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Thermionic work functions and desorption energies for oxygen on polycrystalline W, Mo and Re filaments, discussing oxygen pressure and filament temperature
Rate coefficients for the reaction of NO3 radicals with a series of aromatic aldehydes were measured in a 7300 L simulation chamber at ambient temperature and pressure by relative and absolute methods. The rate coefficients for benzaldehyde (BA), ortho-tolualdehyde (O-TA), meta-tolualdehyde (M-TA), para-tolualdehyde (P-TA), 2,4-dimethyl benzaldehyde (2,4-DMBA), 2,5-dimethyl benzaldehyde (2,5-DMBA) and 3,5-dimethyl benzaldehyde (3,5-DMBA) were k 1 = 2.6 ± 0.3, k 2 = 8.7 ± 0.8, k 3 = 4.9 ± 0.5, k 4 = 4.9 ± 0.4, k 5 = 15.1 ± 1.3, k 6 = 12.8 ± 1.2 and k 7 = 6.2 ± 0.6, respectively, in the units of 10 -15 cm 3 molec. -1 s -1 at 298 ± 2 K. The rate coefficient k 13 for the reaction of the NO 3 radical with deuterated benzaldehyde (benzaldehyde-d1) was found to be half that of k 1 . The end product of the reaction in an excess of NO 2 was measured to be C 6 H 5 C(O)O 2 NO 2 . Furthermore, theoretical calculations of aldehydic bond energies and reaction pathways indicate that the NO 3 radical reacts primarily with aromatic aldehydes through the abstraction of an aldehydic hydrogen atom. The atmospheric implications of the measured rate coefficients are briefly discussed.
TaO2 is Rutile structured and crystallizes in the tetragonal P4_2/mnm space group. The structure is three-dimensional. Ta4+ is bonded to six equivalent O2- atoms to form a mixture of edge and corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles are 43°. There are two shorter (2.02 Å) and four longer (2.09 Å) Ta–O bond lengths. O2- is bonded in a distorted T-shaped geometry to three equivalent Ta4+ atoms.
Ta2O is alpha Po structured and crystallizes in the cubic I-43m space group. The structure is zero-dimensional and consists of six tantalum molecules and two Ta5O4 clusters. In each Ta5O4 cluster, there are two inequivalent Ta sites. In the first Ta site, Ta is bonded in a distorted single-bond geometry to one O atom. The Ta–O bond length is 1.84 Å. In the second Ta site, Ta is bonded in a tetrahedral geometry to four equivalent O atoms. All Ta–O bond lengths are 1.88 Å. O is bonded in a distorted linear geometry to two Ta atoms.
Ta4O crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. there are three inequivalent Ta sites. In the first Ta site, Ta is bonded in a square co-planar geometry to four equivalent O atoms. All Ta–O bond lengths are 2.30 Å. In the second Ta site, Ta is bonded in a single-bond geometry to four equivalent Ta and one O atom. All Ta–Ta bond lengths are 2.81 Å. The Ta–O bond length is 2.10 Å. In the third Ta site, Ta is bonded in a body-centered cubic geometry to eight equivalent Ta atoms. O is bonded to six Ta atoms to form a mixture of edge and corner-sharing OTa6 octahedra. The corner-sharing octahedral tilt angles are 0°.
Ta2O5 crystallizes in the orthorhombic Pmmm space group. The structure is three-dimensional. there are two inequivalent Ta5+ sites. In the first Ta5+ site, Ta5+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing TaO6 octahedra. The corner-sharing octahedra tilt angles range from 0–58°. There are two shorter (1.95 Å) and four longer (2.19 Å) Ta–O bond lengths. In the second Ta5+ site, Ta5+ is bonded to six O2- atoms to form corner-sharing TaO6 octahedra. The corner-sharing octahedra tilt angles range from 0–58°. There are a spread of Ta–O bond distances ranging from 1.85–2.09 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a linear geometry to two equivalent Ta5+ atoms. In the second O2- site, O2- is bonded in a trigonal planar geometry to three Ta5+ atoms. In the third O2- site, O2- is bonded in a linear geometry to two equivalent Ta5+ atoms. In the fourth O2- site, O2- is bonded in a linear geometry to two equivalent Ta5+ atoms.
