Marie-Catherine Heitz

Laser control of vibrational excitation in carboxyhemoglobin: A quantum wave packet study

A coherent control algorithm is applied to obtain complex-shaped infrared laser pulses for the selective vibrational excitation of carbon monoxide at the active site of carbonmonoxyhemoglobin, modeled by the six-coordinated iron-porphyrin-imidazole-CO complex. The influence of the distal histidine is taken into account by an additional imidazole molecule. Density-functional theory is employed to calculate a multidimensional ground-state potential energy surface, and the vibrational dynamics as well as the laser interaction is described by quantum wave-packet calculations. At each instant in time, the optimal electric field is calculated and used for the subsequent quantum dynamics. The results presented show that the control scheme is applicable to complex systems and that it yields laser pulses with complex time-frequency structures, which, nevertheless, have a clear physical interpretation.

Relaxation dynamics of photoexcited calcium deposited on argon clusters: theoretical simulation of time-resolved photoelectron spectra.

Relaxation dynamics following photoexcitation of a calcium atom deposited on an icosahedral-like argon cluster Ar(n) (n approximately = 55) is investigated through theoretical simulations. Based on ab initio calculations of the CaAr molecule, a diatomics-in-molecules model is set up to efficiently describe the electronic excited states of the system. The excited state dynamics is studied using molecular dynamics with electronic transitions (Tully, J. C. J. Chem. Phys. 1990, 93, 1061). The signature of this dynamics in the time-resolved photoelectron spectra is investigated, to assess the possibility of detecting competing vibrational and electronic relaxations through pump-probe experiments. The vibrational relaxation, influenced by nonadiabatic transitions, can clearly be seen in the time-resolved photoelectron spectra. The details of the electronic relaxation, as well as the possible ejection of the chromophore, are found to be sensitive to the local environment of the calcium atom deposited on the argon cluster.

Time-resolved photoelectron spectra as probe of excited state dynamics: A full quantum study of the Na2F cluster

The excited state dynamics of the Na2F cluster initiated by a femtosecond laser pulse is studied by quantum wave packet propagation within a pump–probe setup. The probe pulse is supposed to ionize the system to yield a photoelectron spectrum that depends on the time delay between the pump- and probe pulse. It is shown that the time dependence of the photoelectron spectrum is an extremely sensitive tool to study intramolecular motion of the cluster like the energy flow between different internal modes. The potential energy surfaces involved in the photoinduced process are calculated from a pseudopotential model with repulsive and Coulomb potentials for the ions and a quantum description of the excess electron via electron-Na+ and electron-F− pseudopotentials, polarization of the ionic cores as well as electron-ion correlation being added perturbatively. The nuclear motion upon laser excitation is described by full-dimensional quantum wave packet propagation using realistic laser pulse parameters. We find t...

Theoretical study of finite-temperature spectroscopy in van der Waals clusters. I. Probing phase changes in CaArn

The photoabsorption spectra of calcium-doped argon clusters CaArn are investigated at thermal equilibrium using a variety of theoretical and numerical tools. The influence of temperature on the absorption spectra is estimated using the quantum superposition method for a variety of cluster sizes in the range 6⩽n⩽146. At the harmonic level of approximation, the absorption intensity is calculated through an extension of the Gaussian theory by Wadi and Pollak [J. Chem. Phys. 110, 11890 (1999)]. This theory is tested on simple, few-atom systems in both the classical and quantum regimes for which highly accurate Monte Carlo data can be obtained. By incorporating quantum anharmonic corrections to the partition functions and respective weights of the isomers, we show that the superposition method can correctly describe the finite-temperature spectroscopic properties of CaArn systems. The use of the absorption spectrum as a possible probe of isomerization or phase changes in the argon cluster is discussed at the l...

Methodological CASPT2 study of the valence excited states of an iron-porphyrin complex

The singlet valence excited states of an iron-porphyrin-pyrazine-carbonyl complex are investigated up to the Soret band (about 3 eV) using multi-state complete active space with perturbation at the second order (MS-CASPT2). This complex is a model for the active site of carboxy-hemoglobin/myoglobin. The spectrum of the excited states is rather dense, comprising states of different nature: d→π* transitions, d→d states, π→π* excitations of the porphyrin, and doubly excited states involving simultaneous intra-porphyrin π→π* and d→d transitions. Specific features of the MS-CASPT2 method are investigated. The effect of varying the number of roots in the state average calculation is quantified as well as the consequence of targeted modifications of the active space. The effect of inclusion of standard ionization potential-electron affinity (IPEA) shift in the perturbation treatment is also investigated.