*Funded by: DoE-BES Xiujuan Zhuang, Timothy C. Steimle & Anh Le Dept. Chem. & BioChem., Arizona State University, Tempe, AZ,USA* The Visible Spectrum of TiO 2 The 65 th International Symposium on Molecular Spectroscopy, June 2010 Ramya Nagarajan, Varun Gupta and John P. Maier Dept. of Chem. Univ. of Basel, Basel, Switzerland ‡ ‡ Swiss National Science Foundation

Motivation B. Astronomy related: TiO  -band TiO  ’-band { { TiO 2  { Annual production > 5.3x10 6 metric tons! Most widely used photo-activated catalysis: Bulk material Supported TiO 2 cluster Molecular A. Catalysis related:

Our Previous Study: PCCP, vol 11, pp 2649 (2009). Goals of present study: a. Assign and simulate the optical spectra b. Improved determination of dipole moment. c. Lifetime measurements. REMPI, LIF, optical Stark and Dispersed LIF of cm -1. Ion counts Next Slide Matrix isolated emission (000)-(000)?

Iso shift=-38 cm -1 Iso shift=+17 cm -1 High res. LIF; optical Stark, dispersed LIF Lifetime measurements

High-resolution LIF cm -1 band    Selected for Optical Stark measurements

Optical Stark spectroscopy on the 2 02  3 03 branch cm -1 band TiO 2

LIF signal Note difference Dispersed Fluorescence of TiO 2

Fluorescent Lifetimes Laser Excitation Wavenumber Lifetime (  sec) Time (nano-sec) LIF signal band Single exponential No obvious pattern

Large variation in Inertial Defect,  = I a -I b -I c Dipole moment of state < that for & state

1) Use of Inertial Defect to Assign Spectrum Vib.Quantum # Harmonic freq. Coriolis coefficient Also Elements of Wilson “G” (Geometry) and “F” (force) matrices. Exp. Info. R e, , & initial guess of assignment (for  i ) Eq. 1 initial guess of assignment (for  i )  vib (predicted)

State cm cm cm -1 assignment (0,1,2)(1,0,0)(1,1,0)  vib (Calc.)  vib (Obs,) (0, 2,0) (0, 2,2) 102 (1, 2,0)

Trends in Radiative Lifetimes

Predicting the spectrum- Franck-Condon factors X 1 A 1 (0,0,0) A 1 B 2 ( 1, 2, 3 ) Two dimensional (2D) overlap integral for the a 1 modes. One dimensional (1D) overlap integral for the b 2 mode. Assuming displaced & distorted harmonic oscillators  Analytical expressions: “2D”: Chang. JCP 128, (2008) “1D”: Chang. JMolSpec 1232, 1021 (2005) Normal coordinates of lower state Normal coordinates of upper state Coordinate of lower state Coordinate of upper state

Predicting spectrum- Franck-Condon factors (Cont.) Need to relate Q(X 1 A 1 ) to Q(A 1 B 2 ). Duschinsky transformation: J =transformation matrix obtained from Normal Coordinated Analyses for the X 1 A 1 to A 1 B 2 states; D=displacement vector Experimental data  Q 1 &Q 2 Normal coor. of X 1 A 1 state Q 1 & Q 2 Normal coor. of A 1 B 2 state “2D” integral : “1D” integral : Need to relate Q 3 (X 1 A 1 ) to Q 3 (A 1 B 2 ): Q 3 (X 1 A 1 ) = Q 3 (A 1 B 2 ) +d 3 d 3 = displacement of non-totally symmetric normal coordinate rigid structure  d 3 =0.

Note: Relative intensity FCF prediction (cont.) FCF d 3 =0 FCF d 3 =0.4

What we have accomplished/measured. Structure for 3 vibrational levels of A 1 B 2. Lifetimes 10 vibrational levels of A 1 B 2. Vibrational frequencies for the X 1 A 1 and A 1 B 2 states. Assigned and simulated the optical spectrum (for > 500 nm). What needs to be done.  el for X 1 A 1 and 3 vibrational levels of A 1 B 2. Assign and simulated the optical spectrum (for <500 nm). Model the vibrational dependence of lifetimes and  el. Rationalize the use of a non-zero displacement for 3 Vibronic Coupling- 3 mode is “misbehaving”

Thank You ! Thanks to Prof. R.W. Field for lecture notes.