amps and multipliers for 18 – 26.5 GHz. Working on DR across full range.

Spectra from 8 – 26.5 GHz A-E splitting GS: 3.2 MHz v = 1: MHz M shots 3091 peaks above 3:1 Tallest peaks are b Q Remainder are b R, b P, c R, c P M shots 740 peaks above 3:1

1 – 50 GHz Frequency Synthesizer VDI Multiplier chain 50 GHz – 1.2 THz Detector Gas Flow Cell To Computer Sample InputTo Vacuum Pump Carroll, Drouin, & Widicus Weaver ApJ 723, 2010 Source modulated at 15 kHz HEB signal detected with lock-in at 2f 100 kHz point spacing, 2.5 GHz / hour. Direct Absorption Flow Cell

2-mf mm- and submm-wave data mainly a R, b R weak b Q b R, c R Conservative estimate: 45,806 peaks from 75 – 960 GHz 11,509 assigned to GS 2,580 assigned to v tors = 1 Assigned ~31% of the features (Q vib at 298 K is ~ 5)

Fitting Strategies / Challenges Needed “unusual” tunneling parameters in ERHAM: GS uses an S-reduction parameter Both use parameters for sextic distortion constants fixed to 0. Initial fitting done with recompiled XIAM Fine for cm-wave data, but problems near K a = 11 with high frequency data Switching to ERHAM resolved this Extensive use of combination loops in assignment of weak b Q transitions GSv = 1 Fit RMSParametersFit RMSParameters XIAM263 kHz18> 16 MHz18 ERHAM108 kHz19113 kHz23

Far IR Spectroscopy at the CLS Bruker IFS 125HR cm -1 resolution (28.75 MHz) 2 m multipass cell – 36 passes Data collected at 298 K Located in Saskatoon, SK Beam at 2.9 GeV Most beamlines are X-ray, but two for IR: Far IR (5 – 1000 cm -1 ) Mid IR (560 – 6000 cm -1 )

2-mf Vibrational Modes cm -1, 6.6 out-of-plane bend cm -1, 2.4 in-plane bend cm -1, 7.2 ring puckering mode cm -1, 1.3 ring puckering mode B3LYP / G(d,p), with anharmonic frequency corrections Si detector Ge/Cu detector Low pressure High pressure

50 – 400 cm -1 : 130 mTorr, 88 IFGs 960 mTorr, 314 IFGs 500 – 1100 cm -1 : 125 mTorr, 103 IFGs 525 mTorr, 309 IFGs Roughly 5 IFGs / hour CLS Data Overview 29 c-type 20 b-type 28 c-type 27 c-type 960 mTorr 525 mTorr

CLS Data – Expanded Views Hot bands! Multiple Q-branches (oop bend) R-branch (ip bend) 130 mTorr 960 mTorr 130 mTorr P-branch (oop bend) 960 mTorr

Summary and Future Work Beam time from August 8 – 13. Use chilled cell to reduce number of hot bands. Fit far IR data, use constants as starting point for U-lines in 8.7 – 960 GHz data. Use full data set as testbed for developing more automated fitting routines. Future work: Comprehensive fit of 2-methylfuran ground and first excited states. Fitting with ERHAM was more successful than with XIAM; some strangeness with tunneling parameters, though. Room-temperature data collected from 50 – 400 cm -1 and 500 – 1100 cm -1. Analysis greatly complicated by hot bands.

Acknowledgments Funding Dr. Brant Billinghurst Canadian Light Source van Wijngaarden group University of Manitoba Widicus Weaver group Emory University Shipman group New College of Florida Noah Anderson (2012) Brittany Gordon (2013) Erin Kent (2013) Sophie Lang (2014) Morgan McCabe (2014) Sam McCamant (2013) Christian Metzger (2013) Maria Phillips (2013) Ben Rooks (2013) Suzanne Setti (2014)

κ ~ for 2-methylfuran Adapted from Gordy and Cook, fig and 12.8 Example: R-Branch, v t =1

2-mf features (simulated) a R and b R dominant Sparse b R and c R Weaker b Q (offset) b R and c R dominant Very weak b Q (offset)

Ground State Fit Table (Partial) GSCalculatedERHAMXIAM A (MHz) (12) (33) B (MHz) (46) (20) C (MHz) (36) (38) D J (kHz) (58) (68) D JK (kHz) (66) (31) D K (kHz) (83) (31) d J (kHz) (24) (32) d K (kHz) (86) (17) V 3 (cm -1 ) (74) < (i,a) (32) 3.30(13) < (i,b) (32)86.70(13) < (i,c)90.00 [90.00]90.009(18) J max K a max 5453 N  fit (MHz) ww ERHAM distortion constants much closer to ab initio (MP2/ G(d,p)) than XIAM. N is distinct frequencies (blends only counted once); 19,143 GS transitions in fit.

Rest of the fit tables v = 1 (ERHAM) A (MHz) (18) B (MHz) (22) C (MHz) (65)  J (kHz) (50)  JK (kHz)1.8300(31)  K (kHz)-1.947(21)  J (kHz) (24)  K (kHz)0.6824(14)  JK (mHz)-2.852(63)  K (mHz)-7.01(64) v = 1 (cont’d)  1 (MHz) (72) B020 1 (MHz) (35) B200 1 (MHz) (49) B220 1 (kHz) (27) B022 1 (kHz) (14) B202 1 (Hz)-5.335(12) B040 1 (kHz)0.806(10) B400 1 (kHz) (23) B240 1 (Hz)0.0785(35) B042 1 (Hz)0.0523(25) B420 1 (mHz)1.354(61) GSXIAM ERHAM  JK (mHz) (45) (83)  KJ (mHz) 0.568(50)[0.0]  K (mHz) [0.0]1.882(20)  JK (mHz) (29)[0.0]  (44) (14)  Jm (MHz) (30) B020 1 e (kHz) 1.051(29)  Km (MHz) (73) B220 1 (Hz) (88)  m (MHz) (27) B202 1 (Hz) (11) B004 1 (Hz) (84) B600 1 (mHz) (23)  1 (MHz) (11) v = 1 (cont’d)  (90)  (degrees)2.1785(31) J max114 K a max15 N2580 b  fit (MHz)0.113 wawa 0.753

Other Excited States? W. G. Norris and L. C. Krisher, J. Chem. Phys. 51, (1969). Assigned just over 30% of the peaks to GS and v=1 of methyl torsion. Q vib at 298 K is ~ 5. Norris and Krisher: 14 peaks from 20 – 30 GHz assigned to v=1 of ring-puckering mode. Probably out-of-plane / in-plane bend instead (237 / 339 vs 603 cm -1 ) We observe 9 of these, but only 6 have correct intensities. Can’t extend fits using N&K constants. Plan: Get constants from CLS for excited states and go back to 8.7 – 960 GHz data.