More Like this

1. Imaging rotational energy transfer: comparative stereodynamics in CO + N 2 and CO + CO inelastic scattering

   https://doi.org/10.1039/D3CP02229C  

   Sun, Zhong-Fa ; Scheidsbach, Roy J. ; van Hemert, Marc C. ; van der Avoird, Ad ; Suits, Arthur G. ; Parker, David H. ( July 2023 , Physical Chemistry Chemical Physics)

   State-to-state rotational energy transfer in collisions of ground ro-vibrational state 13 CO molecules with N 2 molecules has been studied using the crossed molecular beam method under kinematically equivalent conditions used for 13 CO + CO rotationally inelastic scattering described in a previously published report (Sun et al. , Science , 2020, 369 , 307–309). The collisionally excited 13 CO molecule products are detected by the same (1 + 1′ + 1′′) VUV (Vacuum Ultra-Violet) resonance enhanced multiphoton ionization scheme coupled with velocity map ion imaging. We present differential cross sections and scattering angle resolved rotational angular momentum alignment moments extracted from experimentally measured 13 CO + N 2 scattering images and compare them with theoretical predictions from quasi-classical trajectories (QCT) on a newly calculated 13 CO–N 2 potential energy surface (PES). Good agreement between experiment and theory is found, which confirms the accuracy of the 13 CO–N 2 potential energy surface for the 1460 cm −1 collision energy studied by experiment. Experimental results for 13 CO + N 2 are compared with those for 13 CO + CO collisions. The angle-resolved product rotational angular momentum alignment moments for the two scattering systems are very similar, which indicates that the collision induced alignment dynamics observed for both systems are dominated by a hard-shell nature. However, compared to the 13 CO + CO measurements, the primary rainbow maximum in the DCSs for 13 CO + N 2 is peaked consistently at more backward scattering angles and the secondary maximum becomes much less obvious, implying that the 13 CO–N 2 PES is less anisotropic. In addition, a forward scattering component with high rotational excitation seen for 13 CO + CO does not appear for 13 CO–N 2 in the experiment and is not predicted by QCT theory. Some of these differences in collision dynamics behaviour can be predicted by a comparison between the properties of the PESs for the two systems. More specific behaviour is also predicted from analysis of the dependence on the relative collision geometry of 13 CO + N 2 trajectories compared to 13 CO + CO trajectories, which shows the special ‘do-si-do’ pathway invoked for 13 CO + CO is not effective for 13 CO + N 2 collisions. 

   more » « less
2. The excitation of CO in CO-dominated cometary comae

   https://doi.org/10.1093/mnras/stad268  

   Żółtowski, M. ; Lique, F. ; Loreau, J. ; Faure, A. ; Cordiner, M. ( January 2023 , Monthly Notices of the Royal Astronomical Society)

   An abundance of CO significantly surpassing the abundance of H2O is observed in the comae of comets at large heliocentric distances. In these environments, CO molecules can be the most abundant species and they may be therefore the dominant projectiles inducing collisional excitation of the cometary molecules. It is thus of high interest to investigate the excitation of CO by CO. This article provides a new set of CO–CO collisional rate coefficients for temperatures up to 150 K and for CO rotational levels j1 up to 10. These data are obtained from quantum scattering calculations using the coupled states approximation. They are used in a simple radiative transfer model in order to test their impact on the excitation of cometary CO. Because mutual (de-)excitations of the target and projectile are important, the CO projectile was assumed to be thermalized at the kinetic temperature. We found that the non-local thermodynamical equilibrium regime extends for CO densities in the range 103–107 cm−3. We also observed that as soon as the CO/H2O ratio is larger than 70 per cent/30 per cent, the contribution of H2O collisions can be neglected. Similarly, the excitation of CO by CO may be ignored for relatively low CO/H2O density ratios (≤30 per cent/70 per cent). Finally, when the coma is a ∼50 per cent/50 per cent mixture of CO and H2O, the contribution of both colliders is similar and has to be considered.

