Photodissociation dynamics of carbonyl chloride fluoride and its implications for phosgene three body decay

Abstract

The photodissociation dynamics of COFCl has been studied by monitoring Cl fragments by resonance enhanced multi-photon ionisation and time-of-Ñight techniques at dissociation wavelengths near 235 nm. The COFCl heat of formation and the dissociation energy for CwCl bond Ðssion were for the Ðrst time experimentally determined :(COFCl) \ [397 ^15 kJ mol~1 and kJ mol~1.of the available energy is channelled into FCO rotation and bending vibration. The remaining energy is released as product translation. Other than in phosgene, no spinÈorbit state selective behaviour is observed. The observations agree with a decay mechanism within the COFCl molecular plane as well as with a fragmentation via out-of-plane movement of the departing Cl atom. The structural and electronic similarity of COFCl and allows conclusions to be drawn on the dissociation. The Ðndings are evidence for a COCl 2 COCl 2 previously proposed decay mechanism for the asynchronous concerted three body decay of phosgene into CO ] 2Cl. The Ðrst bond cleavage produces ground and excited spinÈorbit state Cl and Cl*, respectively, with large kinetic energy release, while breaking the second CwCl bond exclusively generates slow ground state Cl atoms.

Theoretical study of structures of the X2CO and XYCO molecules (X and Y = H, F, or Cl) in the ground and lowest excited triplet electronic states

“…Deviations of the geometric parameters (a) of the H 2 CO molecule in the S 0 (1, 2) and T 1(3,4) states and the energy parameters (b), viz., the inversion barriers(1,2) and the energies of the electronic transition T 1 ←S 0(3,4), calculated by the MP2(1, 3)and B3LYP (2, 4) methods with different AO basis sets from the corresponding experimental values; see Eqs…”

Predissociative T1and S1states of carbonyl chlorofluoride (ClFCO) and their photodissociation pathways

“…Section 3.2 analyses our results for the geometries and vibrational properties of the T 1 and S 1 states, for which reliable previous results are limited. The PESs for the three bond dissociation paths are presented in Section 3.3 followed by Section 3.4 for a discussion of the implications of our results with respect to previous photodissociation dynamics experiments [12,21,22].…”

“…It is interesting to note that the electronic absorption spectrum of ClFCO was reported about four decades ago [3], but no theoretical discussion has followed, and these results have never been explicitly used in the analyses of subsequent experimental results [12,21,22]. The experimental value for the ATE of S 1 is 4.79 eV [3], and the experimentally suggested vibration frequencies are 754, 553, 360, and 307 cm À1 ; these values are in good agreement with our calculated values, 4.70-4.78 eV and 716, 583, 379, and 314 cm À1 , respectively, as shown in Table 3.…”

“…Even our recent theoretical studies of the low-lying excited states of tetra-atomic halocarbonyls X 2 CY (X ¼ F, Cl; Y ¼ O, S) [24] and ClFCS [25] did not include ClFCO. The lack of reliable theoretical information on the excited electronic states of ClFCO means that previous experimental studies [12,21,22] of the photodissociation of ClFCO have been analysed only phenomenally, and that very few details of its ultrafast dynamics have emerged. This lack is probably one of the reasons why detailed experimental and theoretical studies have not so far been conducted, in spite of the unique and interesting features of this molecule.…”

“…The interest in ClFCO also stems from the fact that it is one of the specific cases encountered in the investigation of three-body decay dynamics [11][12][13], a new area in the study of ultrafast photodynamic processes. The two different halogen elements, F and Cl, in the same molecule introduce additional variety, therefore ClFCO has subtle features that are useful in the study and the artificial control of ultrafast processes with mechanisms ranging from synchronous to sequential [13,14].…”