Communication: A vibrational study of titanium dioxide cation using the vacuum ultraviolet laser pulsed field ionization-photoelectron method

We have successfully measured the vacuum ultraviolet (VUV) laser photoionization efficiency and pulsed field ionization-photoelectron (PFI-PE) spectra of cold titanium dioxide (TiO2) prepared by a supersonically cooled laser ablation source. The VUV-PFI-PE spectrum thus obtained exhibits long progressions of the v(2)(+)(a(1)) bending and the combination of v(1)(+)(a(1)) stretching and v(2)(+)(a(1)) bending vibrational modes of the TiO2+((X) over tilde B-2(2)) ion. The pattern of Franck-Condon factors observed indicates that the O-Ti-O bond angle of the TiO2+((X) over tilde B-2(2)) ion is significantly different from that of the TiO2((X) over tilde (1)A(1)) neutral, whereas the change of the Ti-O bond distance is very minor upon the photoionization transition. The analysis of the PFI-PE bands has made possible the determination of the adiabatic ionization energy for TiO2, IE(TiO2) = 77215.9 +/- 1.2 cm(-1) (9.57355 +/- 0.00015 eV), the harmonic vibrational frequencies, omega(+)(1) = 829.1 +/- 2.0 cm(-1) and omega(+)(2) = 248.7 +/- 0.6 cm(-1), and the anharmonic coefficients, chi(+)(11) = 5.57 +/- 0.65 cm(-1), chi(+)(22) = 0.08 +/- 0.06 cm(-1), and chi(+)(12) = -4.51 +/- 0.30 cm(-1) for the TiO2+((X) over tilde B-2(2)) ground state. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4789792]