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

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.

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 #

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.

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

Unpublished Results.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

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 Unpublished Results.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

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 Unpublished Results.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

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

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 Unpublished Results.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

Pt Pt Platinum Dimer. 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)

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 Unpublished Results.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

Unpublished Results. 0.2 cm-1 13439.80 13440.50 195Pt 194Pt Natural Abundances: 194Pt = 32.9% 195Pt = 33.8% 196Pt = 25.3% 198Pt = 7.2% 198Pt 196Pt 194Pt 195Pt 0.2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

Unpublished Results.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

Unpublished Results.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

Platinum Dinitrogen? Obs. frequencies (in solid Ar): 2168.5 cm-1 (n1), 499.6 cm-1 (n2) A. Citra et al, J. Phys. Chem. A 105, 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

Unpublished Results.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

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

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

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

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)

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