Tony Hansson

Femtosecond laser spectroscopy on the vibrational wave packet dynamics of the A1Σ+ state of NaK

Abstract The vibrational wave packet dynamics of a heteronuclear diatomic alkali molecule in an excited state, the A 1 Σ + state of gaseous NaK, has been measured for the first time. At λ pump = 790 nm, a wave packet oscillation period of 442 fs and dephasing within 10 ps has been observed. This dynamics has been analysed by calculation of Franck-Condon factors and difference potentials. It is from this seen that initially the pump pulse prepares a wave packet at the inner turning point of the A-state. The wave packet then evolves in time and is probed at the outer turning point by a transition to the E-state with subsequent fluorescence detection.

Wavepacket dynamics and predissociation of the state of Rb2

Abstract We present the first experimental investigation of the real-time dynamics of predissociation in a diatomic molecule involving more than two electronic states – the predissociation of the D 1 Π u state of Rb2. Our results show that the state is strongly predissociated, τ≈5 ps, above a sharp energy threshold. We propose that mainly the (1) 3 Δ u state causes the fast predissociation and that the fine-structure components of the products are mixed by coupling among molecular states at large internuclear distances. Furthermore, an outward–inward asymmetry of the wavepacket signal is attributed to autoionisation of the wavepacket evolving in the probe (Rydberg) state.

Ultrafast multiphoton ionization dynamics and control of NaK molecules

The multiphoton ionization dynamics of NaK molecules is investigated experimentally using one-color pump-probe femtosecond spectroscopy at 795 nm and intermediate laser field strengths (about 10 GW ...

Time-resolved measurements of the B2Σ state of SrF by laser spectroscopy

Abstract We report a time-resolved investigation of the low-lying state, B 2 Σ , of gaseous SrF using laser spectroscopy with the following derived zero-pressure lifetime τ (B 2 Σ ( ν ′=0))=25.4±0.8 ns. Such measurements constitute an important contribution to our overall understanding of excited alkaline earth halides. They are also applied to the interpretation of molecular dynamic investigations of halogen atomic abstraction reactions by excited atoms, in the present case, Sr [5 s 5 p ( 3 P J )] , with molecules such as CH 3 F where the A → X and B → X chemiluminescence emissions are employed in the time-domain to monitor the production of electronically excited SrF on collision.

Vibrational wave packet dynamics in NaK : The A (1)Sigma(+) state

A combined experimental and theoretical study of the vibrational wave packet dynamics for the NaK molecule in the A (1)Sigma(+) state is presented. The experiment utilises a 790 nm one-colour fem ...

Rydberg state-mediated photoionisation of dissociating NaK wave packets in the B1Π state

Abstract The photoionisation dynamics of NaK molecules in the B 1 Π state is studied in both frequency and time domain by femtosecond laser spectroscopy. Comparison to model calculations shows that the photoionisation proceeds via intermediate-to-high- n Rydberg states. These Rydberg states act as Franck–Condon windows in the time-dependent experiment, and the molecular ions produced by autoionisation of the Rydberg states are shown to reflect the wave packet evolution in the B state. Consequently, Rydberg state-mediated photoionisation is proposed as a viable method for probing molecular wave packet dynamics.

Collisionally promoted near-infrared excitation of green triplet emission in NaK molecules

A collisionally promoted green emission band appearing in mixed sodium-potassium vapour is observed when the vapour is irradiated with a broadband continuous-wave laser at wavelengths around 780 nm. Previously not reported bound-bound transitions from the 3 and 5 + states down to a + in NaK molecules are found to be the origin of the emission. By fitting contributions from the individual vibrational states to the shape of the fluorescence band the Te for 5 + and 3 are estimated as 24 770 and 24 630 cm-1, respectively. Calculations of two-photon excitation spectra, resonantly enhanced by the A + state, show that the triplet manifold can be accessed from the 3 state after collisional vibrational redistribution to reach gateway levels perturbed by 5 +. Additional collisional redistribution transfers a fraction of this population to the 3 state. This seems to be the first time a collisionally promoted all-molecular one-colour scheme to excite triplet emission in heteronuclear alkali diatomic molecules with wavelengths shorter than that of the excitation light is reported and extensively analysed, a process of potential interest in the construction of new laser types.

A classical phase r-centroid approach to molecular wave packet dynamics – illustrating the danger of using an incomplete set of initial states for thermal averaging

Abstract An inexpensive semiclassical method to simulate time-resolved pump–probe spectroscopy on molecular wave packets is applied to NaK molecules at high temperature. The method builds on the introduction of classical phase factors related to the r -centroids for vibronic transitions and assumes instantaneous laser–molecule interaction. All observed quantum mechanical features are reproduced – for short times where experimental data are available even quantitatively. Furthermore, it is shown that fully quantum dynamical molecular wave packet calculations on molecules at elevated temperatures, which do not include all rovibrational states, must be regarded with caution, as they easily might yield even qualitatively incorrect results.