Photodissociation of Partially Fluorinated Alkyl Iodides in Their A-Band

Tracking the conical intersection dynamics for the photoinduced Jahn-Teller switch of a Mn(iii) complex

Octahedral Mn(iii) ions predominantly exhibit an axially elongated Jahn-Teller (JT) distortion, which is responsible for their large uniaxial magnetic anisotropy. As a result, they are often used in the synthesis of single-molecule magnets (SMMs). Modulation of the JT distortion using femtosecond laser pulses could offer a route to controlling the magnetisation direction, and therefore is promising for the development of data storage devices that work on ultrafast timescales. Photoinduced switching of the distortion from an axially elongated to an axially compressed structure has been demonstrated for various Mn(iii) complexes. However, the dynamics around the region of the conical intersection for the photoinduced JT switch remains unclear. Here, ultrafast transient absorption spectra were recorded for solutions of tris(2,2,6,6-tetramethyl-3,5-heptanedionato)manganese(iii) (Mn(dpm)3) in ethanol to further explore the dynamics of the photoinduced JT switch. We observe the generation of a vibrational wavepacket on the excited state surface, which has a frequency of approximately 155 cm-1 and encompasses a JT-active vibrational mode. This coherent motion is maintained after passage through the conical intersection back to the ground state, which launches wavepackets along the ground state potential energy surface (PES) with frequencies of approximately 180 and 110 cm-1 that we assign to the elongated and compressed state, respectively. Inspection of the relative phases of the frequencies reveals phase shifts that are consistent with a one-mode reaction coordinate, and passes through the conical intersection at 1/4 and 3/4 of the excited state vibrational period. Our results provide direct insights into the non-adiabatic dynamics of Mn(iii) complexes, which can be used to guide the synthesis of optically controlled SMMs.

Productions of I, I*, and C2H5 in the A-band photodissociation of ethyl iodide in the wavelength range from 245to283nm by using ion-imaging detection

Photodissociation dynamics of ethyl iodide in the A band has been investigated at several wavelengths between 245 and 283 nm using resonance-enhanced multiphoton ionization technique combined with velocity map ion-imaging detection. The ion images of I, I(*), and C(2)H(5) fragments are analyzed to yield corresponding speed and angular distributions. Two photodissociation channels are found: I(5p (2)P(3/2))+C(2)H(5) (hotter internal states) and I(*)(5p (2)P(1/2))+C(2)H(5) (colder). In addition, a competitive ionization dissociation channel, C(2)H(5)I(+)+h nu-->C(2)H(5)+I(+), appears at the wavelengths <266 nm. The I/I(*) branching of the dissociation channels may be obtained directly from the C(2)H(5) (+) images, yielding the quantum yield of I(*) about 0.63-0.76, comparable to the case of CH(3)I. Anisotropy parameters (beta) determined for the I(*) channel remain at 1.9+/-0.1 over the wavelength range studied, indicating that the I(*) production should originate from the (3)Q(0) state. In contrast, the beta(I) values become smaller above 266 nm, comprising two components, direct excitation of (3)Q(1) and nonadiabatic transition between the (3)Q(0) and (1)Q(1) states. The curve crossing probabilities are determined to be 0.24-0.36, increasing with the wavelength. A heavier branched ethyl group does not significantly enhance the I(5p (2)P(3/2)) production from the nonadiabatic contribution, as compared to the case of CH(3)I.