A Threshold-Based Approach to Calorimetry in Helium Droplets: Measurement of Binding Energies of Water Clusters

Helium dropletbeam methods have emerged as a versatile technique that can be used to assemble a wide variety of atomic and molecular clusters. We have developed a method to measure the binding energies of clusters assembled in helium droplets by determining the minimum droplet sizes required to assemble and detect selected clusters in the spectrum of the dopeddropletbeam. The differences in the droplet sizes required between the various multimers are then used to estimate the incremental binding energies. We have applied this method to measure the binding energies of cyclic waterclusters from the dimer to the tetramer. We obtain measured values of D0 that are in agreement with theoretical estimates to within ∼20%. Our results suggest that this threshold-based approach should be generally applicable using either mass spectrometry or optical spectroscopy techniques for detection, provided that the clusters selected for study are at least as strongly bound as those of water, and that a peak in the overall spectrum of the beam corresponding only to the cluster chosen (at least in the vicinity of the threshold) can be located

Carbon dots for multiphoton bioimaging

通讯作者地址: Sun, YP (通讯作者), Clemson Univ, Dept Chem, Clemson, SC 29634 USA 地址: 1. Clemson Univ, Dept Chem, Clemson, SC 29634 USA 2. Clemson Univ, Lab Emerging Mat & Technol, Clemson, SC 29634 USA 电子邮件地址: [email protected] nanoparticles upon simple surface passivation exhibit bright photoluminescence. Reported here is a new finding that these carbon dots are also strongly two-photon luminescent with pulsed laser excitation in the near-infrared. The experimentally measured two-photon absorption cross-sections are comparable to those of the high-performance semiconductor quantum dots already available in the literature. The two-photon luminescence microscopy imaging of human breast cancer cells with internalized carbon dots is demonstrated

Quantum-sized carbon dots for bright and colorful photoluminescence

通讯作者地址: Sun, YP (通讯作者), Clemson Univ, Dept Chem, Clemson, SC 29634 USA 地址: 1. Clemson Univ, Dept Chem, Clemson, SC 29634 USA 2. Clemson Univ, Lab Emerging Mat & Technol, Clemson, SC 29634 USA 电子邮件地址: [email protected]

Manufacture of syntactic foams using starch as binder: post-mold processing

Syntactic foam manufacturing method, ‘post-mold processing,’ based on the buoyancy of hollow microspheres was studied for potential building material applications. The post-mold processing involves mixing starch particles and ceramic hollow microspheres in water. It was found starch particles tend to adhere to hollow microspheres, forming agglomerations, during mixing. It was also found that “volume fraction of starch particles on a microsphere making a relative density of 1.0” (VFSMRD) is an indicator for mixture volume transitions. Both the maximum total volume expansion of mixture and a transition in formation, after phase separation, of mixture volume in water referred to as “top phase” in a mixing container were taken place at a calculated VFSMRD. It was found that hollow microsphere size effect on attracting starch particles was relatively high but IBVMS effect was not significant. Also, no effect of water volume for a given diameter of cylindrical container was found. Starch-microsphere inter-distance was discussed and considered to be an important parameter affecting starch content in an agglomeration. A Simple Cubic cell model for the starch-microsphere inter-distance was adopted to quantitatively explain various effects on starch content in agglomeration such as hollow microsphere size, initial bulk volume of hollow microspheres (IBVMS), and water volume. Further, the following were found for manufactured syntactic foams: (a) volume fraction of starch in foam is of linear relation with starch content before mixing for a given experimental data range and (b)shrinkage is relatively high for small hollow microspheres with high starch content

Infrared spectroscopy of the ν3 band of C3 in helium droplets

The C3 molecule is an important species known to participate in key chemical reactions in combustion and astrochemistry. Its occurrence in environments of interest, its intramolecular physics, and its intermolecular reactivity have been areas of extensive and ongoing study. Much of the interest in C3 is related to investigating its interactions with other species relevant to combustion processes or astrochemistry. Helium droplet methods offer a promising route to assemble and study a wide variety of novel complexes, clusters, and adducts made from C3. Here we report the results of our recent efforts to dope cold helium droplets with C3 molecules and record the rotationally-resolved infrared spectrum of the embedded C3. The spectrum consists of P(2), R(0), and R(2) lines well-described by a linear rotor Hamiltonian with ν0 = 2039.09(2) cm-1, B = 0.204(5) cm-1, and T = 0.37 K. The B rotational constant of the C3 molecule is found to be reduced from its gas-phase value by a factor of 2.1 due to rotational following by the helium solvent