Ta2O5 crystallizes in the monoclinic C2 space group. The structure is three-dimensional. Ta5+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ta–O bond distances ranging from 1.90–2.40 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to three equivalent Ta5+ atoms. In the second O2- site, O2- is bonded in a water-like geometry to two equivalent Ta5+ atoms. In the third O2- site, O2- is bonded in a 4-coordinate geometry to four equivalent Ta5+ atoms.
Ta2O5 crystallizes in the monoclinic Cm space group. The structure is two-dimensional and consists of two Ta2O5 sheets oriented in the (1, 0, 0) direction. there are two inequivalent Ta5+ sites. In the first Ta5+ site, Ta5+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ta–O bond distances ranging from 1.73–2.15 Å. In the second Ta5+ site, Ta5+ is bonded to six O2- atoms to form edge-sharing TaO6 octahedra. There are a spread of Ta–O bond distances ranging from 1.96–2.08 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to three Ta5+ atoms. In the second O2- site, O2- is bonded in a trigonal non-coplanar geometry to three Ta5+ atoms. In the third O2- site, O2- is bonded in a water-like geometry to two equivalent Ta5+ atoms. In the fourth O2- site, O2- is bonded in a trigonal non-coplanar geometry to three Ta5+ atoms. In the fifth O2- site, O2- is bonded in a single-bond geometry to one Ta5+ atom.
(TaO3)2(O2)7 crystallizes in the triclinic P1 space group. The structure is two-dimensional and consists of two oxygen molecules; one trioxidane molecule; and one TaO3 sheet oriented in the (0, 0, 1) direction. In the TaO3 sheet, Ta is bonded to five O atoms to form distorted corner-sharing TaO5 trigonal bipyramids. There are a spread of Ta–O bond distances ranging from 1.79–2.00 Å. There are three inequivalent O sites. In the first O site, O is bonded in a bent 150 degrees geometry to two equivalent Ta atoms. In the second O site, O is bonded in a single-bond geometry to one Ta atom. In the third O site, O is bonded in a bent 150 degrees geometry to two equivalent Ta atoms.
Ta10O9 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are ten inequivalent Ta sites. In the first Ta site, Ta is bonded in a 1-coordinate geometry to four O atoms. There are a spread of Ta–O bond distances ranging from 2.07–2.39 Å. In the second Ta site, Ta is bonded in a 1-coordinate geometry to four O atoms. There are a spread of Ta–O bond distances ranging from 2.13–2.39 Å. In the third Ta site, Ta is bonded to five O atoms to form distorted TaO5 trigonal bipyramids that share corners with two equivalent TaO5 square pyramids, corners with two equivalent TaO4 trigonal pyramids, an edgeedge with one TaO5 square pyramid, edges with two equivalent TaO5 trigonal bipyramids, and edges with two equivalent TaO4 trigonal pyramids. There are a spread of Ta–O bond distances ranging from 2.06–2.21 Å. In the fourth Ta site, Ta is bonded to four O atoms to form distorted TaO4 trigonal pyramids that share corners with two equivalent TaO5 square pyramids, corners with two equivalent TaO5 trigonal bipyramids, corners with two equivalent TaO4 trigonal pyramids, and edges with two equivalent TaO5 trigonal bipyramids. There are a spread of Ta–O bond distances ranging from 2.13–2.30 Å. In the fifth Ta site, Ta is bonded in a distorted single-bond geometry to four O atoms. There are a spread of Ta–O bond distances ranging from 2.06–2.66 Å. In the sixth Ta site, Ta is bonded to six O atoms to form distorted TaO6 octahedra that share corners with three equivalent TaO6 octahedra, edges with nine TaO6 octahedra, and edges with two equivalent TaO5 square pyramids. The corner-sharing octahedra tilt angles range from 0–2°. There are a spread of Ta–O bond distances ranging from 2.22–2.36 Å. In the seventh Ta site, Ta is bonded to six O atoms to form a mixture of distorted edge and corner-sharing TaO6 octahedra. The