Study on the Second Dissociation Channel of CS2+ by Using [1+1] Two-Photon Dissociation

The second dissociation channel (CS 2 + → CS + ( X 2 Σ) + S( 3 P)) of CS 2 + molecular ions has been investigated by measuring the photofragment CS + excitation (PHOFEX) spectrum in the wavelength range of 385−435 nm, where the CS 2 + molecular ions were prepared purely by [3 + 1] multiphoton ionization of the neutral CS 2 molecules at 483.2 nm. The CS + PHOFEX spectrum was assigned essentially to the CS 2 + ( à 2 Π u ) ← CS 2 + ( X̃ 2 Π g ) transition, such as the S + PHOFEX spectrum, which has been obtained previously. The product branching ratios (CS + /S + ), as measured from the PHOFEX spectra, increase from 0 to slightly larger than 1 in the wavenumber range of 47200−50400 cm -1 . The adiabatic appearance potential of the CS + ion was determined to be 5.852 ± 0.005 eV above the X̃ 2 Π g,3/2 (0,0,0) level of CS 2 + from the appearance wavenumber of 47196.2 cm -1 to produce the CS + ion. The dissociation mechanism to get to CS + + S from CS 2 + was discussed and preliminarily attributed to (i) CS 2 + ( X̃ 2 Π g ) → CS 2 + (à 2 Π u ) through one-photon excitation, (ii) CS 2 + ( à 2 Π u ) → CS 2 + ( X̃ † ) via internal conversion process due to the vibronic coupling between the à and X̃ states, (iii) CS 2 + ( X̃ † ) → CS 2 + ( B̃ 2 Σ u + ) through the second photon excitation, and (iv) CS 2 + ( B̃ 2 Σ u + ) → CS + ( X 2 Σ) + S( 3 P), because of the potential curve crossing with the repulsive 4 Σ - state and/or the 2 Σ - state correlated with the second dissociation limit.