A combined experimental and theoretical study of resonance emission spectra of SO2(C̃ )

Ro-vibronic transition intensities for triatomic molecules from the exact kinetic energy operator; electronic spectrum for the C̃ 1B2 ← X̃ 1A1 transition in SO2

A procedure for calculating ro-vibronic transition intensities for triatomic molecules within the Born-Oppenheimer approximation is reported. Ro-vibrational energy levels and wavefunctions are obtained with the DVR3D suite, which solves the nuclear motion problem with an exact kinetic energy operator. Absolute transition intensities are calculated both with the Franck-Condon approximation and with a full transition dipole moment surface. The theoretical scheme is tested on C̃ ¹B₂ ← X̃ ¹A₁ ro-vibronic transitions of SO₂. Ab initio potential energy and dipole moment surfaces are generated for this purpose. The calculated ro-vibronic transition intensities and cross sections are compared with the available experimental and theoretical data.

Final State Resolved Quantum Predissociation Dynamics of SO2(C̃1B2) and Its Isotopomers via a Crossing with a Singlet Repulsive State

The fragmentation dynamics of predissociative SO₂(C̃¹B₂) is investigated on an accurate adiabatic potential energy surface (PES) determined from high level ab initio data. This singlet PES features non-C_2v equilibrium geometries for SO₂, which are separated from the SO(X̃³Σ^-) + O(³P) dissociation limit by a barrier resulting from a conical intersection with a repulsive singlet state. The ro-vibrational state distribution of the SO fragment is determined quantum mechanically for many predissociative states of several sulfur isotopomers of SO₂. Significant rotational and vibrational excitations are found in the SO fragment. It is shown that these fragment internal state distributions are strongly dependent on the predissociative vibronic states, and the excitation typically increases with the photon energy.

First-principles C band absorption spectra of SO2 and its isotopologues

The low-energy wing of the C∼B21←X∼¹A₁ absorption spectra for SO₂ in the ultraviolet region is computed for the 32S,³³S,³⁴S and ³⁶S isotopes, using the recently developed ab initio potential energy surfaces (PESs) of the two electronic states and the corresponding transition dipole surface. The state-resolved absorption spectra from various ro-vibrational states of SO₂(X∼¹A₁) are computed. When contributions of these excited ro-vibrational states are included, the thermally averaged spectra are broadened but maintain their key characters. Excellent agreement with experimental absorption spectra is found, validating the accuracy of the PESs. The isotope shifts of the absorption peaks are found to increase linearly with energy, in good agreement with experiment.

CALCULATION OF TRANSITION AMPLITUDES WITH A SINGLE LANCZOS PROPAGATION

We review in this article a recently proposed energy-global method that is capable of calculating the entire transition amplitude matrix with a single Lanczos propagation. This method requires neither explicit computation nor storage of the eigenfunctions, rendering it extremely memory efficient. Procedures are proposed to handle situations where "spurious" eigenvalues aggregate around true eigenvalues due to round-off errors. This method is amenable to both real-symmetric and complex-symmetric Hamiltonians. Applications to molecular spectra and reactive scattering are presented. Its relationships with other methods are also discussed.

Emission spectrum and relaxation kinetics of SO2 induced by 266 nm laser

Laser induced fluorescence (LIF) emission spectrum of SO(2) in the range of 270.0-470.0 nm has been obtained with the quadruple harmonic output (266 nm) of a pulsed Nd:YAG laser as excitation source. The spectrum is composed of a continuous envelope in the short wavelength side, while it shows the character of banded structure superimposed on a continuous one in the long wavelength region. Fluorescence emission from the hybrid states of A(1)A(2)+B(1)B(1) and X(1)A(1)+B(1)B(1) forms the continuous envelope and phosphorescence emission from the triplet state a(3)B(1) forms the banded progression. It is also found that direct emission from laser excited states is very weak. The primary portion of the emission is from the energy levels populated by collision relaxation or collision induced intersystem crossing process. The harmonic frequencies and inharmonic coefficients of the symmetric stretching vibration and the bending vibration of X(1)A(1) state are derived from the ascription of the phosphorescence progression.

Theoretical studies of absorption cross sections for the C (1)B(2)-X (1)A(1) system of sulfur dioxide and isotope effects

The C (1)B(2)-X (1)A(1) photoexcitation of SO(2) was studied to investigate excited-state dynamics and the effects of the initial vibrational state. Ultraviolet photoabsorption cross sections (sigma's) of seven isotopologues ((32)S (16)O(2), (33)S (16)O(2), (34)S (16)O(2), (36)S (16)O(2), (32)S(16)O(17)O, (32)S(16)O(18)O, (34)S(16)O(18)O) were computed using the wave packet propagation technique based on the three-dimensional potential energy surfaces of the X and C states, which were calculated using the ab initio molecular orbital configuration interaction method. Numerous wave packet simulations were carried out under the adiabatic approximation and used to calculate the sigma's of the seven isotopologues at 298 K; we concluded that the absorption spectrum of SO(2) can be reliably modeled within the adiabatic framework based on the analysis of the time evolution of the wave packet. The calculated sigma's are in reasonable agreement with the recent experiment in the 190-228 nm region, and the isotope shifts of the peaks for (33)S (16)O(2) and (34)S (16)O(2) relative to the corresponding peaks for (32)S (16)O(2) are in good agreement with the observed data. Relative to the sigma of (32)S (16)O(2), isotopic substitution shows a significant increment for those of (34)S (16)O(2) and (36)S (16)O(2) in the 190-228 nm region. This trend is consistent with the observed data.