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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.

Collisional removal of the v′=0 level of the A 2Σ+ state of the OH radical has been studied as a function of rotational level N′ at room temperature. OH in high rotational levels of the X 2Πi state were created by 193 nm photolysis of HNO3 and excited to A 2Σ+ by a tunable dye laser. Time decays of fluorescence at varying pressures were measured. For O2 and H2, the quenching cross section σQ decreased with increasing N′ until N′∼10; for higher N′ it appears to remain approximately constant. Xe behaves the same way except that the decrease continues to N′=15. For Kr, σQ appears to decrease to within experimental error of zero at N′=10; and for N2 it was within error of zero above N′=10. These results have implications for laser-induced fluorescence atmospheric monitoring of OH and combustion temperature determinations, as well as a fundamental understanding of collisional quenching. Quenching of OH, N′∼1, by HNO3 was found to be 81±8 Å2.

State-to-state rate coefficients for rotational relaxation of CO in Ar

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