Download Si3_Final

The 66th International Symposium
on Molecular Spectroscopy, June 2011
Visible spectrum of Si3
Xiujuan Zhuang and Timothy C. Steimle*
Department of Chemistry and Biochemistry
Arizona State University, Tempe,AZ 85287
Neil Reilly, Damian Kokkin & Michael McCarthy *
Harvard-Smithsonian Center for Astrophysics
Varun Gupta & John P. Maier
Dept. of Chem. Univ. of Basel, Basel, Switzerland
‡
John F. Stanton *
Chemistry & Biochemistry
U. Texas- Austin
T.D. Crawford & R. Fortenberry
Chemistry Department
Virginia Tech.
* Funded by NSF.
‡
Swiss National Science Foundation
Key Previous studies (Exp.)
Kitsopoulos et al (Neumark group), JCP, v93, 6108 (1990)
PES on Si3- 3A’2 (D3h) 2 (e) = 36040 cm-1
Arnold & Neumark, JCP, v100, 1797 (1994)
ZEKE on Si3- 3A’2 (D3h) 1(a1), 2 (e) =50110 cm-1 ,337 10 cm-1
Li, VanZee, Weltner and Raghavachari, Chem Phys. Lett., v243, 275 (1995)
Matrix isolation, Infrared absorption. X1A1 (C2v)1 550 cm-1, 3 525 cm-1,
Fulara, Freivogel Gutter and Maier, J. Phys. Chem. v100, 18042 (1996)
Matrix isolation, Visible absorption. X1A1 (C2v)
McCarthy & Thaddeus, Phys. Rev. Lett., v190, 213003 (2003)
Pure Rot. in X1A1 (C2v) 2  146 cm-1, R=2.177 Å &  =78.10`
Key Previous studies (Theory)
Rohfling & Raghavachari, JCP, v96, 2114 (1992)
X1A1 (C2v) 1, 2, 3 = 551(a1), 148 (a1), 525(b2) cm-1
3A’2 (D3h) 1, 2, = 522 (a1), 285 (e) cm-1
Garcia-Fernandez, Boggs & Stanton JCP, v126, 074305 (2007)
 1E1 (D3h) Jahn-Teller distort
 X1A1 (C2v) 1, 2, 3 = 596(a1),196 (a1), 540(b2) cm-1
& 3A’2(D3h) 1, 2, = 522 (a1), 327 (e) cm-1
Garcia-Fernandez, Boggs & Stanton JCP, v126, 074305 (2007)
Starting point : D3h molecule:
Config. 1
Config. 2
….4s23p2 (Si)
D3h
3A’
1A
1
& 1B2
1A
1
& 1B2
21E’
1A
1
1 & B2
3E’’
1A
2
& 1B1
1A
2
& 1B1
1A
1’
1E’’
Config. 4
Si3((a’1)2(a”2)2(e’)1(e”)1)
3E’’
1E’’
1,3A
1,3A
Mainly “3p”
2
11E’
3E’
Config. 3
C2v
Mainly “4s”
1’’
2’’
1A
& 1B1
1A & 1B
2
1
2
12 low-lying states
E < 1. 0 eV
Excites states
E > 2.0 eV
J.F. Stanton
Unpublished
Garcia-Fernandez, Boggs & Stanton JCP, v126, 074305 (2007)
Singlet manifold
1A
1
1B
Triplet manifold
3B
1
3A
1
1
X1A1
D3h
D3h
1500
Jahn-Teller distorted to C2V states
Energy (cm-1)
=522 cm1
=327 cm1
=540 cm1
=569 cm-1
0
=196 cm-
~1
X
A1
1
Visible spectrum -Preliminaries
e”
e’
a”2
a’1
Transitions in the visible/ uv
Shuffle
electrons
amongst these
12 low-lying
electronic states
Ne-matrix absorption
Maier’s group.
J Phys Chem. 1996
Experimental method-Basel & Harvard- Smithsonian
Mass-Selected REMPI
SiH4
&
He
Pulse
valve
•skimmer
MCP
Ion Detector
ArF (193 nm) laser
Pulsed HV
Pulsed OPO or Dye laser
Resolution 0.3 cm-1
Experimental method-ASU
Box-car integrator
Photon
counting
Pulse
valve
PMT
PMT
Monochromator
SiH4
&
He
Pulsed HV
Well collimated
molecular beam
Rot.Temp.<20 K
Pulsed dye laser
Resolution 0.2 cm-1
Si3- Mass-selected REMPI
“Hot”
“Cold”
The goal is to assign this optical spectrum!
Laser Excitation Spectrum- ASU
High temp. Mass-selected
REMPI
LIF Signal
B
A
C D
Laser Wave Number
A
Si3
B
Si3
C
Si3 &
??
D
Si3
Dispersed LIF Spectra
Garcia-Fernandez, Boggs & Stanton JCP, v126, 074305 (2007)
 X1A1 (C2v) 1, 2, 3 = 596 (a1), 196 (a1), 540 (b2) cm-1
 a3A’2(D3h) 1, 2, = 522 (a1), 327(e) cm-1
Dispersed LIF Spectra
Not Si3
Garcia-Fernandez, Boggs & Stanton JCP, v126, 074305 (2007)
 X1A1 (C2v) 1, 2, 3 = 596(a1) ,196 (a1), 540(b2), cm-1
 a3A’2(D3h) 1, 2, = 522 (a1), 327(e) cm-1
??
SiH2
High temp. Mass-selected
REMPI
Assignment
LIF Signal
B
Si3
A Si3
C D
Laser Wave Number
13A”1
(D3h)
Si3
Ab initio predictions;
EOM-CCSD
(e)=1 (a1’)=0
(e)=0 (a1’)=0
A B D
D
(e)=1 (a1’)=0
3A’
2
(D3h)
A
B
(e)=0 (a1’)=0
a)
b)
c)
2.31
This work;
ZEKE
Tentative assign of REMPI
The 173 cm-1 progression in DF following 0 00 a3A’2 (D3h)
13A”1 (D3h)
Laser
0 00
????
13A”1
Singlet System
(D3h)
(e)=0 (a1’)=0
Intersystem
crossing
0 00
2(a1)>> 0
3A’
2 (D3h)
(e)=0 (a1’)=0
~1
X A1 (C2v)
Evidence for Intersystem Crossing Mechanism:
DF
Monochromator
Viewing 
Laser excitation spectrum viewed through monochromator
a3A’2 (D3h) 13A” (D )
1
Si3
Si3
3h
SiH2
Evidence for Singlet Transitions in the Excitation Spectra
REMPI
LIF Signal
Ion signal
Based on Ab initio (Stanton,
unpublished) results & Ne
matrix results
B
A
Not detected by LIF !
C D
Laser Wave Number
Summary
1. First recording of the visible spectrum of gas-phase Si3
2. Dominated by transitions in the triplet D3h form.
3. Evidence for intersystem crossing from triplet D3h to singlet C2v
4. Singlet system is absent from LIF but is in REMPI
5. Unable to detect high-resolution LIF (Not discussed)
Thank You !