Laser Spectroscopy of the C 1 Σ + – X 1 Σ + Transition of ScI ZHENWU LIAO, MEI YANG, MAN-CHOR CHAN Department of Chemistry, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong YE XIA, A. S.-C. CHEUNG Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong 1

Model system for understanding the role of d electrons in chemical bonding Sc: [Ar]3d 1 4s 2, particularly simple with only one electron in the d shell Scandium (Sc) monohalides: only single ionic bonds are formed Motivation Prototype systems for ab-initio calculations only single ionic bonds are formed, amenable to theoretical study 2

Earlier work on ScI Experimental: 1.Fischell et al, Visible spectrum of two low resolution electronic transitions (J. Chem. Phys. 73, 4260 (1980)) 2.Effantin et al, High resolution fluorescence spectra induced by individual laser lines (J. Mol. Spectrosc., 185, 249, (1997)) 3.Taher et al, Fourier transform spectroscopy of B 1 Π – X 1 Σ + Transition (J. Mol. Spectrosc., 189, 220 (1998)) 4.Xia et al, High resolution laser induced fluorescence study of the D 1 Π - X 1 Σ Transition (J. Mol. Spectrosc., 268, 3 (2011)) Theoretical: 1.Bencheikl, Many electronic states predicted by ligand field theory (J. Phys. B: At., Mol. Opt. Phys., 30, L137 (1997)) 2.Reddy et al, RKR potential energy curves for the B 1 Π and X 1 Σ + states (J Quant Spectrosc & Radia Tran, 74, 125 (2002)) 3.Korek et al, 18 low-lying electronic states of ScI obtained by CASSCF and MRCI calculations (J. Quant. Chem., 109, 236 (2009)) 3

Previous studies of ScI High resolution laser induced fluorescence spectroscopy (This work)

Sc I 5p 4s 3d 33 22 11 11 22 11       Electronic ConfigurationsStates (1  ) 2 (1  ) 4 (2  ) 2 X 1  + (1  ) 2 (1  ) 4 (2  ) 1 (1  ) 1 A 1 Δ, a 3 Δ (1  ) 2 (1  ) 4 (2  ) 1 (3  ) 1 C 1  +, c 3  + (1  ) 2 (1  ) 4 (1  ) 1 (3  ) 1 E 1 Δ, e 3 Δ Molecular Orbital Energy Level Diagram Electronic excitation of an electron to the slightly anti-bonding molecular orbital (3  ) results in a weaker chemical bond, i.e., longer bond length and smaller bond strength 5

Experimental Setup 6

7 Laser induced fluorescence (LIF) spectroscopy with monochromator

Monochromator 8 v’ v” Δ G 3/2 Δ G 1/2 Obtain the information about the lower state vibrational separation grating Only LIF signal in a small spectral region is detected by the PMT Play a role as an optical filter Laser Pumping v’ v”

Experimental Conditions Molecules Production: Sc (vapour) + 1% CH 3 I / Ar  ScI + etc. Supersonic Free Jet Expansion: i) backing pressure : 8 atm ii)background pressure: 2×10 -5 Torr Vaporization Laser: Nd: YAG, 10Hz, 1064nm, 24mJ Laser system: DPSS pumped Ti: Sapphire Ring Laser, cm -1 Spectral Linewidth: ~ 0.015cm -1 9

The typical LIF spectrum of the C 1  + – X 1  + transition of ScI Absence of Q branch Shows P and R branches only with P(1) and R(0) as first line Confirms 1  + – 1  + transition 10 The (0,3) band Results and discussion

Observed rovibronic bands in the C 1  + – X 1  + system of ScI 11

Statev T0T0 B10 7 D X1+X1 (6) (7)1.2(1) (8) (1)1.1(2) (8) (1)1.2(1) C1+C1 (4) (1)17.7(5) (7) (8)9.2(1) (7) (8)3.0(1) Molecular Constants for the C 1  + and X 1  + States Molecular constants for the C 1  + state were obtained for the first time Irregularities were observed in both T 0 and B of the C 1  + state, indicated that there should be unseen perturbing state nearby 12

13 The WRF spectrum of the (2,5) band of the C 1  + – X 1  + transition of ScI A series of vibrational levels of the a 3 Δ 1 state were also observed A direct proof that X 1  + and a 3 Δ 1 states are close to each other Pump here

14 Observed rovibronic bands in the e 3 Δ 1 - a 3 Δ 1 system of ScI Effantin et al, High resolution fluorescence spectra induced by individual laser lines (J. Mol. Spectrosc., 185, 249, (1997))

The LIF spectrum of the (0,6) band of the e 3 Δ 1 - a 3 Δ 1 transition of ScI R(1) and P(2) as first line, Ω’= Ω”=1; No Q branch observed due to their weakness The most strongly perturbed transitions are P(12) and R(10), the upper state is perturbed Deperturbation procedures was performed to obtain the molecular constants 15 perturbation

Molecular constants of the e 3 Δ 1, C 1  +, a 3 Δ 1 and X 1  + states 16 Statev o B10 6 D e3Δ1 e3Δ (1)0.5(1) (1)0.2 (1) C1+ C1 (7) (8)0.3(1) (7) (8)0.92(1) (4) (1)1.77(5) a3Δ1a3Δ (2)0.22(1) X1+ X1 (8) (1)0.12(1) (8) (1)0.11(2) (6) (7)0.12(1) † Numbers in parentheses are one standard deviation (in unit of the last figure)

Rotationally resolved LIF spectra of C 1  + -X 1  + and e 3 Δ 1 - a 3 Δ 1 transitions of ScI have been observed and analyzed, and accurate molecular constants were obtained A small perturbation was found in the v = 0 level of the e 3 Δ 1 state, deperturbation procedures were successfully applied to obtain the molecular constants Conclusions 17

18 That’s all. Thank you