Vibronic structure of TiO+ from multiphoton ionization photoelectron spectroscopy

Abstract

We apply the techniques of resonance enhanced multiphoton ionization (REMPI) and time-of-flight photoelectron spectroscopy (TOF-PES) to TiO molecules cooled in a pulsed nozzle expansion to obtain vibronic spectra of gas phase TiO+. The adiabatic first ionization energy is refined to I1(TiO)=54 999±52 cm−1=6.819±0.006 eV, which yields D0(Ti+–0) =159.9±2.2 kcal/mol. For the X 2Δ state of TiO+, we resolve spin–orbit pairs of vibrational levels for v=0–14, yielding ωe=1045±7 cm−1 and ωexe =4±1 cm−1. The spin–orbit splitting ΔEso =210±6 cm−1 permits confirmation of the state symmetry by comparison with the known spin–orbit splittings of the X 3Δ state of TiO. We also observe a new excited B 2∑+ state at T0=11 227±17 cm−1 with ωe =1020±9 cm−1 and ωexe =6±2 cm−1. This state is distinct from the A 2∑+ state (average frequency 860±60 cm−1) previously observed by Dyke and co-workers. From components of certain PESs apparently due to one or more metastable states of TiO, we infer the existence of a previously unobserved state of neutral TiO at T0=2980 cm−1, possibly the 3∑− state. Finally, we discuss the electronic structure and vibrational frequencies of TiO, TiO+, and other third row metal oxides from both molecular orbital and ligand field points of view in order to understand the ordering of electronic states and certain trends in vibrational frequencies. The molecular orbital model readily explains why nominally isoelectronic neutral and cationic metal oxides, such as TiO+ and ScO, are electronically quite dissimilar.

Ionization potentials and bond energies of TiO, ZrO, NbO and MoO

“…5 The proposed best values from these studies were IP͑NbO͒ϭ7.91͑2͒ eV and IP͑TiO͒ϭ6.82͑2͒ eV. Later Sappey et al 6 obtained IP͑TiO͒ϭ6.819͑6͒ eV from a multiphoton ionization photoelectron spectrum in excellent agreement with the previous measurements. The accuracy of their value was limited by the ionization potential of the titanium atom, which was assumed to be 55010Ϯ50 cm Ϫ1 as opposed to the currently accepted value 7 of 55072.5(3) cm Ϫ1 .…”

“…50 The B 3 ⌸ϪX 3 ⌬ system that was used to prepare the intermediate state has been previously studied in some detail 17,44,51 and both states are well characterized. The electronic states of TiO ϩ have been studied using multiphoton ionization photoelectron spectroscopy and the vibrational structure of the ground X 2 ⌬ state, the A 2 ⌺ ϩ , and the B 2 ⌺ ϩ states has been described by Sappey et al 6 By measuring the kinetic energy of those electrons that correlate to the X 2 ⌬ (v ϩ ϭ0) level they could determine the adiabatic ionization potential of TiO. The photoelectron signal arising from the different electronic levels of the Ti atom served as a calibration of the kinetic energy spectra.…”

The E3Π–X3Δ Transition of Jet-Cooled TiO Observed in Absorption

“…The experimental results are consistent with ab initio calculations of the properties of the low-lying electronic states. Among the conclusions to be drawn from the latter is that the δ 2 D 3 − state cannot lie as low as had been thought from the photoelectron spectrum (17) and that its assignment (9) to a new electronic state at 12 284 cm −1 is much more convincing.…”

“…Sappey et al (17) claimed evidence for this state at 2980 ± 40 cm −1 in their photoelectron spectrum, while Barnes et al (9) later assigned it to the lower state of a band observed in dispersed laser-induced fluorescence spectra following excitation to levels of Interestingly, before either of these reports, a weak absorption at 12 250 cm −1 was noted in low-temperature matrix spectra by both McIntyre et al (14) and Powell et al (18) The band is not part of the E-X system, although it occurs in the same region, and was not previously assigned. However, allowing for a matrix shift of approximately 35 cm −1 (not unreasonable), it would support the higher assignment for the δ 2 3 − state, given some mechanism for the observation of the forbidden D 3 − -X (20), hence providing a plausible mechanism for the observation of the forbidden D-X transition in rare gas matrices.…”

Postionization of molecules desorbed from surfaces by keV ion bombardment with femtosecond laser pulses

“…When comparing signal intensities in the postionization and positive SIMS spectra (not shown) the TiO:Ti ratio is over a factor of four greater in the former. Taking into consideration that the ionization potential for the oxide 33 is nearly identical to the metal 34 and that the initial monolayer should contain a high concentration of TiO, surface analysis utilizing postionization provides a quantitative representation of the surface composition.…”