Zeeman experiments on the 3Eu α 1A1g transition of platinum porphein in an n-alkane single crystal at 4.2

We report absorption spectra from the ground state to the photoexcited triplet state of platinum porphin (PtP) in single crystals of n-octane (C₈) and n-decane (C₁₀) at 4.2 K, with and without a magnetic field. For PtP in C₁₀ the same transition was studied in emission. From the experiments, values are derived of the spin-orbit coupling parameter Z, the crystal field splitting δ and the orbital angular momentum A for PtP in the two hosts: Z = 76 ± 2 cm^?1 (C₈, C₁₀), δ = 71 ± 1 cm^?1 (C₈), 55 ± 1 cm^?1 (C₁₀) and A = 1.6 ± 0.1 (C₈, C₁₀). For the ratio of the in-plane and the z-polarized electric dipole transition moments we obtain ¦Mx,y¦/¦Mz¦=76± 0.3 (C₈).     

Microwave spectrum of cyclohexanone

The rotational spectrum of cyclohexanone has been observed within the frequency region from 18.0 to 40.0 GHz. Transitions in the ground state and six excited states have been assigned. The ground state rotational constants are (in MHz) A = 4195.316 +- 0.059, B = 2502.627 ± 0.005 and C = 1754.443 ± 0.005.From information obtained from relative intensity measurements, these excited states are estimated to be ~ 100 cm^?1 above the ground state for the first excited state of the ring-bending mode and ~ 180 cm^?1 for the first excited state of the ring-twisting mode.     

Microwave spectrum of 3-nitrothiophene

The microwave spectrum of 3-nitrothiophene has been studied in the frequency region 26.5–40.0 GHz. The rotational transitions of the ground state and the first six torsionally excited states have been assigned. The ground state rotational constants have been determined to be A_o=4622.61 ± 0.07 MHz, B_o = 1231.751 ± 0.001 MHz and C_o = 973.062 ± 0.001 MHz. The planarity of the molecule has been demonstrated. The first torsional frequency and the barrier to internal rotation of the nitro group have been estimated as 60 cm^?1 and 3.8 kcal/mole, respectively.     

Microwave spectra and dipole moments of bicyclo [2.2.1]-hepta-7-one and bicyclo [2.2.1]hept-2-en-7-one

The microwave spectra of bicycle [2.2.1] hepta-7-one (I), bicyelo [2.2.1] hept-2-en-7-one (II), and exo-5,6-bisdeuteriobicyclo [2.2.1] hept-2-en-7-one (III) have been recorded in the region between 26.5 and 40.0 GHz. The rotational constants in the order A, B, C for the title compounds are 2773.24±0.31, 2301.74±0.04, and 2133.96±0.02 (I); 2979.22±0.08, 2418.60±0.01, and 2235.51±0.01 (II); and 2789.67±0.06, 2385.24±0.01, and 2150.60±0.01 (III). The rotational constants of four vibrationally excited states were also determined for (II). Quadratic Stark effect measurements on the 7₁₆ ← 6₁₅ transition of (I) gave ¦μ_a¦=2.99±0.03. Similar measurements on two 5 ← 4 and 4 ← 3 transitions of (II) gave ¦μ_a¦=2.88±0.03, ¦μ_b¦=0.39±0.03, ¦μ_c¦=0, and ¦μ_total¦=2.91±0.04.     

Kinetics of Depletion of Electronically Excited Ti Atom by CH4, C2H2, C2H4 and C2H6

The kinetics of depletion of ground state Ti(a³F) and electronically excited state Ti(a⁵F) upon interactions with CH₄, C₂H₂, C₂H₄, and C₂H₆ are studied in a fast-flow reactor at a He pressure of 0.70 Torr. No depletion of ground state Ti(a³F) was observed upon interaction with all hydrocarbons studied here. Two alkanes, CH₄ and C₂H₆, were also quite inert for depletion of the excited state Ti(a⁵F), On the other hand, C₂H₂ and C₂H₄ deplete the excited state Ti(a⁵F) very efficiently. Rate constants were determined to be (266 ± 86) and (476 ± 88) × 10^?12 cm³s^?1 for Ti(a⁵F) + C₂H₄ and Ti(a⁵F) + C₂H₂, respectively. These large rate constants compared with the ground state Ti were explained by an electron donor-acceptor interaction model that works in the interaction between C₂H₄ or C₂H₂ and the excited state with unfilled 4s orbital.     

