Planarity of para Hexaphenyl

URL:http://link.aps.org/doi/10.1103/PhysRevLett.82.3625 DOI:10.1103/PhysRevLett.82.3625We present experimental and theoretical findings on the geometry of polycrystalline para hexaphenyl via Raman scattering. The planarity of the molecule is affected by hydrostatic pressure and temperature. Our studies indicate that the potential energy curve which governs the torsional motion between neighboring phenyl rings is “W” shaped. We determine the activation energy to promote the molecule from a nonplanar to a planar state to be 0.04 eV, in good agreement with our quantum chemical calculations. From the relative intensities of the 1280cm-1 to the 1220cm-1 Raman modes we show that high pressure planarizes the molecules, modifying the “W”-shaped potential energy curve to a “U”-shaped one.We acknowledge the financial support from U.S. Army Grant No. DAAL03-92-0381, University of Missouri Research Board and Österreichische Nationalbank (Project No. 6608)

Overview of the MOSAiC expedition: Physical oceanography

Arctic Ocean properties and processes are highly relevant to the regional and global coupled climate system, yet still scarcely observed, especially in winter. Team OCEAN conducted a full year of physical oceanography observations as part of the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC), a drift with the Arctic sea ice from October 2019 to September 2020. An international team designed and implemented the program to characterize the Arctic Ocean system in unprecedented detail, from the seafloor to the air-sea ice-ocean interface, from sub-mesoscales to pan-Arctic. The oceanographic measurements were coordinated with the other teams to explore the ocean physics and linkages to the climate and ecosystem. This paper introduces the major components of the physical oceanography program and complements the other team overviews of the MOSAiC observational program. Team OCEAN’s sampling strategy was designed around hydrographic ship-, ice- and autonomous platform-based measurements to improve the understanding of regional circulation and mixing processes. Measurements were carried out both routinely, with a regular schedule, and in response to storms or opening leads. Here we present alongdrift time series of hydrographic properties, allowing insights into the seasonal and regional evolution of the water column from winter in the Laptev Sea to early summer in Fram Strait: freshening of the surface, deepening of the mixed layer, increase in temperature and salinity of the Atlantic Water. We also highlight the presence of Canada Basin deep water intrusions and a surface meltwater layer in leads. MOSAiC most likely was the most comprehensive program ever conducted over the ice-covered Arctic Ocean. While data analysis and interpretation are ongoing, the acquired datasets will support a wide range of physical oceanography and multi-disciplinary research. They will provide a significant foundation for assessing and advancing modeling capabilities in the Arctic Ocean

Tuning Intermolecular Interactions: A Study of the Structural and Vibrational Properties of p-Hexaphenyl under Pressure

Hydrostatic pressure is used to modulate the intermolecular interactions in the conjugated oligophenyl, parahexaphenyl. These interactions affect the structural properties and also cause changes in the molecular geometry that directly alter the electronic properties. We use Raman spectroscopy to investigate the nature of the structural changes. Our Raman studies in the temperature range of 12 K to 300 K, under pressures up to 70 kbar, indicate that the potential energy of two neighboring phenyl rings as a function of the torsional angle is W -shaped. The libration of the phenyl rings between the two minima of the W -shaped potential can be modulated by either promoting the molecule to a higher energy state (activation energy of 0.045 eV) by raising the temperature or by decreasing the intermolecular separation, which makes the potential more U -shaped. Both these situations make the molecule seem more planar. We infer the shape of the potential from the relative intensity of the inter-ring C-C stretch Raman mode at 1280 cm-1 to the C-H bending mode at 1220 cm-1 (I1280/I1220). These results are interpreted within the framework of ab initio electronic and vibrational spectra calculations of a biphenyl molecule. We have also conducted X-ray studies to check the sample purity

High Pressure Studies on the Planarity of Para-hexaphenyl

We present experimental and theoretical findings on the geometry of para-hexaphenyl (PHP) molecules in polycrystalline powder. A new method to assess the planarity of PHP via Raman spectroscopy is presented. Based on this method we describe a W-shaped potential energy curve which governs the torsional motion between neighboring phenyl rings. We determine the activation energy to promote PHP from a non-planar to a planar state to be 0.04 eV, in good agreement with our quantum chemical calculations. Finally we are able to experimentally planarize the molecules by the application of hydrostatic pressure, which modifies the W-shaped potential energy curve to a U-shaped one

Raw data of GPS position and sea-surface temperature recorded by 44 Southtek NOMAD drifting buoys in the marginal ice zone north of Svalbard in 2022

44 Southtek Iridium GPS drifters of types Offshore NOMAD-T V3 (33) and Offshore NOMAD V2 (11) were deployed in the marginal ice zone northwest of Svalbard as part of RV Polarstern expedition PS131 (ATWAICE) in July-August 2022. In addition to GPS position and time, the 33 NOMAD-T buoys also measured sea-surface temperatures. The 44 buoys were used for a total of 48 individual deployments, including 4 redeployments of recovered instruments, to either mark and track non-iridium instruments (6), to mark important sites (2), to track individual ice floes (1), or to elucidate the surface ocean currents as a complement to measurements obtained by the towed Triaxus system (31) or the ship-based CTD (8). The buoys were either thrown over board into open water, placed on sea ice, or attached to instruments. The measurement and transmission intervals were between 1 hour and 15 minutes, and were also partly reconfigured during operation. The drifter data were downloaded directly on board and displayed in the ship's Mapviewer software in near-real time, to facilitate navigation and to support the scientific program in decision-making. The attached .zip archive contains the original data files obtained from the Southtek server, which were partially modified to account for the 4 redeployments (indicated by "redeployed" in the filename), and to fill a data gap caused by an iridium data provider issue (indicated by "merged" in the filename). The files still include the deck test data, which needs to be removed according to the attached table with deployment metadata (including deployment time and position)

