Photodissociation spectroscopy and dynamics of the HCCO free radical

Abstract

The photodissociation spectroscopy and dynamics of the HCCO radical have been investigated using fast radical beam photofragment translational spectroscopy. An electronic band with origin at 33 424 cm Ϫ1 has been identified. This band exhibits rotational resolution near the band origin, but the well-defined rovibronic structure is homogeneously broadened at higher photon energies. Based on the rotational structure this band is assigned to the B 2 ⌸←X 2 AЉ transition. Photofragment translational energy and angular distributions were obtained at several excitation energies. At excitation energies close to the origin, the excited, spin-forbidden CH(a 4 ⌺ Ϫ )ϩCO channel dominates, while the ground state CH(X 2 ⌸)ϩCO channel is the major channel at higher photon energies. The translational energy distributions provide evidence of competition between intersystem crossing and internal conversion dissociation mechanisms, with some evidence for nonstatistical dynamics in the CH(X 2 ⌸)ϩCO channel. This work yields an improved heat of formation for HCCO, ⌬H f ,298 0 ϭ1.83Ϯ0.03 eV.

Photodissociation spectroscopy and dynamics of CH3O and CD3O

“…Rotational resolution was not a priority in this study, and although it has been resolved, such spectra are very congested, in part due to the estimated rotational temperatures of 35-50 K in the radical beam. 52,55 Therefore, a relatively large laser step size of ≈6 cm -1 was adopted to allow increased signal averaging at each photon energy. However, because of the underlying rotational structure, each individual scan was offset slightly in energy from the previous data in a given scan range in order to average over rotational features, which might otherwise provide spurious structure since the laser step size is larger than the laser bandwidth (0.3 cm -1 ).…”

Photodissociation dynamics of the methyl radical at 212.5 nm: Effect of parent internal excitation

“…The development of pure radical sources is, therefore, clearly attractive in the study of the radical photochemistry. Pure radical sources generated using the negative ion photodetachment technique developed by Neumark et al [1][2][3] are obviously very useful for studies of radical photodissociation. In this work, we would like to report our recent experimental study on the dynamics of the CH 3 photodissociation using a pure CH 3 radical source generated by molecular beam CH 3 I photodissociation.…”

Photodissociation dynamics of the HCNN radical

“…48 HCNN and HCCO have similar ground state geometries and both have a low-lying à 2 AЈ state which forms a Renner-Teller pair with the ground state.…”

“…Osborn et al 48 carried out photodissociation experiments on HCCO, and assigned the transition excited in the those experiments to the B 2 ⌸ ← X 2 AЉ band. Because of the similarities in the photodissociation spectroscopy and dynamics of these two radicals ͑see Sec.…”

“…The molecular orbital configurations of the four lowest lying electronic states of HCCO have been described previously. 48 The ground state of HCCO has C s symmetry with the electronic configuration ...͑6aЈ͒ 2 ͑7aЈ͒ 2 ͑8aЈ͒ 2 ͑1aЉ͒ 2 ͑9aЈ͒ 2 ͑2aЉ͒ 1 . As is the case with HCNN, the two lowest electronic states are a RennerTeller pair, although in the case of HCCO the à 2 AЈ͓ 2 ⌸͔ state, with the electronic configuration ...͑6 ͒ 2 ͑7 ͒ 2 ͑1 x ͒ 2 ͑1 y ͒ 2 ͑2 x ͒ 1 ͑2 y ͒ 2 , has a linear equilibrium geometry.…”