Construction and applications of symmetrized valence bond wave functions

A method constructing symmetry-adapted bonded Young tableau bases is proposed, based on the symmetry properties of bonded tableaus and the projection operator associated with a point group. Several examples including the ground states and π excited states of O₃⁻, O₃, O₃⁺, and C₃⁻ are shown for instruction to construct the symmetrized valence bond (VB) wave function. Excitation energies of transitions from the ground states to π excited states of O₃⁻, C₃H₅, and C₃⁻ are calculated with an optimized symmetrized valence bond wave function in the σ–π separation approximation. Good agreement between the VB and experimental excitation energies is observed. The bonding features of the ground state and the first π excited singlet and triplet states for S₃ are discussed according to bonding populations from VB calculations. Both the singlet-biradical and the dipole structures have significant contributions to the ground state X ¹A₁ of S₃, while the excited state 1 ¹B₂ is essentially composed of the dipole structures, and the 1 ³B₂ excited state is comprised from a triplet-biradical structure. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66 : 1–7, 1998     

Microwave spectrum,centrifugal distortion,internal rotation and excited torsional states of isobutene

The microwave spectrum of isobutene has been recorded from 10 to 35 GHz. From the analysis of the ground and first two excited torsional state splittings, the following internal rotation parameters were calculated: V₃ = 2170 cal mol.^?1, V'₁₂ = ?210 cal. mol.^?1, I_α = 3.18amu Ų and angle (methyl-top to b-axis) 58.21°. Centrifugal distortion parameters were also obtained for the ground state.     

Microwave spectrum and rotational isomers of epifluorohydrin

The microwave spectra of three rotational isomers of epifluorohydrin are Presented. The ground and 3 excited torsional states of one of the two gauche rotamers (III), and the ground states of the other gauche and cis rotamers (I & II), have been observed. The values of the ground state rotational constants. A, B, and C for rotamers I, II and III are 14 662.8, 3129.4, 2863.3; 10 645.8, 4050.2, 3679.1; and 14 833.1, 3210.2, 2933.9 MHz. The gaseous phase dipole components for the most abundant rotamer (III) are μ_a = 0.99 ± .02, μ_b = 2.90 ± .01 and μ_c = 0.0 ± .3, giving μ = 3.08 ± .02 D.     

The rotational spectrum of the hydrogen-bonded heterodimer H2O…HF in the frequency range 40–80 GHz

The μ_a R-branch rotational spectra of the ground and first excited states of the three lowest vibrational modes of the H₂O…HF heterodimer have been observed in the frequency range 40–80 GHz. Coriolis perturbations between the ground vibrational state (υ = 0) and the first excited state of the out-of-plane bending vibration (υ_β(0) = 1) show that for a given J the K₋₁ = 2 levels of υ_β(0) = 1 lie approximately 3 cm⁻¹ above the K₋₁ = 3 levels of υ = 0. The vibrational separation between these two states is estimated to be 70±3 cm⁻¹. This value is consistent with those determined by other methods and reinforces the conclusion that ν_β(0) is governed by a double-minimum potential energy function with the quantitative form previously published. A perturbation is also observed in the first excited state of the hydrogen-bond stretching vibration υ_σ = 1. This manifests itself as a large, negative centrifugal distortion constant D_JK = −8.5 MHz compared with 2 MHz in the other vibrational states.     

Spectra and structure of small ring compounds: Part XXX. Microwave spectrum of 1,1-difluoro-1-silacyclopent-3-ene

The microwave spectrum of 1,1-difluoro-l-silacyclopent-3-ene has been recorded from 26.5 to 40.0 GHz. Only A-type transitions were observed. The R-branch assignments have been made for the ground state and the first three excited states of the ring puckering vibration. It is shown that the five-membered ring structure is planar from the values of the components of the dipole moment, as well as from the value of the inertial defect as a function of the ring puckering quantum number. From the relative intensity measurements, it is concluded that the first excited state of the ring puckering vibration has a frequency of 38 ±7 cm^?1 and that the vibration is nearly harmonic. The components of the dipole moment were determined by the Stark effect to be μ_a = 2.02 ±0.06 D, μ_b = 0, and μ_c = 0.0 ±0.09 D. All of the observed data are consistent with a molecule of C_2v symmetry and the possible reasons for this structure are discussed.     

