Transcript mss2005 AuO.ppt

Fourier Transform
Spectroscopy of AuO
Leah C. O’Brien* and Sarah C. Hardimon
Department of Chemistry
Southern Illinois University Edwardsville
James J. O’Brien
Department of Chemistry and Biochemistry
and Center for Molecular Electronics
University of Missouri – St. Louis
Previous Work on AuO
• AuO not observed previously in gas phase
• AuO observed in rare gas matrices [Griffiths
and Barrow]
• T~25000 cm-1
• ~600 cm-1
• ~675 cm-1
• Au-O bond energy, ~3 eV, determined by glow
discharge mass spectrometry [Hecq et al.]
• Ab initio calculations on electronic structure
[Schwerdtfeger et al.]
Electronic Structure of AuO
• Ionic character,
Au+O• Ground state 2Πi
• [Au+]2σ22π3
• Low-lying A 2Σ+
• [Au+]2σ12π4
• Other transitions
from 2σ or 2π to 3σ
• Predict
Aso(2Πi)= -1000 cm-1
• GOAL: record and
analyze 2Σ+ - X 2Πi
transition of AuO
100% Au
0% O
100% Au
0% O
0% Au
100% O
0% Au
100% O
Fenske-Hall calculation
Previous Work on Related Molecules
• Near infrared 2Σ+ - X 2Πi transitions
•
•
•
•
CuO: Aso(2Π) = -276 cm-1, T0(2Σ+) = 7715 cm-1
CuS: Aso(2Π) = -433 cm-1, T0(2Σ+) = 10551 cm-1
CuSe: Aso(2Π) = -1592 cm-1, T0(2Σ+) = 11286 cm-1
AgO: Aso(2Π) = -269 cm-1, T0(2Σ+) = 8294 cm-1
• Predictions for AuO 2Σ+ - X 2Πi transition
• Aso(X 2Π) = -1000 cm-1 (our calculation, based on
eigenvector of valence 2p orbital: ~80% O 2p and
~20% Au 5d character)
• T0(2Σ+) = 10800 cm-1 (Schwerdtfeger et al.)
Procedure
• Used FT spectrometer associated with
McMath-Pierce National Solar Observatory at
Kitt Peak, AZ, to record emission spectrum.
• AuO molecules produced in a Neon-based
electronic discharge using a gold-lined hollow
cathode with a trace amount of oxygen.
• The FT spectrometer configured with a CaF2
beamsplitter and liquid-nitrogen cooled InSb
detectors to record the 4000-12000 cm-1
region.
Results
• Two red-degraded bands observed
• Bandheads located at 10660 and 10720 cm-1
• Bands separated by ~60 cm-1
• Line positions and line widths were fit to a Voigt profile
using the program GREMLIN
• Two R-type branches and two P-type branches observed in
each band.
• No isotopomer structure (197Au is 100% abundant)
• Probably is AuO
• Definitely not 2Σ+ - X 2Πi transition!!
AuO Spectrum
Results
• Band structure (2 P-branches and 2 Rbranches) is consistent with sub-band(s)
of 2,4Π –2,4Π transition
• Assume ground state (X 2Π3/2) is
involved. Two possible assignments:
1. Π3/2 – X 2Π3/2 and Π1/2 – X 2Π1/2
or
2. Vibrational sequence of Π3/2 – X 2Π3/2
Results
• Fitted data from both bands to Π3/2 – 2Π3/2
• T = Tv + BvJ(J+1) – DvJ2(J+1)2 ± 0.5 qJJ(J+1)(J+0.5)
Tv
Bv
Dv x 106
qJ x 105
P3/2 v=1
ΔG½+10659.4693(15
)
0.290549(13)
0.4276(22)
-0.950(12)
P3/2 v=0
10721.1417(10)
0.2944500(76)
0.4113(10) -0.9393(66)
X 2P3/2 v=1
ΔG½
0.308145(13)
0.4069(24)
X 2P3/2 v=0
0.0
0.3116291(76)
0.3999(10) -0.4695(66)
-0.481(12)
• Constants consistent with vibrational sequence
• Bands assigned as (0,0) and (1,1) vibrational
bands of [10.7] Π3/2 – X 2Π3/2
Results
• Absolute numbering of vibrational bands is not
definitive
• for example, (1,0) and (2,1), or (0,1) and (1,2)
• Bond lengths
• Be= 0.313373(8) cm-1
• re = 1.9069 Å


Be= 0.296402(8) cm-1
re = 1.9607 Å
• Relativistic calculations
• Schwerdtfeger et al.: re = 1.946 Å
• Seminario et al.:
re = 1.925 Å
Relativistic Effects
• Compare bond
lengths of CuO,
AgO, and AuO
• Valence σ molecular
orbital has
considerable Au 6s
character
2.4
2.2
2.0
CuO
AgO
AuO
1.8
1.6
1.4
1.2
r0
Photoelectron Spectrum of AuO- and AuO
• Recent photoelectron spectrum from
Lineberger’s group
• Complementary data:
We
Bond length
Vibrational sequence
Transition energy
They
Spin-orbit
Vibrational progression
Electron affinity
New calculations*
New Calculations*
• MOLPRO 2002.3, Ichino et al.
•
•
•
•
re(X 2Π) = 1.907 Å (expt=1.9069 Å)
Te(A 2Σ+)= 10400 cm-1
re= 1.874 Å
Te(a 4Π) = 16800 cm-1
Te(B 2Π) = 27200 cm-1
• Implications
• Our new [10.7] Π3/2 state is probably the a 4Π 3/2 state
• The A 2Σ+ - X 2Πi transition should have blue-degraded
bands (as seen in CuO and AgO); probably occurs in
the near-infrared somewhere < 10700 cm-1
• The transition observed by Griffiths and Barrow at
25000 cm-1 could be the B 2Πi - X 2Πi
Conclusions
• Gas phase AuO observed for the first time
• (0,0) and (1,1) vibrational bands of the new
[10.7] Π3/2 – X 2Π3/2 transition of AuO analyzed
• Recently published:
• L.C. O’Brien, S.C. Hardimon, and J.J. O’Brien,
“Spectroscopy of AuO: Identification of the [10.7]
Π3/2 – X 2Π3/2 Transition,” J. Phys. Chem. A 108,
11302-11306 (2004).
• T. Ichino, A.J. Gianola, D.H. Andrews, and W.C.
Lineberger, “Photoelectron Spectroscopy of AuOand AuS-,” J. Phys. Chem. A 108, 11307-11313
(2004).
Acknowledgements
NSF – funding
Mike Dulick – technical support at Kitt
Peak
Takatoshi Ichino and Carl Lineberger –
sharing preliminary data and insightful
discussions regarding the PES data