Pure Rotational and UltravioletMicrowave Double Resonance Spectroscopy of

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Pure Rotational and Ultraviolet-Microwave Double Resonance Spectroscopy of Two Water Complexes of para-methoxyphenylethylamine (p.

Pure Rotational and Ultraviolet-Microwave Double Resonance Spectroscopy of Two Water Complexes of para-methoxyphenylethylamine (p. MPEA) Justin L. Neill, Matt T. Muckle and Brooks H. Pate, Department of Chemistry, University of Virginia Ryan G. Bird, David W. Pratt, Department of Chemistry, University of Pittsburgh

Spectroscopy of p. MPEA and p. MPEA-water Unamuno et al. p. MPEA Seven conformers

Spectroscopy of p. MPEA and p. MPEA-water Unamuno et al. p. MPEA Seven conformers reported: Martinez et al, J. Mol. Spectrosc. 158 (1993) 82 -92. Complete (correct) structural assignment: Robertson, Simons, and Mons, J. Phys. Chem. A 105 (2001) 9990. Yi, Robertson, and Pratt, Phys. Chem. Phys. 4 (2002) 5244 -5248. (rotationally resolved LIF) Douglass et al. , MF 02, ISMS (2006) (CP-FTMW and UV-MW) Cortijo, Alonso, and López, Chem. Phys. Lett. 466 (2008) 214 -218. (MW) Unamuno et al. p. MPEA-water Two clusters found, binding energies measured, assigned to structures: Unamuno et al, Chem. Phys. 271 (2001) 55 -69.

Conformational Landscape of p. MPEA B AA C C B F F G G

Conformational Landscape of p. MPEA B AA C C B F F G G DD EE Conformer E (cm-1) E-8 0 D-5 34 C-7 38 A-4 54 B-1 351 F-2 489 G-3 498 6 675 9 678 mp 2/6 -31 g** Yi, Robertson, and Pratt, Phys. Chem. Phys. 4 (2002) 5244 -5248.

New CP-FTMW Measurements Sample acquired from Aldrich (98%); placed in reservoir within nozzle, heated

New CP-FTMW Measurements Sample acquired from Aldrich (98%); placed in reservoir within nozzle, heated to approximately 100°C, seeded in He/Ne supersonic expansion. (No water added) CP-FTMW sample reduction techniques: 3 nozzles 10 FIDs per valve pulse Collected 995, 000 FIDs, using 298, 500 valve pulses, equivalent sensitivity to 8. 955 million pulses with a single nozzle! Measurement time: 48 hours (consecutive) G. G. Brown, B. C. Dian, K. O. Douglass, S. M. Geyer, S. T. Shipman, and B. H. Pate, Rev. Sci. Instrum. 79 (2008) 53103 -1 -13.

New CP-FTMW Measurements 3 nozzles, 995, 000 FIDs (298, 500 pulses) versus 1 nozzle,

New CP-FTMW Measurements 3 nozzles, 995, 000 FIDs (298, 500 pulses) versus 1 nozzle, 80, 000 FIDs (80, 000 pulses) Scaled to match signal heights on strongest transitions

New CP-FTMW Measurements 3 nozzles, 995, 000 FIDs (298, 500 pulses) versus 1 nozzle,

New CP-FTMW Measurements 3 nozzles, 995, 000 FIDs (298, 500 pulses) versus 1 nozzle, 80, 000 FIDs (80, 000 pulses) Scaled to match signal heights on strongest transitions 2008 spectrum much richer than 2006…(used same bottle)

New Transitions Several unassigned Q-branches observed. For near-prolate top, b/c-type Q-branches are located at

New Transitions Several unassigned Q-branches observed. For near-prolate top, b/c-type Q-branches are located at approximately (A-(B+C)/2)*(2 K-1), so the ratio between two Q-branches gives you their K assignments and A-(B+C)/2. Pattern of the Q-branches gives (B-C), then (A+B+C) can be varied until the strong b/c-type R-branches are fit. Two new spectra were assigned this way.

New Transitions

New Transitions

p. MPEA-water Fit Parameters Conformer D-water A/MHz B/MHz C/MHz χaa/MHz χbb-χcc/MHz Nlines rms error/k.

p. MPEA-water Fit Parameters Conformer D-water A/MHz B/MHz C/MHz χaa/MHz χbb-χcc/MHz Nlines rms error/k. Hz µa/D µb/D µc/D Experiment 1740. 6781(7) 430. 5044(4) 380. 0915(4) 0. 20(6) -2. 419(26) 224 24. 2 b≈c Theory 1769. 85 426. 01 376. 65 0. 41 -2. 19 0. 64 2. 84 2. 60 Conformer E-water A/MHz B/MHz C/MHz χaa/MHz χbb-χcc/MHz Nlines rms error/k. Hz µa/D µb/D µc/D Experiment 1533. 8873(10) 457. 8598(5) 398. 9191(9) 0. 785(47) -2. 31(44) 137 12. 7 c only Theory 1552. 23 452. 47 383. 61 0. 97 -2. 04 0. 47 0. 49 2. 32 Ab initio: b 3 pw 91/6 -311+g(df, pd), using effective Q and recommended basis set of W. C. Bailey (http: //homepage. mac. com/wcbailey/nqcc/) All fits performed using SPFIT (Pickett), with standard errors determined by PIFORM (Kisiel). (Quartic distortion parameters not listed) Observed structures are analogous to those of other similar structures: tryptamine (Felker, J. Phys. Chem. 96 (1992) 7844); 2 -phenylethylamine (Melandri, et al, RC 13)

