Marcia T. Portella-Oberli

Femtosecond dynamics of electronic 'bubbles' in solid argon: viewing the inertial response and the bath coherences

The dynamics of non-polar electronic solvation has been studied on a model system consisting of NO-doped solid Ar. Excitation of the lowest Rydberg state A(3ss) of NO leads to formation of an electronic bubble, which has been studied by femtosecond pump-probe spectroscopy and classical Mol. Dynamics simulations. The early time behavior of the transients is identified as the inertial component of the medium response. This first response is followed by a recurrent low-frequency oscillatory motion of the cage for up to .apprx.2 ps, indicative of coherence in the bath modes. [on SciFinder (R)]

Femtosecond transition state spectroscopy of solids: electronic ‘bubble’ formation in solid hydrogen

We report the femtosecond nuclear dynamics of an electronic ‘bubble’ in solid H2. The bubble formation results from the impulsive excitation of the lowest Rydberg state A2Σ+ (3sσ) of the NO impurity by a UV femtosecond pulse. The evolution of the bubble was followed in real-time by means of a probe pulse which maps the transient configurations by inducing transitions to higher-lying Rydberg states. It is found that the bubble is formed coherently by the collective displacement of the matrix species, without recurrences (coherent or incoherent) of the cage motion. The bubble reaches its final configuration in ∼ 1.5 ps.

Ultrafast dynamics of Rydberg states in the condensed phase

The ultrafast dynamics are reported of bubble formation following excitation of the A 2S+ 3ss(v = 0) Rydberg state of NO trapped in Ar matrixes. The study is carried out by a fs pump-probe technique. The detected signal is the depletion of Rydberg fluorescence induced by Rydberg-Rydberg transitions. Possibly the bubble is formed on a timescale of a few ps. [on SciFinder (R)]

Ultrafast intramolecular relaxation of C60

Transient absorption spectra of C60 mols. trapped in cryogenic rare gas matrixes and dissolved in room temp. toluene were measured with a time resoln. of 90 fs. An absorption build-up with a characteristic rise time of 200 fs is measured, which is solvent-, temp.- and probe wavelength-independent. It is attributed to the population of an intermediate state by the decay of the initially excited singlet state(s) by vibrational and electronic relaxation. The data are discussed in the light of results from the literature and a general picture of intramol. relaxation in C60 is proposed. [on SciFinder (R)]

Picosecond and femtosecond studies of the energy redistribution in matrix-isolated C60 molecules

The intramol. energy relaxation processes of UV-excited C60 mols. embedded in Ar crystals were studied by picosecond fluorescence studies and femtosecond pump-probe absorption spectroscopy. The various internal energy relaxation steps are clearly identified. The importance of intramol. energy relaxation processes in solid C60 films is underlined. [on SciFinder (R)]

Dynamics of electronic “bubble” formation in solid hydrogen

Excitation of the A(3ss) Rydberg state of NO trapped in an H2 crystal leads to the electronic bubble formation around the NO impurity, resulting in an increase of 0.9 .ANG. of the ground state cage radius. Its dynamics was followed in real-time by femtosecond pump-probe spectroscopy. Bubble formation is completed in .apprx.1.5 ps without recurrences of the cage motion. A model based on classical hydrodynamics provides quant. agreement with exptl. data, suggesting that solid H can be described like a liq. on ultrashort time scales. [on SciFinder (R)]

Femtosecond study of the rise and decay of carbenes in solution

Abstract The ultrafast production and decay of carbenes from the diphenyldiazomethane precursor in isooctane has been investigated by femtosecond transient absorption spectroscopy. Diphenylcarbene is produced in less than 300 fs in a singlet state. It then undergoes an ultrafast (∼300 fs) internal conversion followed by an intermediate step of a few picoseconds, which we attribute to a conformational change between its C 1 and C 2v geometries. Finally, intersystem crossing from S 1 to the triplet ground state occurs in ∼100 ps.

Electronic “Bubble” Dynamics in Solid Argon

We follow the ultrafast dynamics of the medium response to impulsive Rydberg state excitation of an NO molecule trapped in solid argon using a femtosecond fluorescence depletion pump-probe technique. Our results show that the cage expands by undergoing collective coherent recurrencies for over ∼3 ps, on its way to the fully relaxed electronic “bubble” conformation.

“Bubble” Dynamics Following Rydberg State Excitation in Rare Gas Matrices

The bubble build-up following Rydberg state excitation in rare gas matrixes was modeled on a system comprising NO mols. trapped in Ar matrixes. The bubble formation was probed in real time using the time-resolved fluorescence depletion technique. The NO mols. were excited to their A2S+/3ss(v=0) state. Following excitation, the cage reached its equil. configuration on a timescale of 3.8-4.5 ps, depending on the excitation energy. [on SciFinder (R)]