Infrared photodetachment measurements near thresholds of C−

The relative cross section has been measured in the threshold regions of the following transitions: C^?(⁴S) + hv → C³P_0,1,2) + e^? and C^?(²D) + hv → C(¹D) + e^?. The electron affinity of carbon is determined EA(C) = 1.2629 ± = 0.0003 eV, and the binding energy of the metastable C^?(²D) state with respect to the C(³P₀) ground state is 0.033 ± 0.001 eV.     

Bonding in the ground state and excited states of copper-alkene complexes

The ground state and ¹B₂ excited state of Cu(C₂H₄)⁺ and of CuX(C₂H₄) (X  F, Cl) have been investigated by the Hartree-Fock-Slater (HFS) method. The main metal-ligand interactions in the ground state are ethene π → Cu 4s donation and Cu 3d_π → ethene π^* backdonation, which have comparable contributions to the metal-ligand bond strength. The excitation of CuX(C₂H₄) does not involve an alkene π → metal charge transfer (LMCT), but instead is metal 3d → alkene π^* charge transfer (MLCT) in character. The implications for the photochemistry of olefin-copper(I) complexes are discussed.     

Preparation and photochemical properties of polymethacrylic esters of para-acylated 2-phenoxyethanols

For studying the photochemistry of carbonyl chromophores in the side-chain, methacrylic esters of para-acylated 2-phenoxyethanols (CH₂ = C(CH₃) · CO · O · CH₂ · CH₂O · C₆H₄ · CO · R), soluble copolymers with styrene and soluble homopolymers were prepared. Comparison of low temperature emission spectra of model compounds, homopolymers and copolymers doped in polystyrene film indicated some interaction between the excited and the ground state structural units in homopolymers. Quantum yield of main chain scission of copolymers of styrene with monomers 1–3 (R = CH₃, C₂H₅, C₆H₅) at 313 nm radiation in benzene were about 10^?4; the cross-linking was the main reaction for copolymer styrene/monomer 4 (R = C₆H₅CH₂). On exposure of copolymers styrene/monomers 1–4 and polystyrene doped with model compounds in film to 313 nm radiation in air, accelerated photo-oxidation occurs as well as cross-linking. Only chromophores of monomers 3 and 4 were effective as sensitizers of photochemical addition of maleic anhydride to benzene by radiation with γ > 340 nm. The difference in the efficiency between model compounds and copolymers on the one hand and a homopolymer on the other hand is due to self-quenching.     

The structure of 1,3-dichloropropyne as determined by gas electron diffraction and comparison with microwave data

The structure of 1,3-dichloropropyne has been studied by gas electron diffraction. The resulting parameters r_a have been converted into r_α^o distances. A geometrical structure has been fitted to these internuclear distances. Thus the following parameters (r_α^o) have been determined: r(C₁-Cl₁) = 1.629 (10) A, r(C₁C₂) = 1.201 (13) Å, r(C₃-Cl₂) = 1.791 (6) A, ∠(C₂-C₃-Cl₂) = 111.1° (1.0°), ∠(H-C₃-H) = 98.8° (3.1°), ∠(C₂-C₃-H) = 108.7° (3.2°). ∠(Cl₁-C₁C₂) = 176.6° (1.1°), ∠(C₁C₂-C₃) = 182.7° (1.4°). Inconsistencies have been detected between our results and the rotational constants reported by Günther and Zeil. Discussion of the problem including rotational constants of the first excited vibrational state leads to the conclusion that the observed discrepancies are due to temperature effects.     

