Sumana Raj

All Publications

• Site-specific electronic structure of covalently linked bimetallic dyads from nitrogen K-edge x-ray absorption spectroscopy. The Journal of chemical physics Ryland, E. S., Liu, X., Kumar, G., Raj, S. L., Xie, Z. L., Mengele, A. K., Fauth, S. S., Siewerth, K., Dietzek-Ivanšić, B., Rau, S., Mulfort, K. L., Li, X., Cordones, A. A. 2024; 160 (8)

  Abstract

  A nitrogen K-edge x-ray absorption near-edge structure (XANES) survey is presented for tetrapyrido[3,2-a:2',3'-c:3″,2″-h:2‴,3‴-j]phenazine (tpphz)-bridged bimetallic assemblies that couple chromophore and catalyst transition metal complexes for light driven catalysis, as well as their individual molecular constituents. We demonstrate the high N site sensitivity of the N pre-edge XANES features, which are energetically well-separated for the phenazine bridge N atoms and for the individual metal-bound N atoms of the inner coordination sphere ligands. By comparison with the time-dependent density functional theory calculated spectra, we determine the origins of these distinguishable spectral features. We find that metal coordination generates large shifts toward higher energy for the metal-bound N atoms, with increasing shift for 3d < 4d < 5d metal bonding. This is attributed to increasing ligand-to-metal σ donation that increases the effective charge of the bound N atoms and stabilizes the N 1s core electrons. In contrast, the phenazine bridge N pre-edge peak is found at a lower energy due to stabilization of the low energy electron accepting orbital localized on the phenazine motif. While no sensitivity to ground state electronic coupling between the individual molecular subunits was observed, the spectra are sensitive to structural distortions of the tpphz bridge. These results demonstrate N K-edge XANES as a local probe of electronic structure in large bridging ligand motifs, able to distinctly investigate the ligand-centered orbitals involved in metal-to-ligand and ligand-to-ligand electron transfer following light absorption.

  View details for DOI 10.1063/5.0192809

  View details for PubMedID 38415835

• Optically Induced Anisotropy in Time-Resolved Scattering: Imaging Molecular-Scale Structure and Dynamics in Disordered Media with Experiment and Theory. Physical review letters Montoya-Castillo, A., Chen, M. S., Raj, S. L., Jung, K. A., Kjaer, K. S., Morawietz, T., Gaffney, K. J., van Driel, T. B., Markland, T. E. 2022; 129 (5): 056001

  Abstract

  Time-resolved scattering experiments enable imaging of materials at the molecular scale with femtosecond time resolution. However, in disordered media they provide access to just one radial dimension thus limiting the study of orientational structure and dynamics. Here we introduce a rigorous and practical theoretical framework for predicting and interpreting experiments combining optically induced anisotropy and time-resolved scattering. Using impulsive nuclear Raman and ultrafast x-ray scattering experiments of chloroform and simulations, we demonstrate that this framework can accurately predict and elucidate both the spatial and temporal features of these experiments.

  View details for DOI 10.1103/PhysRevLett.129.056001

  View details for PubMedID 35960558

• Angstrom-Resolved Interfacial Structure in Buried Organic-Inorganic Junctions PHYSICAL REVIEW LETTERS Schwartz, C. P., Raj, S. L., Jamnuch, S., Hull, C. J., Miotti, P., Lam, R. K., Nordlund, D., Uzundal, C. B., Das Pemmaraju, C., Mincigrucci, R., Foglia, L., Simoncig, A., Coreno, M., Masciovecchio, C., Giannessi, L., Poletto, L., Principi, E., Zuerch, M., Pascal, T. A., Drisdell, W. S., Saykally, R. J. 2021; 127 (9)

  View details for DOI 10.1103/PhysRevLett.127.096801

  View details for Web of Science ID 000688553600006

• The liquid state of carbon CHEMICAL PHYSICS LETTERS Hull, C. J., Raj, S. L., Saykally, R. J. 2020; 749

  View details for DOI 10.1016/j.cplett.2020.137341

  View details for Web of Science ID 000532697300008

• Free Electron Laser Measurement of Liquid Carbon Reflectivity in the Extreme Ultraviolet PHOTONICS Raj, S. L., Devlin, S. W., Mincigrucci, R., Schwartz, C. P., Principi, E., Bencivenga, F., Foglia, L., Gessini, A., Simoncig, A., Kurdi, G., Masciovecchio, C., Saykally, R. J. 2020; 7 (2)

  View details for DOI 10.3390/photonics7020035

  View details for Web of Science ID 000551229300013

• Early time dynamics of laser-ablated silicon using ultrafast grazing incidence X-ray scattering CHEMICAL PHYSICS LETTERS Hull, C., Raj, S., Lam, R., Katayama, T., Pascal, T., Drisdell, W. S., Saykally, R., Schwartz, C. P. 2019; 736

  View details for DOI 10.1016/j.cplett.2019.136811

  View details for Web of Science ID 000490975500002

• Two-photon absorption of soft X-ray free electron laser radiation by graphite near the carbon K-absorption edge CHEMICAL PHYSICS LETTERS Lam, R. K., Raj, S. L., Pascal, T. A., Pemmaraju, C. D., Foglia, L., Simoncig, A., Fabris, N., Miotti, P., Hull, C. J., Rizzuto, A. M., Smith, J. W., Mincigrucci, R., Masciovecchio, C., Gessini, A., De Ninno, G., Diviacco, B., Roussel, E., Spampinati, S., Penco, G., Di Mitri, S., Trovo, M., Danailov, M. B., Christensen, S. T., Sokaras, D., Wengk, T., Coreno, M., Poletto, L., Drisdell, W. S., Prendergast, D., Giannessi, L., Principi, E., Nordlund, D., Saykally, R. J., Schwartz, C. P. 2018; 703: 112-116

  View details for DOI 10.1016/j.cplett.2018.05.021

  View details for Web of Science ID 000433247400018

• Soft X-Ray Second Harmonic Generation as an Interfacial Probe PHYSICAL REVIEW LETTERS Lam, R. K., Raj, S. L., Pascal, T. A., Pemmaraju, C. D., Foglia, L., Simoncig, A., Fabris, N., Miotti, P., Hull, C. J., Rizzuto, A. M., Smith, J. W., Mincigrucci, R., Masciovecchio, C., Gessini, A., Allaria, E., De Ninno, G., Diviacco, B., Roussel, E., Spampinati, S., Penco, G., Di Mitri, S., Trovo, M., Danailov, M., Christensen, S. T., Sokaras, D., Weng, T., Coreno, M., Poletto, L., Drisdell, W. S., Prendergast, D., Giannessi, L., Principi, E., Nordlund, D., Saykally, R. J., Schwartz, C. P. 2018; 120 (2): 023901

  Abstract

  Nonlinear optical processes at soft x-ray wavelengths have remained largely unexplored due to the lack of available light sources with the requisite intensity and coherence. Here we report the observation of soft x-ray second harmonic generation near the carbon K edge (∼284  eV) in graphite thin films generated by high intensity, coherent soft x-ray pulses at the FERMI free electron laser. Our experimental results and accompanying first-principles theoretical analysis highlight the effect of resonant enhancement above the carbon K edge and show the technique to be interfacially sensitive in a centrosymmetric sample with second harmonic intensity arising primarily from the first atomic layer at the open surface. This technique and the associated theoretical framework demonstrate the ability to selectively probe interfaces, including those that are buried, with elemental specificity, providing a new tool for a range of scientific problems.

  View details for DOI 10.1103/PhysRevLett.120.023901

  View details for Web of Science ID 000419478800006

  View details for PubMedID 29376703