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Spectroscopic Research of Pt + NH 3

Spectroscopic Research of Pt + NH 3. The Search for Polyatomic Molecules. 13450. 13200. Jamie Gengler , Timothy Steimle, and Jinhai Chen Dept. of Chemistry & Biochemistry Arizona State University, Tempe, AZ 85287 June 21, 2005. Funded by U.S. Dept. of Energy Basic Energy Sciences.

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Spectroscopic Research of Pt + NH 3

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  1. Spectroscopic Research of Pt + NH3 The Search for Polyatomic Molecules 13450 13200 Jamie Gengler, Timothy Steimle, and Jinhai Chen Dept. of Chemistry & Biochemistry Arizona State University, Tempe, AZ 85287 June 21, 2005 Funded by U.S. Dept. of Energy Basic Energy Sciences

  2. Motivations / Objectives • Characterize and model spectra obtained from polyatomic products of Pt + NH3. • Other polyatomic examples:SrNH2, SrCCH, SrNC (University of Waterloo group) • Anticipation of detecting the species PtNH or PtNH2.

  3. Plasma Chemistry and Fluorescence Detection. pre-amp Gated photon counter 20 Hz Nd:YAG 355 nm (10mJ) PMT * Optical filter or Monochromator Lens IEEE computer board # * Platinum rod (rotated by stepper motor) Molecular beam * 20 Hz solenoid pulsed valve 20% NH3 80% Ar 500 psi Mirror 10-6 torr diffusion pump 10-5 torr diffusion pump (variable time delay) CW Titanium sapphire 750 nm * * D/A computer board Burleigh wavemeter RS232 serial computer board 1 RS232 serial computer board 2 #

  4. Results of Previous Work. • K.Y. Jung, T.C. Steimle et al, J. Chem. Phys.102 (2): 643-652 Jan. 8 1995. 1 4 3 2 Features 1 and 3 are unknown. Features 2 and 4 were assumed polyatomic in nature.

  5. Results of Previous Work. • K.Y. Jung, T.C. Steimle et al, J. Chem. Phys.102 (2): 643-652 Jan. 8 1995. TABLE I. The predicted ab initio properties of PtN. State Re(Å) Te(cm-1) we(cm-1) me(D) X2P 1.774 0 821 1.956 a4S- 1.844 975 749 2.784 A2S- 1.880 3431 710 2.661 b4D 1.928 5554 639 2.431 B2D 1.955 7474 564 2.255 C2D(II) 1.854 11040 993 D2S+ 1.829 13373 893 c4P 2.080 14266 459 E2D(III) 1.885 17578 740 d4P(II) 1.923 18167 806 0.649

  6. Dispersed Fluorescence (next 2 slides) Unpublished Results. Low resolution spectra of Pt + NH3. Other reagents (CH3CN, NO, N2, …) produce no spectra! 13440 13250 12435 13120 ??? 13450 12400

  7. Unpublished Results. Laser Line Laser Line 945 cm-1 n1 n1 This molecule is probably PtN!

  8. Unpublished Results. Laser Line Laser Line n1 940 cm-1 n1 This molecule is probably PtN!

  9. Results of Previous Work. • K.Y. Jung, T.C. Steimle et al, J. Chem. Phys.102 (2): 643-652 Jan. 8 1995. TABLE I. The predicted ab initio properties of PtN. State Re(Å) Te(cm-1) we(cm-1) we(cm-1)a me(D) X2P 1.774 0 821 947 1.956 a4S- 1.844 975 749 2.784 A2S- 1.880 3431 710 2.661 b4D 1.928 5554 639 2.431 B2D 1.955 7474 564 2.255 C2D(II) 1.854 11040 993 D2S+ 1.829 13373 893 c4P 2.080 14266 459 E2D(III) 1.885 17578 740 d4P(II) 1.923 18167 806 0.649 a Observed value. E.J. Friedman-Hill and R.W. Field, J. Chem. Phys. 100 (9), May 1, 1994

  10. 210 cm-1 n3 440 cm-1 650 cm-1 n2 n1 Unpublished Results. Laser Line Laser Line n1 n2 n3 This molecule cannot be PtN!

