Spectroscopic Research of Pt + NH3

The Search for Polyatomic Molecules

Jamie Gengler, Timothy Steimle, and Jinhai Chen

Dept. of Chemistry & Biochemistry

Arizona State University, Tempe, AZ 85287

June 21, 2005

Wavenumbers

Phot

on C

ount

s

13450 13200

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.

20% NH3

80% Ar

500 psi

10-6 torr

diffusion pump

10-5 torr

diffusion pump

Platinum rod (rotated by stepper motor)

20 Hz Nd:YAG

355 nm (10mJ)

CW

Titanium

sapphire

750 nm

PMT

LensOptical filter

or Monochromator

Mirror

Molecular beam

20 Hz solenoid pulsed valve

pre-ampGated photon

counter

IEEE computer

board

*

*

*

D/A computer

board

*

*(variable time delay)

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.

12

3 4

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) e(cm-1) e(D)

X2 1.774 0 821 1.956a4- 1.844 975 749 2.784A2- 1.880 3431 710 2.661b4 1.928 5554 639 2.431B2 1.955 7474 564 2.255C2(II) 1.854 11040 993D2+ 1.829 13373 893 c4 2.080 14266 459E2(III) 1.885 17578 740d4(II) 1.923 18167 806 0.649

Unpublished Results.

13440

13250

13120

Wavenumber (cm-1)

Phot

on C

ount

s

12435

Low resolution spectra of Pt + NH3.

???

13450 12400

Other reagents (CH3CN, NO, N2, …) produce no spectra!

Dispersed Fluorescence (next 2 slides)

Unpublished Results.

Angstroms7900 8100 8300 8500 8700 8900 9100

Phot

on C

ount

s

12435 cm-1 Dispersed Fluorescence

1

Laser Line

Laser Line

1

945 cm-1

This molecule is probably PtN!

Unpublished Results.

Angstroms7500 7700 7900 8100 8300 8500

Phot

on C

ount

s

13120 cm-1 Dispersed Fluorescence

Laser Line

1

1940 cm-1

This molecule is probably PtN!

Laser Line

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) e(cm-1) e(cm-1)a e(D)

X2 1.774 0 821 947 1.956a4- 1.844 975 749 2.784A2- 1.880 3431 710 2.661b4 1.928 5554 639 2.431B2 1.955 7474 564 2.255C2(II) 1.854 11040 993D2+ 1.829 13373 893 c4 2.080 14266 459E2(III) 1.885 17578 740d4(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

Unpublished Results.

Angstroms7300 7500 7700 7900 8100

Phot

on C

ount

s

13250 cm-1 Dispersed Fluorescence

Laser Line

1

23

1

2

3

Laser Line

210 cm-1

440 cm-1

650 cm-1

This molecule cannot be PtN!

Platinum Dimer.

i = Ei – E0 where Ei = e(vi + ½) + exe(vi + ½)2

e = 218 ± 21cm-1

exe = -0.2 ± 5.7cm-1

Compare these to literature values:

e = 222 cm-1

exe = 0.6 cm-1

M.D. Morse et al, J. Chem Phys., 115 (16), 7543 (2001)

Band near 13255.5 cm-1 has already been assigned as Pt2.M.D. Morse et al, J. Chem Phys., 89

(9), 5517 (1988)

Pt Pt

Unpublished Results.

Laser Line

1 2

3 4

Angstroms7300 7500 7700 7900 8100 8300

Phot

on C

ount

s

13440 cm-1 Dispersed Flourescence

1

2

3

4

Laser Line

445 cm-1

655 cm-1

877 cm-1

1095 cm-1

This molecule cannot be PtN!

Wavenumber (cm-1)

Phot

on C

ount

s

13440 cm-1 High Resolution

0.2 cm-1 0.2 cm-1 0.2 cm-1

13440.5013439.80

Unpublished Results.

Natural

Abundances:194Pt = 32.9%195Pt = 33.8%196Pt = 25.3%198Pt = 7.2%

198Pt

196Pt

194Pt195Pt

Unpublished Results.

Could this molecule be PtNHx?

Wavenumber (cm-1)

Phot

on C

ount

s

13500 13400

Pt + NH3

13440Pt + ND313440

Unpublished Results.

Could this molecule be PtNHx?

Wavenumber (cm-1)

Phot

on C

ount

s

13440.00 13440.25

Pt + NH3

Pt + ND3

No!!

Platinum Dinitrogen?

Pt N NrPtN rN N

2V = k1(rNN)2 + k2(rPtN)2 + k3()2

In matrix form:

|GF – | = 0Calculated nitrogen isotope shifts:

1 = 80.11 cm-1

2 = 19.47 cm-1

3 = 15.88 cm-1

Obs. frequencies (in solid Ar):

2168.5 cm-1 (1), 499.6 cm-1 (2)A. Citra et al, J. Phys. Chem. A 105, 7799 (2001)

Angstroms7300 7500 7700 7900 8100 8300

Phot

on C

ount

s

13440 cm-1 Dispersed Flourescence

445 cm-1

655 cm-1

877 cm-1

1095 cm-1

2

3

2

23

Unpublished Results.

Could this molecule be PtN2? No!!

Pt + 14NH3

Pt + 15NH3

13440.15 13440.30Wavenumber (cm-1)

Phot

on C

ount

s

Platinum Dimer.

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

Platinum Dimer.

M.D. Morse et

al, J. Chem

Phys., 115

(16), 7543

(2001)

0 42

13440 cm-1 Dispersed Fluorescence13440 cm-1

13250 cm-1

Pt2 System VIII 0-01-0

wavenumber (cm-1)13450 13200

e/ ~ 187cm-1

wavenumber (cm-1)13700 12050

M.D. Morse et

al, J. Chem

Phys., 89 (9),

5517 (1988)

Results of Previous Work.K.Y. Jung, T.C. Steimle et al, J. Chem. Phys. 102 (2): 643-652 Jan. 8 1995.

Laser wavenumber18400 1860018500

Pt2 System XVIII (00 ~ 17914 cm-1)

3-0 4-0e/ ~ 171 cm-1

Platinum Dimer Chemistry.

Pt2 (as well as PtN) spectra disappear unless NH3 is used. Why??

1) Proposed chemical chain reaction:

2Pt* + 2NH3 2PtN + 3H2

2PtN Pt2 + N2 E ~ -5.22eV

2) Proposed metal cluster 3-body collision1 facilitated by NH3

chemisorption to Pt2:

2Pt* + :NH3

Pt*Pt*

:NH3

1) Michael D. Morse, “Supersonic Beam Sources”, Experimental Methods in the Physical Sciences, 29B, 735 (1996)

2) M. Garcia-Hernandez et al, Surface Science, 430, 18 (1999)

M a ss

Ion

dete

ctor

sign

al (v

olts

)

I r

I rN

IrN (N H )3

1 8 0 2 0 0 2 2 0 2 4 0 2 6 0 2 8 0 3 00-0 .0 1 4

-0 .0 1 2

-0 .0 1 0

-0 .0 0 8

-0 .0 0 6

-0 .0 0 4

-0 .0 0 2

0 .0 0 0

0 .0 0 2

IrN (N H )3 3IrN (N H )3 2

IrN (N H )3 4

Pt*Pt*

:NH3 Pt2 + NH3* (or fragments)

Conclusions.

PtN2 in abstract is actually Pt2. First known metal dimer/cluster formation

facilitated by a reagent (NH3).

Department of Chemistry

and Biochemistry

T.M aT.Ste im le

J .C he nJ . G e ng le r

W. Virg oR.Sm ith

A. M a rtin