CALIFORNIA INSTITUTE OF TECHNOLOGY PURE ROTATIONAL SPECTROSCOPY OF PANHs: 1,10-PHENANTHROLINE Brett A. McGuire, Ian A. Finneran, P. Brandon Carroll, & Geoffrey A. Blake

INTRODUCTION Why PA(N)Hs?

INTRODUCTION Why PA(N)Hs? - Prolific in the ISM

INTRODUCTION Why PA(N)Hs? - Only two definitively identified (C 60 & C 70 ) - Prolific in the ISM

INTRODUCTION Why PA(N)Hs? - Fascinating dynamical systems - Prolific in the ISM - Only two definitively identified (C 60 & C 70 )

INTRODUCTION Why PA(N)Hs? - Testbeds for FIR large amplitude motion studies - Prolific in the ISM - Only two definitively identified (C 60 & C 70 ) - Fascinating dynamical systems

INTRODUCTION Why PA(N)Hs? - Prolific in the ISM - Only two definitively identified (C 60 & C 70 ) - Fascinating dynamical systems - Testbeds for FIR large amplitude motion studies 1,10-phenanthrolineAcridinePhenanthridine

INTRODUCTION Why (These) PANHs? 1,10-phenanthrolineAcridinePhenanthridine - Large dipole moments - Comparatively small and simple - Rigid structure simplifies spectral analysis - Previous rotational studies below 85 GHz

INTRODUCTION - ASTROCHEMISTRY PA(N)Hs are ubiquitous in the ISM

INTRODUCTION - ASTROCHEMISTRY PA(N)Hs are ubiquitous in the ISM Aromatic Skeleton C2H2C2H2 C2H2C2H2 C2H2C2H2 C2H2C2H2 PAHs

INTRODUCTION - ASTROCHEMISTRY PA(N)Hs are ubiquitous in the ISM Aromatic Skeleton C2H2C2H2 C2H2C2H2 C2H2C2H2 C2H2C2H2 PAHs Aromatic Skeleton C2H2C2H2 HCNC2H2C2H2 PANHs

INTRODUCTION - ASTROCHEMISTRY PA(N)Hs are ubiquitous in the ISM Aromatic Skeleton C2H2C2H2 C2H2C2H2 C2H2C2H2 C2H2C2H2 PAHs Aromatic Skeleton C2H2C2H2 HCNC2H2C2H2 PANHs Size distribution, charge, and C/N fraction dependent on: - Local N budget - UV Radiation Flux - Temperature - Density

INTRODUCTION - ASTROCHEMISTRY PA(N)H spectra are ambiguous Figure from Peeters 2011, Proc. IAU Sym 280, adapted from Cami et al. 2011, EAS Pubs,46, 117 Simulated Observed Residual Can reproduce observed PA(N)H features with astonishingly good fits using the entire NASA Ames PAH Spectral Database 6.2 µm 7.7 µm 11.0 µm 11.2 µm PANHs Size Distr. Neutral PAHs PAH Cations Lack any molecular specificity

INTRODUCTION - ASTROCHEMISTRY PA(N)H spectra are ambiguous Simulated Observed Residual Can reproduce observed PA(N)H features with astonishingly good fits using the entire NASA Ames PAH Spectral Database 6.2 µm 7.7 µm 11.0 µm 11.2 µm PANHs Size Distr. Neutral PAHs PAH Cations Lack any molecular specificity Need 1) Foundational observations for targeted searches with ALMA 2) Laboratory rotational spectra Figure from Peeters 2011, Proc. IAU Sym 280, adapted from Cami et al. 2011, EAS Pubs,46, 117

INTRODUCTION - PROPOSED OBSERVATIONS NGC – 18 μm emission in target region - associated with neutral poly-aromatics 6 m primary beam~ 120” 10 m primary beam~ 75” Mosaic coverage~ 75” Synthesized beam~ 5” x 4” Figures adapted from Peeters et al. 2012, ApJ, 747, 44. CARMA Array (Owens Valley, CA) Targeting HCN, HCO +, & CO In: NGC Reflection Nebula (RN) L134 N - Cold, Dark Molecular Cloud GGD 27 - ILL - Illuminating Source for a RN IRAC [8.0] Surface Brightness

