Spectroscopic detection of silicon carbides Neil J Reilly

Spectroscopic detection of silicon carbides Neil J. Reilly, Damian L. Kokkin, Michael C. Mc. Carthy and Patrick Thaddeus Harvard-Smithsonian Centre for Astrophysics John F. Stanton University of Texas at Austin Ryan C. Fortenberry and T. Daniel Crawford Virginia Tech $$ NSF NASA $$

Silicon-containing molecules in space 2 atoms 3 atoms 4 atoms 5 atoms Si. C c-Si. C 2 c-Si. C 3 C 4 Si Si. N Si. CN Si. O Si. NC Si. S Si. H? Si. H 4

Experiment – R 2 C 2 PI of jet-cooled discharge • Discharge 500 -1500 V • Si. H 4/C 2 H 2 in Ar/Ne • Probed via R 2 C 2 PITOFMS

Si. H 4/C 2 H 2/Ar discharge mass spectrum with 157 nm

Electronic Spectroscopy of Si 3 C C 1 B 1 —X 1 A 1 band R 2 C 2 PI spectroscopy • significant vibrational excitation • fast (~psec) relaxation to triplet state

Electronic Spectroscopy of Si 3 C C 1 B 1 —X 1 A 1 band

Si 3 C C 1 B 1 vibrational frequencies Mode Experimental w 1(a 1) Ab initio 724 w 2(a 1) 529 530 w 3(a 1) 303 305 2 w 4(b 1) 480 518 w 5(b 2) 861 w 6(b 2) 369

R 2 C 2 PI detection of silicon carbides 96 Si 3 C Si 3 84 m/z 80 77 Si 2 C 2 Si. C 4 H 68 Si 2 C

Structures of Sin. Cm ~1. 7 1. 250 135°-110° 40° 1. 812 2. 177 1. 250 78° 2. 743

Optical detection of Si 2 C ~900 cm-1

Optical detection of Si 2 C

Optical detection of Si 2 C ~ 200 cm-1 ~ 50 cm-1 ~ 100 cm-1

Si 2 C theory • Ryan Fortenberry and Dan Crawford (Virginia Tech) using PSI 3 and CFOUR packages • Optimized ground and excited states and vibrational frequencies at CCSD level of theory with aug-cc-p. V(T+d)Z basis set • Vertical excitation energies at ground state geometry by EOM-CCSD (Stanton and Bartlett) - Electronic transition of Si 3 C predicted at 3. 13 e. V and observed at 3. 09 e. V State 1 1 A 1 Vertical Excitation Energy (e. V) Oscillator Strength Adiabatic Excitation Energy 0. 00 Bond Length (Å) Bond Angle (°) 1. 694 116. 0 C 2 v Frequencies (cm-1) w 1(a 1) w 2(a 1) w 3(b 2) 864 151 1251 Exp. 839 166 1188 1 1 B 1 3. 54 0. 0325 3. 27 1. 698 180. 0 561 198 1095 1 1 B 2 3. 91 0. 0123 2. 69 1. 761 180. 0 526 190 1033 2 1 A 1 4. 33 0. 0131 3. 27 1. 698 180. 0 561 199 1090

Optical detection of Si 2 C ~ 200 cm-1 ~ 50 cm-1 ~ 100 cm-1 tf ~ 300 ns

R 2 C 2 PI detection of Si. C 4 H B 2 S - X 2 PW (c. f. C 5 H ~ 20500 cm-1) Direct measurement of S-O splitting ~ 60 cm-1 (c. f. Si. CCH ~ 70 cm-1)

Optical detection of Si 2 C 2 C C Si Si Si C C Si

Conclusions • First optical detections of – Si 2 C 2 – Si. C 4 H • Require fluorescence spectra • Optical detection of Si 2 C in space? – Strongest bands likely near 350 nm, require hottest carbon star in which M-S bands of Si. C 2 are still strong