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Is the Equilibrium Structure of BeOH Linear or Bent? Kyle Mascaritolo Dr. Michael Heaven

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Significance of Research Monohydroxides of Mg, Ca, Sr and Ba have all been studied experimentally and computationally For the Ground State: Linear: CaOH, SrOH, BaOH [1-3] – Ionic Bonding M + X - Quasilinear: MgOH [4] – Some Covalency, barrier to linearity < 2 cm -1 BeOH calculated to be bent, but little experimental data 1.D.O. Harris, J. Mol. Spectrosc. 97, 73 1983. 2.D.O. Harris, J. Mol. Spectrosc. 97, 37 1983. 3.P.F. Bernath, J. Chem. Phys. 84, 698 1986. 4.Y. Ni, Ph.D. thesis, Uni. California, Santa Barbara, 1986.

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Past Computational Findings Several high-level ab initio calculations for BeOH predict: [1-3] – Equilibrium ∠ BeOH ranging 134° - 152° – Barrier to linearity up to 136 cm -1, but as low as 50 cm -1 – Near Prolate Top: B 0 ≈ 1.29 cm -1 – A significant contribution of covalency to the Be-O bonding 1.Theodorakopoulos, Petsalakis, and Hamilton J. Chem. Phys. 111, 23 1999. 2.Koput and Peterson J. Phys. Chem. A 107, 2003. 3.Palke and Kirtman Chem. Phys. Lett. 117, 5 1985.

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Barrier to Linearity: 136 cm -1 ∠ BeOH = 140.9° Possibly quasilinear in ground state Method: RCCSD(T) cc-pV5Z Equilibrium Bending Potential with v l 2 Bending Energy Levels Koput and Peterson J. Phys. Chem. A 107, 2003.

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CASSCF/MRCI/ aug-cc-pVTZ 1 2 A” State Calculations R(BeO)=1.457, R(OH)=0.954, = 127.6; B 0 =1.228 cm -1 Calculations done by Dr. Michael Heaven Excited states shifted down for comparison Renner-Teller

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Past Experimental Results Low resolution gas phase electronic spectroscopy – 300 – 330nm (30300 – 33330 cm -1 ) – Was not analyzed in detail A. Antic-Jovanovic, V. Bojovic, D. Pesic, Spectrosc. Lett. 21, 8 1988.

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Experimental Setup: Laser Induced Fluorescence and 1 + 1’ Resonance Enhanced Multiphoton Ionization Spectroscopies LIF and REMPI Excitation Photon: Doubled output of 2 nd Harmonic Nd:YAG pumped dye laser (Quanta Ray PDL1) REMPI Ionization Photon: 248nm from KrF Excimer (COMPexPro 102) Ablation Photon: Fundamental of Nd:YAG (Continuum Mini-Lite II) Base Pressure: 1x10 -7 Torr Base Pressure: 1x10 -9 Torr Smalley Laser Ablation

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1 + 1’ REMPI Survey BeOH BeOD 752 cm -1 708 cm -1 579 cm -1 561 cm -1 517 cm -1 00 0 0 Transitions from 00 0 0 02 0 0 ? 01 1 0 00 0 0 01 1 0 03 1 0 02 0 0

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Negative Anharmonicity of MgOH/OD Y. Ni, Ph.D. thesis, Uni. California, Santa Barbara, 1986.

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Laser Induced Fluorescence

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LIF of Current Lowest Rovibronic Transition K’=0 ← K”=1 K’=2 ← K”=1 K’=1 ← K”=0 K’=0 ← K”=1 BeOH Perpendicular transitions

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Energy Level Diagram for Prolate Top ∆K = ±1 ∆J = 0,±1 E = BJ(J+1)+(A-B)K 2 J=0 1 2 3 1 2 3 1 2 3 1 2 3 2 3 2 3 K=0K=1K=2 v” v' ≈160 cm -1 BeOH ≈100 cm -1 BeOD T = 15K kT ≈ 11 cm -1 ≈40 cm -1 BeOH ≈26 cm -1 BeOD

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BeOD Obs. Calc. BeOH K’=0 ← K”=1K’=1 ← K”=0K’=2 ← K”=1

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BeOD Obs. Calc. BeOH K’=0 ← K”=1K’=1 ← K”=0K’=2 ← K”=1

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K’ = 2 ← K”=1? Q R(0) R(1) R(2) P(1) P(2)P(3) P(4) R(1) R(2) P(3)P(4) Q Be 2 O?