AB INITIO CALCULATIONS – NEUTRAL PANHS Laboratory studies of larger and larger PA(N)Hs will become impractical in the mm and submm Low temperature mw studies will help, but will need excellent theory

Laboratory studies of larger and larger PA(N)Hs will become impractical in the mm and submm Low temperature mw studies will help, but will need excellent theory Previous studies 1 show good agreement with experiment for: Structures, Rotational Constants: B3LYP/cc-pVTZ Distortion Constants:B3LYP/ G** SCF/DZP (w/ ACESII) Are there better methods? 1 McNaughton et al. 2008, ApJ, 678, 309 AB INITIO CALCULATIONS – NEUTRAL PANHS

2 Steber 2011, 66th Mol Spec Conference 1 Zhao 2008, Theor Chem Account, 120, 215 M06-2X? - DFT method - improvement on B3LYP 1 - Optimized to better handle long-range interactions on main group atoms - Shown to have an excellent cost-benefit ratio for structures and energies (specifically of clusters and larger species) 2 AB INITIO CALCULATIONS – NEUTRAL PANHS

McNaughton et al. 2008, ApJ, 678, 309 Acridine Constant B3LYP/ G** MP2/ G** M062X/ 6-31G M062X/ 6-31+G** M062X/ G** Rotational0.14(0.10)0.51(0.06)0.31(0.10)0.18(0.08)0.50(0.07) Distortion3.99(2.87)5.47(6.61)4.60(2.87)3.99(2.58) Phenanthroline Constant B3LYP/ G** MP2/ G** M062X/ 6-31G M062X/ 6-31+G** M062X/ G** Rotational0.24(0.09)0.49(0.04)0.37(0.29)0.17(0.07)0.50(0.10) Distortion15.64(24.78)8.63(2.90)10.49(11.08)49.01(84.25) Phenanthridine Constant B3LYP/ G** (SCF/DZP) MP2/ G** M062X/ 6-31G M062X/ 6-31+G** M062X/ G** Rotational0.16(0.13)0.49(0.01)0.16(0.11)0.18(0.16)0.48(0.15) Distortion11.82(0.58)7.54(0.40)2.67(0.44)5.06(1.17) x 100% Exp Exp - Calc AB INITIO CALCULATIONS – NEUTRAL PANHS

McNaughton et al. 2008, ApJ, 678, 309 Conclusion? M062X/6-31+G** - Same or better accuracy on A, B, C - Extremely fast - Same or better accuracy on distortion constants without resorting to additional calculations x 100% Exp Exp - Calc AB INITIO CALCULATIONS – NEUTRAL PANHS Acridine Constant B3LYP/ G** MP2/ G** M062X/ 6-31G M062X/ 6-31+G** M062X/ G** Rotational0.14(0.10)0.51(0.06)0.31(0.10)0.18(0.08)0.50(0.07) Distortion3.99(2.87)5.47(6.61)4.60(2.87)3.99(2.58) Phenanthroline Constant B3LYP/ G** MP2/ G** M062X/ 6-31G M062X/ 6-31+G** M062X/ G** Rotational0.24(0.09)0.49(0.04)0.37(0.29)0.17(0.07)0.50(0.10) Distortion15.64(24.78)8.63(2.90)10.49(11.08)49.01(84.25) Phenanthridine Constant B3LYP/ G** (SCF/DZP) MP2/ G** M062X/ 6-31G M062X/ 6-31+G** M062X/ G** Rotational0.16(0.13)0.49(0.01)0.16(0.11)0.18(0.16)0.48(0.15) Distortion11.82(0.58)7.54(0.40)2.67(0.44)5.06(1.17)

SPECTROSCOPY - EXPERIMENTAL APPROACHES Spectra of these molecules at higher frequencies is essential for accurate evaluation of distortion constants