corner-sharing octahedra tilt angles range from 0–2°. There are a spread of Ta–O bond distances ranging from 2.26–2.49 Å. In the eighth Ta site, Ta is bonded to five O atoms to form distorted TaO5 square pyramids that share corners with three equivalent TaO6 octahedra, corners with two equivalent TaO5 trigonal bipyramids, corners with two equivalent TaO4 trigonal pyramids, edges with three TaO6 octahedra, edges with two equivalent TaO5 square pyramids, and an edgeedge with one TaO5 trigonal bipyramid. The corner-sharing octahedra tilt angles range from 0–3°. There are a spread of Ta–O bond distances ranging from 2.21–2.57 Å. In the ninth Ta site, Ta is bonded to six O atoms to form distorted TaO6 octahedra that share corners with three equivalent TaO6 octahedra, corners with three equivalent TaO5 square pyramids, edges with nine TaO6 octahedra, and an edgeedge with one TaO5 square pyramid. The corner-sharing octahedra tilt angles range from 1–4°. There are a spread of Ta–O bond distances ranging from 2.13–2.45 Å. In the tenth Ta site, Ta is bonded to six O atoms to form a mixture of distorted edge and corner-sharing TaO6 octahedra. The corner-sharing octahedra tilt angles range from 1–4°. There are a spread of Ta–O bond distances ranging from 2.27–2.35 Å. There are nine inequivalent O sites. In the first O site, O is bonded in a rectangular see-saw-like geometry to four Ta atoms. In the second O site, O is bonded in a 6-coordinate geometry to six Ta atoms. In the third O site, O is bonded to six Ta atoms to form edge-sharing OTa6 octahedra. In the fourth O site, O is bonded in a rectangular see-saw-like geometry to four Ta atoms. In the fifth O site, O is bonded to six Ta atoms to form a mixture of distorted edge and corner-sharing OTa6 octahedra. The corner-sharing octahedra tilt angles range from 1–2°. In the sixth O site, O is bonded in a 6-coordinate geometry to six Ta atoms. In the seventh O site, O is bonded to six Ta atoms to form a mixture of distorted edge and corner-sharing OTa6 octahedra. The corner-sharing octahedra tilt angles range from 0–4°. In the eighth O site, O is bonded to six Ta atoms to form a mixture of distorted edge and corner-sharing OTa6 octahedra. The corner-sharing octahedra tilt angles range from 0–4°. In the ninth O site, O is bonded to six Ta atoms to form a mixture of distorted edge and corner-sharing OTa6 octahedra. The corner-sharing octahedra tilt angles range from 1–2°.
TaO3 crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ta is bonded to twelve equivalent O atoms to form a mixture of face and corner-sharing TaO12 cuboctahedra. There are six shorter (2.24 Å) and six longer (2.34 Å) Ta–O bond lengths. O is bonded in a see-saw-like geometry to four equivalent Ta atoms.
Ta2O5 crystallizes in the orthorhombic Pbam space group. The structure is three-dimensional. Ta5+ is bonded to five O2- atoms to form distorted corner-sharing TaO5 trigonal bipyramids. There are a spread of Ta–O bond distances ranging from 1.83–2.08 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 150 degrees geometry to two equivalent Ta5+ atoms. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to two equivalent Ta5+ atoms. In the third O2- site, O2- is bonded in a linear geometry to two equivalent Ta5+ atoms.
Ta2O5 crystallizes in the orthorhombic Pmmn space group. The structure is three-dimensional. Ta5+ is bonded to six O2- atoms to form a mixture of corner and edge-sharing TaO6 octahedra. The corner-sharing octahedra tilt angles range from 1–29°. There are a spread of Ta–O bond distances ranging from 1.86–2.22 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a linear geometry to two equivalent Ta5+ atoms. In the second O2- site, O2- is bonded in a linear geometry to two equivalent Ta5+ atoms. In the third O2- site, O2- is bonded in a 3-coordinate geometry to three equivalent Ta5+ atoms.