  11. Platinum Dimer. Pt Pt ni = Ei – E0 where Ei = we(vi + ½) + wexe(vi + ½)2 Compare these to literature values: we = 222 cm-1 wexe = 0.6 cm-1 M.D. Morse et al, J. Chem Phys., 115 (16), 7543(2001) we = 218 ± 21cm-1 wexe = -0.2 ± 5.7cm-1 Band near 13255.5 cm-1 has already been assigned as Pt2. M.D. Morse et al, J. Chem Phys., 89 (9), 5517 (1988)

  12. Laser Line n4 445 cm-1 n3 655 cm-1 877 cm-1 n2 n1 1095 cm-1 Unpublished Results. Laser Line n1 n2 n3 n4 This molecule cannot be PtN!

  13. 195Pt 194Pt Natural Abundances: 194Pt = 32.9% 195Pt = 33.8% 196Pt = 25.3% 198Pt = 7.2% 0.2 cm-1 0.2 cm-1 0.2 cm-1 196Pt 198Pt Unpublished Results. 13439.80 13440.50

  14. 13440 Pt + ND3 Unpublished Results. Could this molecule be PtNHx? Pt + NH3 13440 13500 13400

  15. Unpublished Results. Could this molecule be PtNHx? No!! Pt + NH3 Pt + ND3 Photon Counts 13440.00 13440.25 -1 Wavenumber (cm )

  16. Platinum Dinitrogen? Obs. frequencies (in solid Ar): 2168.5 cm-1 (n1), 499.6 cm-1 (n2) A. Citra et al, J. Phys. Chem. A105, 7799 (2001) 2V = k1(DrNN)2 + k2(DrPtN)2 + k3(Df)2 445 cm-1 n2 In matrix form: |GF – l| = 0 655 cm-1 2n3 877 cm-1 2n2 Calculated nitrogen isotope shifts: Dn1 = 80.11 cm-1 Dn2 = 19.47 cm-1 Dn3 = 15.88 cm-1 1095 cm-1 n2+2n3

  17. Unpublished Results. Could this molecule be PtN2? No!! Pt + 14NH3 Pt + 15NH3 Photon Counts 13440.15 13440.30 Wavenumber (cm-1)

  18. Platinum Dimer. M.D. Morse et al, J. Chem Phys., 89 (9), 5517 (1988)

  19. 13440 cm-1 Pt2 System VIII 1-0 0-0 13250 cm-1 M.D. Morse et al, J. Chem Phys., 115 (16), 7543 (2001) M.D. Morse et al, J. Chem Phys., 89 (9), 5517 (1988) Platinum Dimer. 13440 cm-1 Dispersed Fluorescence 0 2 4 we/~ 187cm-1 13450 wavenumber (cm-1) 13200 13700 wavenumber (cm-1) 12050

  20. Pt2 System XVIII (n00~ 17914 cm-1) 3-0 we/~ 171 cm-1 4-0 Results of Previous Work. • K.Y. Jung, T.C. Steimle et al, J. Chem. Phys.102 (2): 643-652 Jan. 8 1995. 18400 18500 18600 Laser wavenumber

  21. Platinum Dimer Chemistry. • Pt2 (as well as PtN) spectra disappear unless NH3 is used. Why?? • Proposed chemical chain reaction: • 2Pt* + 2NH3 2PtN + 3H2 • 2PtN Pt2 + N2 DE ~ -5.22eV • 2) Proposed metal cluster 3-body collision1 facilitated by NH3 • chemisorption to Pt2: • 2Pt* + :NH3 Pt* :NH3 Pt* Pt* :NH3 Pt2 + NH3* (or fragments) Pt* • Michael D. Morse, “Supersonic Beam Sources”, Experimental Methods in the Physical Sciences, 29B, 735 (1996) • M. Garcia-Hernandez et al, Surface Science, 430, 18 (1999)

  22. Conclusions. • PtN2 in abstract is actually Pt2. • First known metal dimer/cluster formation facilitated by a reagent (NH3). Department of Chemistry and Biochemistry

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