    

   more » « less
3. The effect of DNA bases permutation on surface-enhanced Raman scattering spectrum

   https://doi.org/10.1515/nanoph-2021-0021  

   Rubin, Shimon ; Nguyen, Phuong H. ; Fainman, Yeshaiahu ( March 2021 , Nanophotonics)

   null (Ed.)

   Abstract Surface-enhanced Raman scattering (SERS) process results in a tremendous increase of Raman scattering cross section of molecules adsorbed to plasmonic metals and influenced by numerous physico-chemical factors such as geometry and optical properties of the metal surface, orientation of chemisorbed molecules and chemical environment. While SERS holds promise for single molecule sensitivity and optical sensing of DNA sequences, more detailed understanding of the rich physico-chemical interplay between various factors is needed to enhance predictive power of existing and future SERS-based DNA sensing platforms. In this work, we report on experimental results indicating that SERS spectra of adsorbed single-stranded DNA (ssDNA) isomers depend on the order on which individual bases appear in the 3-base long ssDNA due to intramolecular interaction between DNA bases. Furthermore, we experimentally demonstrate that the effect holds under more general conditions when the molecules do not experience chemical enhancement due to resonant charge transfer effect and also under standard Raman scattering without electromagnetic or chemical enhancements. Our numerical simulations qualitatively support the experimental findings and indicate that base permutation results in modification of both Raman and chemically enhanced Raman spectra. 

   more » « less
4. Sentiment and structure in word co-occurrence networks on Twitter

   https://doi.org/10.1007/s41109-022-00446-2  

   Fudolig, Mikaela Irene ; Alshaabi, Thayer ; Arnold, Michael V. ; Danforth, Christopher M. ; Dodds, Peter Sheridan ( February 2022 , Applied Network Science)

   We explore the relationship between context and happiness scores in political tweets using word co-occurrence networks, where nodes in the network are the words, and the weight of an edge is the number of tweets in the corpus for which the two connected words co-occur. In particular, we consider tweets with hashtags #imwithher and #crookedhillary, both relating to Hillary Clinton’s presidential bid in 2016. We then analyze the network properties in conjunction with the word scores by comparing with null models to separate the effects of the network structure and the score distribution. Neutral words are found to be dominant and most words, regardless of polarity, tend to co-occur with neutral words. We do not observe any score homophily among positive and negative words. However, when we perform network backboning, community detection results in word groupings with meaningful narratives, and the happiness scores of the words in each group correspond to its respective theme. Thus, although we observe no clear relationship between happiness scores and co-occurrence at the node or edge level, a community-centric approach can isolate themes of competing sentiments in a corpus.

    

   more » « less
5. Collective Vibrational Strong Coupling Effects on Molecular Vibrational Relaxation and Energy Transfer: Numerical Insights via Cavity Molecular Dynamics Simulations**

   https://doi.org/10.1002/ange.202103920  

   Li, Tao E. ; Nitzan, Abraham ; Subotnik, Joseph E. ( July 2021 , Angewandte Chemie)

   For a small fraction of hot CO₂molecules immersed in a liquid‐phase CO₂thermal bath, classical cavity molecular dynamics simulations show that forming collective vibrational strong coupling (VSC) between the C=O asymmetric stretch of CO₂molecules and a cavity mode accelerates hot‐molecule relaxation. This acceleration stems from the fact that polaritons can be transiently excited during the nonequilibrium process, which facilitates intermolecular vibrational energy transfer. The VSC effects on these rates 1) resonantly depend on the cavity mode detuning, 2) cooperatively depend on Rabi splitting, and 3) collectively scale with the number of hot molecules. For larger cavity volumes, the average VSC effect per molecule can remain meaningful for up toN≈10⁴molecules forming VSC. Moreover, the transiently excited lower polariton prefers to relax by transferring its energy to the tail of the molecular energy distribution rather than distributing it equally to all thermal molecules. As far as the parameter dependence is concerned, the vibrational relaxation data presented here appear analogous to VSC catalysis in Fabry–Pérot microcavities.

    

   more » « less