Ultrafast Dynamics of the SO₂(H₂O)_n Cluster System

Abstract

An investigation of the excited-state dynamics of SO2(H2O)n (n = 1-5) clusters following excitation by ultrafast laser pulses to 4.7 eV (coupled 1A2 and 1B1 states) and 9.3 eV (F band) is presented. The findings for the coupled 1A2 and 1B1 states are in good agreement with published computational work and indicate the division of the initial excited-state population into the double well produced by the coupled states. A photoinduced ion-pair formation process is proposed as a likely source of the observed dynamic behavior following the 9.3 eV excitation. Energetics calculations are also presented that support the ion-pair mechanism. A lack of cluster size dependence in the measured time constants indicate surface solvation of SO2 rather than a cluster structure with the SO2 molecule fully encompassed by water molecules.

Single photon ionization of van der Waals clusters with a soft x-ray laser: (SO2)n and (SO2)n(H2O)m

“…12,13,21 Nonetheless, results presented in the present work ͑Fig. 6͒ lead to the conclusion that ͑H 2 O͒ n−1 H + arise from ͑H 2 O͒ n neutrals.…”

“…Femtosecond ionization spectra show that the ͑SO 2 ͒H + ion is detected from the ionization of the mixed neutral dimer ͑SO 2 ͒͑H 2 O͒. 12,13,21 In the present experiment with 26.5 eV ionization, obvious signals of the unprotonated mixed dimer ion ͑SO 2 ͒ ϫ͑H 2 O͒ + ͑Fig. 5͒ and mixed ͑SO 2 ͒ n ͑H 2 O͒ + ions ͑1 ഛ n ഛ 5͒ ͑Fig.…”

“…10,11 Mixed sulfur dioxide/water clusters have also been studied with multiphoton femtosecond ionization reflectron time of flight mass spectroscopy ͑TOFMS͒. 12,13 The measured times for dissociation are independent of cluster size, indicating that the ions formed are all at the cluster surface rather than "solvated" by the other, neutral members of the cluster. SO 2 molecules are thus more likely to be weakly absorbed rather than solvated in a low water environment.…”

Electronic relaxation dynamics in large anionic water clusters: (H2O)n− and (D2O)n− (n=25–200)

“…The time-dependent integrated intensity of feature B for each cluster is fit to the convolution of an exponential decay/ recovery function and a Gaussian function accounting for the experimental response. 71 Prior to convolution, the exponential decay function has the form…”

Hydration increases the lifetime of HSO<sub>5</sub> and enhances its ability to act as a nucleation precursor – a computational study

“…(The hydrates of O 2 were not studied, as they are likely to be extremely weakly bound due to the nonpolarity of the O 2 molecule. Also, only the monohydrate of SO 2 was considered, as experimental evidence (Dermota et al, 2005) indicates that SO 2 in water clusters only interacts with one water molecule). Free energies have been computed using the G3B3 combination method (Baboul et al, 1999) which involves B3LYP/6-31G(d) geometry optimizations and frequency calculations (using a scaling factor of 0.96) together with a series of higher-level (MP2(full), MP4 and QCSID(T)) single-point energy calculations and empirical corrections.…”