Velocity map imaging studies of the photodissociation of CS₂ by two-photon excitation at around 303–315 nm

ABSTRACT

Two-photon dissociation dynamics of carbon disulfide (CS₂) have been studied by using the time-sliced velocity map ion imaging technique. Images of the S (¹D₂) and S (³P₀) photoproducts formed in the CS₂ photodissociation are acquired at four photolysis wavelengths from 303 nm to 315 nm. Vibrational states of the CS co-products are partially resolved and identified in the images. The CS (X¹Σ⁺) products are highly vibrationally excited with moderate rotational excitation. The spin–orbit state-specific dissociation dynamics are also investigated by measuring the images of three S (³P_J) spin–orbit states (J=0, 1, and 2) at photolysis wavelength 303.878 nm. The branching ratios of CS (a³Φ)/CS (X¹Σ_g⁺) are determined to be 0.05 ± 0.02, 0.17 ± 0.04, and 0.26 ± 0.05 for the three spin–orbit states S (³P₀), S (³P₁), and S (³P₂) respectively, implying a strong spin–orbit coupling exists in the dissociation process. The averaged anisotropy parameters β₂>0 and β₄∼0 suggest that the CS₂ molecules undergo a sequential transition 2¹B₂(2¹Σ⁺)←1¹B₂(¹Δ_u)←X¹Σ_g⁺ with the intermediate state 1¹B₂ having a long lifetime, followed by nonadiabatic and spin–orbit couplings to other electronic states and then dissociate.

GRAPHICAL ABSTRACT

KEYWORDS:

• Photodissociation
• velocity map ion imaging
• two-photon excitation

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The experimental work is supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (grant number XDB17000000), the Chemical Dynamics Research Center (grant number 21688102), the National Natural Science Foundation of China (NSFC Nos. 21873099, 21922306), the Key Technology Team of the Chinese Academy of Sciences (grant number GJJSTD20190002), and the international partnership program of Chinese Academy of Sciences (No. 121421KYSB20170012).