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BeOD Obs. Calc. BeOH K’=0 ← K”=1K’=1 ← K”=0K’=2 ← K”=1

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LIF of Current Lowest Rovibronic Transition K’=0 ← K”=1 K’=2 ← K”=1 K’=1 ← K”=0 K’=0 ← K”=1 BeOH

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BeOD K’=1 ← K”=0 K’=0 ← K”=1 Simulation done with PGOPHER

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1 + 1’ REMPI Survey BeOH BeOD If we have K’=0 ← K”=1, then why no K’=2 ← K”=1?

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BeOH BeOD Constants 00 0 01.246(14)1.2453(86) 01 1 01.2485(84)1.2461(88) 00 0 01.280(15)1.224(13) 00 0 01.1892(86)1.1860(63) 01 1 01.134(11)1.1333(96) 02 0 01.0934(80)1.0922(87) 03 1 01.106(27)1.100(21)

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So is it bent? We think so.

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Future Work Explore to higher and lower energy Make spectra “hot” by increasing ablation laser power to populate K” = 1,2,… PFI-ZEKE to get geometry of cation Find ionization potential

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Acknowledgements Labmates Ivan Antonov Keith Freel Joshua Bartlett Michelle Sullivan Jiande Han Past Work Jeremy Merritt

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Thank you.

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Quasilinear MgOH/OD r x /r e = 1.38 for MgOH stated by Murad r x > 2r e to be ionic (r x = 2.5 Å, r e = 1.8 Å) rxrx E. Murad, J. Chem. Phys. 75 1983.

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Ground State Bending Potential of BeOH at Different R Be-O Bond Lengths R Be-O ≤ 2.4 Bohr → Linear R Be-O ≥ 2.4 Bohr → Bent Calculated Equilibrium: R Be-O = 2.6 Bohr (1.3775 Å) at ∠ BeOH = 142.5° Barrier to Linearity = 50 cm -1 Method: MRD-CI Theodorakopoulos, Petsalakis, and Hamilton J. Chem. Phys. 111, 23 1999.

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Past Experimental Results Ar Matrix-isolated ESR spectroscopy [1] – Assumed ionic – Small evidence of bent structure taken as false signal Low resolution gas phase electronic spectroscopy [2] – 300 – 330nm (30300 – 33330 cm -1 ) – Was not analyzed in detail 1.J.M. Brom, Jr. and W. Weltner, Jr. J. Chem. Phys. 64, 9 1976. 2.A. Antic-Jovanovic, V. Bojovic, D. Pesic, Spectrosc. Lett. 21, 8 1988.

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LIF of 2 A”- X 2 A’: Be 16 OH & Be 18 OH Simulation with B’=1.22, B”=1.28 cm -1 T=20 K obs. calc. Effects of Isotopic Substitution Work done by Jeremy Merritt: M. Heaven Doesn’t show asymmetric splittings. Deuteration needed to characterize bending motion.

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BeOD

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Laser Induced Fluorescence

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BeOD 00 0 0 01 1 0 v 2 predicted at 52.9 cm -1 Koput and Peterson J. Phys. Chem. A 107, 2003.

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BeOH BeOD K’=1 ← K”=0 K’=0 ← K”=1 Simulation done with PGOPHER ∠ BeOH” = 167.8° ∠ BeOH’ = 158.6°

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BeOD Obs. Calc. BeOH K’=0 ← K”=1K’=1 ← K”=0K’=2 ← K”=1 ∠ BeOH” = 141.2° ∠ BeOH” = 158.7°

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BeOH BeOD Constants A”A’ 00 0 085.630(50)1.246(14)40.168(85)1.2453(86) 01 1 082.3764(28)1.2485(84)47.610(68)1.2461(88) 00 0 073.289(23)1.280(15)59.069(89)1.224(13) A”A’ 00 0 026.85(50)1.1892(86)46.399(53)1.1860(63) 01 1 026.978(71)1.134(11)47.353(70)1.1333(96) 02 0 026.8146(45)1.0934(80)49.736(48)1.0922(87) 03 1 021.21(14)1.106(27)58.90(13)1.100(21)

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