BACKGROUND - PROTONATED PANHS Protonated PANHs

BACKGROUND - PROTONATED PANHS Protonated PANHs - Fundamentally interesting for spectroscopic and dynamical studies (protonation dynamics, proton roaming...) - Known to be a major constituent of observed PA(N)H emission

THEORY - PROTONATED PHENANTHROLINE 0 kcal/mol Energy M062X/ G**

THEORY - PROTONATED PHENANTHROLINE kcal/mol kcal/mol kcal/mol 0 kcal/mol Energy kcal/mol kcal/mol M062X/ G**

THEORY - PROTONATED PHENANTHROLINE kcal/mol kcal/mol Energy kcal/mol kcal/mol kcal/mol kcal/mol kcal/mol kcal/mol M062X/ G** 0 kcal/mol

THEORY - PROTONATED PHENANTHROLINE kcal/mol Energy kcal/mol kcal/mol kcal/mol kcal/mol kcal/mol kcal/mol M062X/ G** kcal/mol T.S. 0 kcal/mol

Still require spectra of neutral precursors... THEORY - PROTONATED PHENANTHROLINE

BACKGROUND - PANH-WATER CLUSTERS PANH - Water Clusters

BACKGROUND - PANH-WATER CLUSTERS - Spectroscopically interesting - Potentially relevant to grain - water interactions in interstellar dusts and ices - Applications to coherent control of large amplitude motions PANH - Water Clusters

COMPUTATIONAL STUDIES - PANH-WATER MP G** M06-2X G** A (MHz) B (MHz) C (MHz) ΔJ (KHz)0.003 ΔK (KHz) ΔJK (KHz)0.518 H 2 O in-plane wag (cm -1 )2132 H 2 O stretch (cm -1 )3439 N-H Bond (Å) C-N-O Angle (°) Binding Energy (kcal/mol) Lit = 7.6 Mitsui et al. 2000, Chem Phys Lett, 317, 211 For more on THz coherent control: Doslic 2006, J. Phys. Chem. A., 110, Theoretical Jewriya et al. 2010, PRL, 105, Experimental

COMPUTATIONAL STUDIES - PANH-WATER Phenanthridine M06-2X G** A (MHz) B (MHz) C (MHz) N-H Bond (Å)1.954 Binding Energy (kcal/mol) 7.7 Phenanthroline M06-2X G** A (MHz) B (MHz) C (MHz) N-H Bond (Å)2.158 Binding Energy (kcal/mol) 9.6

COMPUTATIONAL STUDIES - PANH-WATER Still require spectra of monomeric precursors...

SPECTROSCOPY - EXPERIMENTAL APPROACHES mTorr / °C H 2 O outH 2 O in Sample To Vac GHz To Computer H 2 O outH 2 O in Ar in To Vac GHz To Computer Ar + Sample 100 °C

SPECTROSCOPY - EXPERIMENTAL APPROACHES mTorr / °C H 2 O outH 2 O in Sample To Vac GHz To Computer H 2 O outH 2 O in Ar in To Vac GHz To Computer Ar + Sample 100 °C Cold

SPECTROSCOPY - EXPERIMENTAL APPROACHES Rooftop Reflector 1 mm Pinhole Copper Sheath Cartridge Heaters Ar In Wire Mesh Solid Sample

SPECTROSCOPY - EXPERIMENTAL APPROACHES GHz H 2 O outH 2 O in To Vac Still Cold 100 °C To Computer Wire Grid Polarizer Ar + Sample Still Cold Configured for both continuous flow and pulsed operation

SPECTROSCOPY - EXPERIMENTAL APPROACHES GHz To Computer To Vac Sample mTorr / 25 °C GHz To Computer To Vac Sample mTorr / 40 °C

SPECTROSCOPY - PRELIMINARY DATA M

M

M

M

No match in any database to any molecule previously run in this cell, nor to any collected spectra A promising start, but impossible to determine w/o low frequency data