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The one-laser two-color resonance enhanced multiphoton ionization REMPI [(1 + 1′) + 1] and velocity map imaging have been applied to investigate formation of molecular oxygen in excited singlet O2( a 1 Δ g ) and ground O2( X 3 Σ g - ) states in the photodissociation of van der Waals complex isoprene-oxygen C5H8-O2. These molecules were found to appear in the different rotational states with translational energy varied from a value as low as ∼1 meV to a distribution with temperature of about 940 K. The observed traces of electron recoil in the images of photoions reveal participation of several ionization pathways of the resonantly excited intermediate states of O2.

Ab initio calculations have been carried out to investigate interaction of titanium dioxide TiO 2 with oxygen O 2 in ground triplet and excited singlet states. On a singlet potential energy surface (PES) formation of a stable compound of titanium peroxide TiO 4 is revealed which should appear in reaction of TiO 2 with singlet oxygen without activation barrier. This peroxide is lower in energy than the ground state of two individual molecules TiO 2 + 3O 2 by 34.6 kcal/mol. Location of conical intersection between triplet and singlet PESs of TiO 2 O 2 is also investigated.

The strong enhancement of H-atom UV-photogeneration is revealed in van der Waals complexes of unsaturated hydrocarbons RH (RH ethylene C2H4, propylene C3H6, butadiene C4H6, butene–2 C4H8) with oxygen RH–O2 as compared with the ‘free’ RH molecules. The results obtained indicate enhancement of H atom yield to be due to one-quantum photoprocess 1RH–3O2 + hν → 3RH∗ + 3O2(1O2) providing triplet RH molecules with excitation level sufficient for dissociation.

The photogeneration of singlet oxygen O 2 ( a 1 Δ g ) resulted from the photoexcitation at 248 nm of gaseous oxygen at elevated pressure (3–80 atm) has been investigated. Singlet oxygen monitored by its IR-luminescence at 1.27 μm was found to appear via two processes which are identified to be due to absorption of individual O 2 molecules and encounter complexes O 2 –O 2 , respectively. The one-quantum absorption of complexes gives rise to appearance of oxygen in Herzberg III state O 2 ( 3 Δ u ) which is supposed to be a triplet sensitizer responsible for singlet oxygen O 2 ( a 1 Δ g ) production observed in our experiments.

Ab initio calculations at the MP2 level have been carried out for two most stable neutral isomers of van der Waals dimer (CH 3 I) 2 and for their ionized forms. It was found within MP4(SDTQ)//MP2 approach that neutral head-to-tail HT isomer (dimerization energy −778 cm −1 ) is more stable than head-to-head HH form (dimerization energy −699 cm −1 ). Comparison of calculated ionization potentials and earlier experimentally observed appearance potential of dimer ion allowed us to conclude that ionization of the more stable neutral HT form is followed by conversion into the ionic HH + form which is more stable than HT + by 0.97 eV.

Resonant two-photon ionization R2PI has been applied to the measurements of the quantum yields ϕ of iodine atoms in the fine structure states 2 P 1/2 and 2 P 3/2 arising in the UV-photodissociation process ( λ =266 and 355 nm) of the perfluoroalkyliodides C 2 F 5 I, n -C 3 F 7 I and i -C 3 F 7 I as well as of methyl iodide CH 3 I ( λ =266 nm). The measured values of the quantum yields of the excited state ( 2 P 1/2 ) of the I atoms are found to be ϕ 266 ∗ =0.921±0.010 and ϕ 355 ∗ =0.178±0.025 for C 2 F 5 I, ϕ 266 ∗ =0.919±0.011 and ϕ 355 ∗ =0.296±0.029 for n -C 3 F 7 I, ϕ 266 ∗ =0.900±0.015 and ϕ 355 ∗ =0.396±0.034 for i -C 3 F 7 I, and ϕ 266 ∗ =0.71±0.03 for CH 3 I. The results obtained show that the quantum yield ϕ 266 ∗ of the excited state atoms I( 2 P 1/2 ) in the photodissociation process of the perfluoroalkyliodides differs noticeably from unity which has previously been assumed or measured for these molecules.

Multiphoton dissociation of C 2 H 4 FCl molecules in the field of pulsed CO 2 laser radiation is discussed. It has been found that the decomposing molecules absorb approximately the same energy above the dissociation threshold ( E + = 10–15 kcal/mole) independent of the vibrational mode to take part in the first stage of excitation. The energy distribution function profile of decomposing molecules was determined through the dependent of the C 2 H 4 FCl multiphoton dissociation yield and the ratio of products on a buffer gas pressure. This distribution is an equilibrium one [Boltzmann distribution without exp (− E/kT )], truncated at the high energy limit ( E * = 75–78 kcal/mole).