Coherence-Converted Population Transfer UV-FTMW Spectroscopy Continuum MW Synthesizer 2 GS/s AFG Nd: YAG ν

Coherence-Converted Population Transfer UV-FTMW Spectroscopy Continuum MW Synthesizer 2 GS/s AFG Nd: YAG ν 0 10 Hz rep. rate v 0 + 30 MHz 200 m. J/p 532 nm Pulsed 1 watt amp Single Sideband ν 0 Dye laser Lambda Physik 0. 025 cm-1 5 m. J/p UV All spectra are ~0. 1 cm-1 blue-shifted due to coaxial arrangement. bandwidth Rhodamine 6 G dye, doubled with BBO SHG crystal 1 Gs/s Oscilloscope (30 MHz Carrier) Free Induction Decay T. J. Balle and W. H. Flygare, Rev. Sci. Instrum. 52, 33 (1981) M. Nakajima, Y. Sumiyoshi, and Y. Endo, Rev. Sci. Instrum. 73, 165 (2002) R. D. Suenram, J. U. Grabow, A. Zuban, and I. Leonov, Rev. Sci. Instrum. 70, 2127 (1999) Douglass, Johns, Nair, Brown, Rees, and Pate, J. Mol. Spectrosc. 239, 29 (2006)

p. MPEA-water UV-FTMW Flowed He/Ne gas over cooled (0°C) water reservoir before entering chamber;

p. MPEA-water UV-FTMW Flowed He/Ne gas over cooled (0°C) water reservoir before entering chamber; increased signals by around a factor of 5 (as strong as monomer) With the water reservoir at room temperature, signal started to drop again (higher water clusters? )

Ab Initio Relative Energies (cm-1) Conformer A-4 B-1 C-7 D-5 E-8 F-2 G-3 6

Ab Initio Relative Energies (cm-1) Conformer A-4 B-1 C-7 D-5 E-8 F-2 G-3 6 9 Monomer 54 351 38 34 0 489 498 675 678 1023 1427 1005 44 0 918 946 1210 816 Water cluster mp 2/6 -31 g** p. MPEA(E)-water p. MPEA(C)-water p. MPEA(9)-water

p. MPEA-water UV-FTMW The assignments of Unamuno et al are correct— 35670 cm-1 feature

p. MPEA-water UV-FTMW The assignments of Unamuno et al are correct— 35670 cm-1 feature is due to water with conformer 5; 35681 cm-1 feature is due to water with conformer 8. Their assignments were based on structural stability—conformer 8+water goes to strongest peak, conformer 5+water to second-strongest—and low-frequency vibrational mode calculations.

Residual Spectrum Strongest p. MPEA transition intensity 120 µV No residual transitions with resolved

Residual Spectrum Strongest p. MPEA transition intensity 120 µV No residual transitions with resolved quadrupole hyperfine splitting—not p. MPEA, or simply a function of cluster size? (large number of hyperfine-resolved transitions for assigned p. MPEA-H 2 O clusters) Possibilities: Other conformers with water; water molecule on the methoxy group? (Unlikely due to energetics) Two waters or more? (more likely—ab initio calculations needed) Remeasure CP-FTMW spectrum with water added! MW-MW double resonance spectroscopy needed

Acknowledgements Funding: NSF CRIF: ID (CHE-0618755) Jefferson Scholars Foundation (J. Neill) Tektronix

Acknowledgements Funding: NSF CRIF: ID (CHE-0618755) Jefferson Scholars Foundation (J. Neill) Tektronix

p. MPEA-water Fit Parameters Conformer D-water A/MHz B/MHz C/MHz DJ/k. Hz DJK/k. Hz DK/k.

p. MPEA-water Fit Parameters Conformer D-water A/MHz B/MHz C/MHz DJ/k. Hz DJK/k. Hz DK/k. Hz d. J/k. Hz d. K/k. Hz χaa/MHz χbb-χcc/MHz Nlines rms error/k. Hz µa/D µb/D µc/D Experiment 1740. 6781(7) 430. 5044(4) 380. 0915(4) 0. 0496(13) -0. 223(6) 2. 586(13) 0. 0114(5) 0. 32(5) 0. 20(6) -2. 419(26) 224 24. 2 b≈c Theory 1769. 85 426. 01 376. 65 0. 41 -2. 19 0. 64 2. 84 2. 60 Conformer E-water A/MHz B/MHz C/MHz DJ/k. Hz DJK/k. Hz DK/k. Hz d. J/k. Hz d. K/k. Hz χaa/MHz χbb-χcc/MHz Nlines rms error/k. Hz µa/D µb/D µc/D Experiment 1533. 8873(10) 457. 8598(5) 398. 9191(9) 0. 0573(35) -0. 063(12) 1. 468(34) 0. 0113(20) 0. 23(8) 0. 785(47) -2. 31(44) 137 12. 7 c only Theory 1552. 23 452. 47 383. 61 0. 97 -2. 04 0. 47 0. 49 2. 32 Observed structures are analogous to those of other similar structures: tryptamine (Felker, J. Phys. Chem. 96 (1992) 7844); 2 -phenylethylamine (Melandri, et al, RC 13)