Photolysis Production and Spectroscopic Investigation of the Highest Vibrational States in H2 (X1Σg+ v = 13, 14)

Color-Tunable, Excitation-Dependent, and Water Stimulus-Responsive Room-Temperature Phosphorescence Cellulose for Versatile Applications

Smart-response materials with ultralong room-temperature phosphorescence (RTP) are highly desirable, but they have rarely been described, especially those originating from sustainable polymers. Herein, a variety of cellulose derivatives with 1,4-dihydropyridine (DHP) rings are synthesized through the Hantzsch reaction, giving impressive RTP with a long lifetime of up to 1251 ms. Specifically, the introduction of acetoacetyl groups and DHP rings promotes the spin-orbit coupling and intersystem crossing process; and multiple interactions between cellulose induce clustering and inhibit the nonradiative transitions, boosting long-live RTP. Furthermore, the resulting transparent and flexible cellulose films also exhibit excitation-dependent and color-tunable afterglows by introducing different extended aromatic groups. More interestingly, the RTP performance of these films is sensitive to water and can be repeated in response to wet/dry stimuli. Inspired by these advantages, the RTP cellulose demonstrates advanced applications in information encryption and anti-counterfeiting. This work not only enriches the photophysical properties of cellulose but also provides a versatile platform for the development of sustainable afterglows.

The vibronic state dependent predissociation of H2S: determination of all fragmentation processes

Photochemistry plays a significant role in shaping the chemical reaction network in the solar nebula and interstellar clouds. However, even in a simple triatomic molecule photodissociation, determination of all fragmentation processes is yet to be achieved. In this work, we present a comprehensive study of the photochemistry of H2S, derived from cutting-edge translational spectroscopy measurements of the H, S(1D) and S(1S) atom products formed by photolysis at wavelengths across the range 155-120 nm. The results provide detailed insights into the energy disposal in the SH(X), SH(A) and H2 co-fragments, and the atomisation routes leading to two H atoms along with S(3P) and S(1D) atoms. Theoretical calculations allow the dynamics of all fragmentation processes, especially the bimodal internal energy distributions in the diatomic products, to be rationalised in terms of non-adiabatic transitions between potential energy surfaces of both 1A' and 1A'' symmetry. The comprehensive picture of the wavelength-dependent (or vibronic state-dependent) photofragmentation behaviour of H2S will serve as a text-book example illustrating the importance of non-Born-Oppenheimer effects in molecular photochemistry, and the findings should be incorporated in future astrochemical modelling.

Photodissociation of H2S: A New Pathway for the Production of Vibrationally Excited Molecular Hydrogen in the Interstellar Medium

Hydrogen sulfide (H₂S) is the most abundant S-bearing molecule in the solar nebula. Although its photochemistry has been studied for decades, the H₂ fragment channel is still not well-understood. Herein, we describe the photodissociation dynamics of H₂S + hv → S(¹S) + H₂(X¹Σ_g⁺) with the excitation wavelength of 122 nm ≤ λ ≤ 136 nm. The results reveal that the H₂(X) fragments formed are significantly vibrationally excited, with the quantum yields of ∼87% of H₂(X) fragments populated in vibrational levels v″ = 3, 4, 5, and 6. Theoretical analysis suggest that these H₂ products are formed on the H₂S 4¹A' state surface following a nonadiabatic transition via an avoided crossing from the 3¹A' to 4¹A' state. The estimated quantum yield of the S(¹S) + H₂ channel is ∼0.05, implying this channel should be incorporated into the appropriate interstellar chemistry models.

Shape Resonances in H_{2} as Photolysis Reaction Intermediates

Shape resonances in H_{2}, produced as reaction intermediates in the photolysis of H_{2}S precursor molecules, are measured in a half-collision approach. Before disintegrating into two ground state H atoms, the reaction is quenched by two-photon Doppler-free excitation to the F electronically excited state of H_{2}. For J=13, 15, 17, 19, and 21, resonances with lifetimes in the range of nano- to milliseconds were observed with an accuracy of 30 MHz (1.4 mK). The experimental resonance positions are found to be in excellent agreement with theoretical predictions when nonadiabatic and quantum electrodynamical corrections are included. This is the first time such effects are observed in collisions between neutral atoms. From the potential energy curve of the H_{2} molecule, now tested at high accuracy over a wide range of internuclear separations, the s-wave scattering length for singlet H(1s)+H(1s) scattering is determined at a=0.2735_{31}^{39} a_{0}.

Rotational and nuclear-spin level dependent photodissociation dynamics of H2S

The detailed features of molecular photochemistry are key to understanding chemical processes enabled by non-adiabatic transitions between potential energy surfaces. But even in a small molecule like hydrogen sulphide (H₂S), the influence of non-adiabatic transitions is not yet well understood. Here we report high resolution translational spectroscopy measurements of the H and S(¹D) photoproducts formed following excitation of H₂S to selected quantum levels of a Rydberg state with ¹B₁ electronic symmetry at wavelengths λ ~ 139.1 nm, revealing rich photofragmentation dynamics. Analysis reveals formation of SH(X), SH(A), S(³P) and H₂ co-fragments, and in the diatomic products, inverted internal state population distributions. These nuclear dynamics are rationalised in terms of vibronic and rotational dependent predissociations, with relative probabilities depending on the parent quantum level. The study suggests likely formation routes for the S atoms attributed to solar photolysis of H₂S in the coma of comets like C/1995 O1 and C/2014 Q2.

The photodissociation dynamics of small molecules in the vacuum ultraviolet range can have key implications for astrochemical modelling, but revealing such dynamical details is a challenging task. Here the authors, combining high resolution experimental techniques, provide a detailed description of the fragmentation dynamics of selected rotational levels of a predissociated Rydberg state of H₂S.