Selective bond breaking of CO₂ in phase-locked two-color intense laser fields: Laser field intensity dependence

Selective bond breaking of CO₂ in phase-locked ω-2ω two-color intense laser fields (λ = 800 nm and 400 nm, total field intensity I ∼ 10¹⁴ W cm^-2) has been investigated by coincidence momentum imaging. The CO⁺ and O⁺ fragment ions produced by two-body Coulomb explosion, CO₂²⁺ → CO⁺ + O⁺, exhibit asymmetric distributions along the laser polarization direction, showing that one of the two equivalent C-O bonds is selectively broken by the laser fields. At a field intensity higher than 2 × 10¹⁴ W cm^-2, the largest fragment asymmetry is observed when the relative phase between the ω and 2ω laser fields is ∼0 and π. On the other hand, an increase of the asymmetry and a shift of the phase providing the largest asymmetry are observed at lower field intensities. The selective bond breaking and its dependence on the laser field intensity are discussed in terms of a mechanism involving deformation of the potential energy surfaces and electron recollision in intense laser fields.