1. * Funded by NSF. 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. Visible spectrum of Si 3 The 66 th International Symposium on Molecular Spectroscopy, June 2011 ‡ Swiss National Science Foundation

2. Key Previous studies (Exp.) Key Previous studies (Theory) Rohfling & Raghavachari, JCP, v96, 2114 (1992)  X 1 A 1 (C 2v )  1,  2,  3 = 551(a 1 ), 148 (a 1 ), 525(b 2 ) cm -1  3 A’ 2 (D 3h )  1,  2, = 522 (a 1 ), 285 (e) cm -1 Garcia-Fernandez, Boggs & Stanton JCP, v126, 074305 (2007)  1 E 1 (D 3h ) Jahn-Teller distort  X 1 A 1 (C 2v )  1,  2,  3 = 596(a 1 ),196 (a 1 ), 540(b 2 ) cm -1 & 3 A’ 2 (D 3h )  1,  2, = 522 (a 1 ), 327 (e) cm -1 McCarthy & Thaddeus, Phys. Rev. Lett., v190, 213003 (2003) Pure Rot. in X 1 A 1 (C 2v )  2  146 cm -1, R=2.177 Å &  =78.10  ` Kitsopoulos et al (Neumark group), JCP, v93, 6108 (1990) PES on Si 3 - 3 A’ 2 (D 3h )  2 (e) = 360  40 cm -1 Arnold & Neumark, JCP, v100, 1797 (1994) ZEKE on Si 3 - 3 A’ 2 (D 3h )  1 (a 1 ),  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. X 1 A 1 (C 2v )  1  550 cm -1,  3  525 cm -1, Fulara, Freivogel Gutter and Maier, J. Phys. Chem. v100, 18042 (1996) Matrix isolation, Visible absorption. X 1 A 1 (C 2v )

3. Garcia-Fernandez, Boggs & Stanton JCP, v126, 074305 (2007) Starting point : D 3h molecule: ….4s 2 3p 2 (Si) Mainly “4s” Mainly “3p” 1 1 E’ 3 A’ 2 1A1’1A1’ D 3h C 2v 1 A 1 & 1 B 2 Config. 2 Config. 3 1 E’’ 3 E’’ 1 A 2 & 1 B 1 Config. 1 2 1 E’ 3 E’ 1 A 1 & 1 B 2 12 low-lying states E < 1. 0 eV 1 A 2 & 1 B 1 Config. 4 Si 3 ((a’ 1 ) 2 (a” 2 ) 2 (e’) 1 (e”) 1 ) 1 E’’ 3 E’’ 1,3 A 1 ’’ 1,3 A 2 ’’ Excites states E > 2.0 eV J.F. Stanton Unpublished

4. Energy (cm -1 ) 0 1500 =522 cm - 1 =327 cm - 1 X1A1X1A1 1B11B1 1A11A1 3B13B1 3A13A1 Jahn-Teller distorted to C 2V states D 3h Garcia-Fernandez, Boggs & Stanton JCP, v126, 074305 (2007) =569 cm -1 =540 cm - 1 =196 cm - 1 X1A1X1A1 Singlet manifoldTriplet manifold ~

5. a” 2 a’ 1 e’ e” Shuffle electrons amongst these 12 low-lying electronic states Transitions in the visible/ uv Ne-matrix absorption Maier’s group. J Phys Chem. 1996 Visible spectrum -Preliminaries

6. Experimental method-Basel & Harvard- Smithsonian Pulsed OPO or Dye laser skimmer Resolution  0.3 cm -1 ArF (193 nm) laser MCP Ion Detector Mass-Selected REMPI Pulse valve SiH 4 & He Pulsed HV

7. Experimental method-ASU Well collimated molecular beam Rot.Temp.<20 K Pulsed dye laser PMT Box-car integrator Pulse valve SiH 4 & He Resolution 0.2 cm -1 Pulsed HV Monochromator PMT Photon counting

8. Si 3 - Mass-selected REMPI “Hot” “Cold” The goal is to assign this optical spectrum!

9. Laser Excitation Spectrum- ASU A B CD LIF Signal Laser Wave Number A B C D High temp. Mass-selected REMPI Si 3 Si 3 & ??

10. Dispersed LIF Spectra Garcia-Fernandez, Boggs & Stanton JCP, v126, 074305 (2007)  X 1 A 1 (C 2v )  1,  2,  3 = 596 (a 1 ), 196 (a 1 ), 540 (b 2 ) cm -1  a 3 A’ 2 (D 3h )  1,  2, = 522 (a 1 ), 327(e) cm -1

11. Dispersed LIF Spectra Not Si 3 ?? Garcia-Fernandez, Boggs & Stanton JCP, v126, 074305 (2007)  X 1 A 1 (C 2v )  1,  2,  3 = 596(a 1 ),196 (a 1 ), 540(b 2 ), cm -1  a 3 A’ 2 (D 3h )  1,  2, = 522 (a 1 ), 327(e) cm -1 SiH 2

12. Ab initio predictions; EOM-CCSD LIF Signal Laser Wave Number A B C D High temp. Mass-selected REMPI Si 3 ABD 3 A’ 2 (D 3h ) 1 3 A” 1 (D 3h ) A B D a)This work; b)ZEKE c)Tentative assign of REMPI Assignment  (e)=1  (a 1 ’)=0  (e)=0  (a 1 ’)=0  (e)=1  (a 1 ’)=0  (e)=0  (a 1 ’)=0 2.31

13. Laser 0 0 0 The 173 cm -1 progression in DF following1 3 A” 1 (D 3h )a 3 A’ 2 (D 3h ) 0 0 0  (e)=0  (a 1 ’)=0 3 A’ 2 (D 3h ) 1 3 A” 1 (D 3h )  (e)=0  (a 1 ’)=0 0 0 0 Intersystem crossing X 1 A 1 (C 2v ) ~  2 (a 1 )>> 0 ???? Singlet System

14. DF Evidence for Intersystem Crossing Mechanism: Monochromator Viewing Laser excitation spectrum viewed through monochromator SiH 2 Si 3 a 3 A’ 2 (D 3h ) 1 3 A” 1 (D 3h )

15. LIF Signal Laser Wave Number A B C D Evidence for Singlet Transitions in the Excitation Spectra Based on Ab initio (Stanton, unpublished) results & Ne matrix results Not detected by LIF ! Ion signal REMPI

16. Summary 1. First recording of the visible spectrum of gas-phase Si 3 2. Dominated by transitions in the triplet D 3h form. 3. Evidence for intersystem crossing from triplet D 3h to singlet C 2v 4. Singlet system is absent from LIF but is in REMPI 5. Unable to detect high-resolution LIF (Not discussed) Thank You !