Femtosecond time-resolved mass and photoelectron spectroscopic study of OC1O photodissociation. Coherent energy transfer in a stepwise reaction

Femtosecond pump–probe photodissociation of OClO: direct observation of the 2A1 state and the role of accidental multiphoton resonance

“…The present work demonstrates that a direct observation of the 2 A 1 state is practical with a proper pulse, confirming the tentative conclusion of Stert et al [10]. We further suggest that the observed distinct photodissociation dynamics of the 2 A 2 state using pulses of slightly different wavelengths [8][9][10] results from a time-delayed accidental resonance of the probe pulses with highly excited D or E states, rather than changes in the dynamics in the 2 A 2 state itself. This also explains the 'abnormal' transient peak which Blackwell et al [9] found in the OClO þ ion signal after excitation of OClO with a strong laser pulse.…”

“…In this Letter we report a consistent picture for the pump-probe experiments of BLC and SRNR on the OClO molecule [8][9][10]. The present work demonstrates that a direct observation of the 2 A 1 state is practical with a proper pulse, confirming the tentative conclusion of Stert et al [10].…”

“…The OClO molecule has been studied with the realtime pump-probe technique by several groups [7][8][9][10]. Baumert et al [7] have investigated the dynamics of the OClO molecule with 140 fs laser pulses in the energy range from 3.52 (352 nm) to 4.03 eV (308 nm) and found that the OClO molecule decays with a double-exponential behavior.…”

“…A fast decay of a few tens of femtoseconds was attributed to direct dissociation on the 2 A 2 surface and a slower decay, in 300-500 fs, to an indirect channel through non-adiabatic coupling with neighboring electronic states. Blackwell et al (BLC) [8,9] used pump laser pulses at 3.21 eV (386 nm) and probe pulses at 4.82 eV (257 nm) to study the dynamics of the OClO molecule. They found a time constant of 4.6 ps for the initial decay from the 2 A 2 state to an intermediate state, followed by a decay process with a time constant of 0.25 ps.…”

“…Therefore, the observed mass spectra are expected to be similar. However, a substantial difference between them has been observed [8,10] but the underlying mechanism has not been investigated.…”