Photodissociation spectroscopy and dissociation dynamics of TiO(+)(CO(2)).
TiO(+)(CO(2)) is produced by reaction of laser-ablated titanium atoms with CO(2) and subsequent clustering, supersonically cooled, and its electronic spectroscopy was characterized by photofragment spectroscopy, monitoring loss of CO(2). The photodissociation spectrum consists of a vibrationally resolved band in the visible, with extensive progressions in the covalent Ti-O stretch (952 cm(-1) vibrational frequency and 5 cm(-1) anharmonicity) and in the TiO(+)-CO(2) stretch (186 cm(-1)) and rock (45 cm(-1)). The band origin is at 13 918 cm(-1), assigned using titanium isotope shifts, and the spectrum extends to 17 350 cm(-1). The excited-state lifetime decreases dramatically with increasing internal energy, from 1100 ns for the lowest energy band (v'(TiO) = 0) to <50 ns for v'(TiO) = 3. The long photodissociation lifetime substantially reduces the photodissociation quantum yield at low energy, likely due to competition with fluorescence. The fluorescence rate is calculated to be k(fl) = 7.5 x 10(5) s(-1), based on the measured excited-state lifetimes and relative band intensities. This corresponds to an integrated oscillator strength of f = 0.0056. Electronic structure calculations help to assign the spectrum of TiO(+)(CO(2)) and predict allowed electronic transitions of TiO(+) in the visible, which have not been previously measured. Time-dependent density functional calculations predict that the observed transition is due to B, (2)Pi <-- X, (2)Delta in the TiO(+) chromophore and that binding to CO(2) red shifts the TiO(+) transition by 1508 cm(-1) and lowers the Ti-O stretch frequency by 16 cm(-1). Combining the computational and experimental results, the (2)Pi state of TiO(+) is predicted to lie at T(0) = 15 426 +/- 200 cm(-1), with frequency omega(e) = 968 +/- 5 cm(-1) and anharmonicity omega(e)x(e) = 5 cm(-1). The calculations also predict that there is only one low-lying (2)Sigma state of TiO(+), contrary to conclusions derived from photoelectron spectroscopy of TiO. Prospects for astronomical observation of TiO(+) via the (2)Pi-(2)Delta transition are also discussed.
Department of Chemistry, University of Massachusetts Amherst, Amherst, Massachusetts 01003, USA.
K Manori
KM
Perera
Ricardo B
RB
Metz