Raw data from Triaxus topAWI (towed ocean profiler of the AWI) during RV POLARSTERN cruise PS131

The MacArtney Triaxus extended version is a remotely operated towed vehicle (ROTV). It is towed behind the ship between 2 and 10 knots and can undulate in a saw tooth pattern between a few meters below the surface and 350m depth. The umbilical provides power and a fiber optic link to sensors that are mounted on the Triaxus (see SensorWeb). The data collected by the sensors were recorded on separate computers, one computer per sensor (including the flight information from the Triaxus itself). Thus, there are 7 separate data streams saved in separate folders plus a folder with metadata information about the different dives. During long Triaxus operations, new data files would be started approximately every 4 hours, because some of the employed software programs do not allow for backing up of the files while they are still being written to. A heavy weight (depressor) was employed directly behind the ship to pull the umbilical below the water line before sea ice can close in behind the ship. In addition to a few test dives, three transects across the marginal ice zone north of Svalbard (Yermak Plateau) were collected on PS131 in July/August 2022

Raw physical oceanography and current meter data from mooring 79N2-2 in the Greenland Sea, September 2017 - September 2021

Time-series data of physical oceanography and ocean current velocities were obtained from mooring 79N2-2 in the Greenland Sea close to the calving front of the 79 North Glacier between September 2017 and September 2021. The mooring was deployed during RV Polarstern expedition PS109, and recovered during Danish coast guard patrol vessel HDMS Triton expedition TRITON2021. The attached archive contains raw data files of three Seabird SBE37 MicroCATs (nominal depths: 235m, 375m, 393m; sampling interval 15min to 1h), five SBE56 temperature loggers (nominal depths: 270m, 305m, 340m, 436m, 466m; sampling interval 30s), one RDI 1200kHz Workhorse ADCP (nominal depth: 385m; sampling interval 1.5h), and one RDI 75kHz Longranger ADCP (nominal depth: 456m; sampling interval 1h). Auxiliary information such as sensor calibration sheets, protocols, mooring diagrams, and schedule files are also provided, if applicable. The surface part of the mooring, consisting of one SBE37IMP MicroCAT and four SBE39plus-IM that were originally connected to a data logger via an inductive modem loop, was lost. The data logger, which was still attached to the main mooring line just below the weak link, could be recovered, and had recorded 3.5 months of instrument data

Raw data files from autonomous instruments installed on Floe South in the marginal ice zone northwest of Svalbard in July 2022 as part of RV POLARSTERN expedition PS131 (ATWAICE)

During Polarstern expedition PS131 (ATWAICE: ATlantic WAter pathways to the ICE), a large number of autonomous instruments were installed on three representative ice floes across the marginal ice zone northwest of Svalbard in July 2022. The aim was to investigate sea ice summer melt processes, with a focus on the contribution of the Atlantic water inflow into the region. The attached .zip file includes raw data files obtained from all instruments deployed on the southernmost floe, also referred to as Floe South. Depending on the instrument, the data were transmitted via satellite, collected on internal memory, or both. The instruments were installed on Floe South on 14 July 2022, revisited for maintenance on 21 July 2022, and partially recovered on 31 July 2022. The sensors included 1 ADCP to measure ocean currents, a CTD buoy (SIT) with 5 SBE37IMP, a SIMBA- and a SIMB-type ice mass balance buoy to determine ice surface and bottom melt, an OpenMetBuoy (OMB) and iridium IMU logger for wave detection, two GPS drifters, and 2 timelapse cameras to document surface changes. All instruments performed as expected. All instruments except one OpenMetBuoy were recovered before leaving the study area on 31 July. The processed data will be provided and linked to when available

Raw data files from autonomous instruments installed on Floe North in the marginal ice zone northwest of Svalbard in July 2022 as part of RV POLARSTERN expedition PS131 (ATWAICE)

During Polarstern expedition PS131 (ATWAICE: ATlantic WAter pathways to the ICE), a large number of autonomous instruments were installed on three representative ice floes across the marginal ice zone northwest of Svalbard in July 2022. The aim was to investigate sea ice summer melt processes, with a focus on the contribution of the Atlantic water inflow into the region. The attached .zip file includes raw data files obtained from all instruments deployed on the northernmost floe, also referred to as Floe North. Depending on the instrument, the data were transmitted via satellite, collected on internal memory, or both. The instruments were installed on Floe North on 13 July 2022, revisited for maintenance on 20 July 2022, and partially recovered on 30 July 2022. The sensors included 3 ADCPs in different configurations to measure ocean currents, a CTD buoy (SIT) with 6 SBE37IMP and an ECO Triplet fluorometer, a HOBO under-ice conductivity chain, 3 ice mass balance buoys (IMBs) of different types to determine ice surface and bottom melt, a radiation station equipped with 3 TriOS RAMSES radiometers to measure albedo and the under-ice light field, a Campbell Scientific weather station for atmospheric conditions, an OpenMetBuoy (OMB) and IMU logger for wave detection, a handful of GPS drifters to mark instruments, and 4 timelapse cameras to document surface changes. All instruments performed as expected, except one S1000 ADCP that failed due to power issues. All but three instruments (one OpenMetBuoy, one SVP, and one IMB) were recovered before leaving the study area on 30 July. The processed data will be provided and linked to when available