Thermodynamics of the URuC system

Thermodynamic measurements by the electromotive force method were made on the binary intermetallic phases URu₃ and U₃Ru₅ and on the ternary carbides URu₃C_0.7 and U₂RuC₂ of the URu and the URuC systems between 950 and 1200 K using galvanic cells with CaF₂ single crystal electrolytes: U, UF₃¦CaF₂¦UF₃, URu₃, Ru; U, UF₃¦CaF₂¦UF₃, U₃Ru₅, URu₃; Ru, URu₃, UF₃¦CaF₂¦UF₃, URu₃C_0.7, Ru, C; U, UF₃¦CaF₂¦UF₃, URu₃C_0.7, U₂RuC₂, C. The Gibbs energies of formation of URu₃, U₃Ru₅, URu₃C_0.7 and U₂RuC₂ were evaluated from the measured electromotive force which give ^fΔG^o〈URu₃〉 = −199 100 + 35.9 T J mol^−1fΔG^o〈U₃Ru₅〉 = −398 600 + 43.6 T J mol^−1fΔG^o〈URu₃C_0.7〉 = −192 600 + 2.5 T J mol^−1fΔG^o〈U₂RuC₂〉 = −380 200 + 52.5 T J mol⁻¹ The implications of these thermodynamic data for the behaviour of the fission product ruthenium in irradiated carbide fuels are discussed.     

Microwave spectrum of propionyl chloride

The microwave spectrum of propionyl chloride has been investigated in the region 18.0–40.0 GHz, and transitions due to a cis conformer have been assigned. This form has a heavy atom planar configuration and the methyl group and the carbonyl oxygen atom are cis to each other. Using the substitution structures of propionic acid and acetyl chloride as molecular models for the propionyl chloride molecule, good agreement is found between observed and calculateò effective rotational constants. For the ³⁵Cl species satellite spectra assigned to the first four excited states of the C-C torsional mode have been observed together with the first excited state of the methyl torsional mode. The ground state spectrum has also been assigned for the ³⁷Cl species. Relative intensity measurements yielded the lowest C-C torsional vibration frequency of 86 ± 10 cm^?1. The CH₃ internal rotation frequency was found to be 197 cm^?1. Nuclear quadrupole coupling constants were determined for the ground state of the ³⁵Cl and ³⁷Cl species. From observed A-E splittings of ^bQ-branch transitions of the first excited state of the methyl torsional mode a barrier to internal rotation was estimated to be V₃ = 2480 ± 40 cal mol^?1 (867 ± 14 cm^?1).     

Microwave and far-IR spectra,conformational stability,molecular structure,barriers to internal rotation and ab initio calculations for the anticlinal conformer of trans-1-fluoro-2-butene

The microwave spectrum of trans-1-fluoro-2-butene, trans-(CH₃)HCCH(CH₂F), has been recorded in the region of 18.0–39.0 GHz. Both a-type R- and b-type Q-branch assignments have been made for the ground and first two vibrationally excited states of the asymmetric torsion for the gauche (anticlinal) conformer. The ground state rotational constants for this conformer are found to have the following values: A = 19,938.33±0.48, B = 2071.37±0.01, C = 2022.17±0.01 MHz. From an analysis of the internal rotational splittings of the Q-branches, the three-fold rotational barrier for the methyl group is determined to be 596±7 cm⁻¹ (1.70±0.02 kcal/mol). From the Stark effect the dipole moment components for the gauche conformer were determined to be |μ_a| = 1.86±0.01, |μ_b| = 1.16±0.01, |μ_c| = 0.31±0.05, and |μ_t = 2.21±0.01 D. The fundamental asymmetric torsion for the cis (synclinal) conformer has been observed in the far-IR spectrum of the vapor at 123.95 cm⁻¹ whereas that for the gauche conformer has been determined to occur at 82.8±5 cm⁻¹ based on relative intensity measurements obtained from the microwave spectrum. From these data the potential function which governs the internal rotation of the asymmetric top has been determined and the following potential constants have been evaluated: V₁ = −191±10, V₂ = 598±10, V₃ = 786±13, V₄ = 59±5, and V₆ = 79±5 cm⁻¹. These data are consistent with the more stable conformer having the fluorine atom cis (synclinal) to the double bond and lying 300±33 cm⁻¹ (858±94 cal/mol) lower in energy than the gauche rotamer. Utilizing ab initio calculations with the MP2/6-31G* basis set and the three rotational constants, r₀ structural parameters are estimated. Also, the barriers to conformer interconversion have been calculated with the RHF/3-21G, RHF/6-31G*, and MP2/6-31G* basis sets. All of these results have been compared to the similar quantities of some corresponding molecules.     

Theoretical studies on structures and electronic spectra of linear carbon chains C2nH+ (n = 1−5)

The density functional theory (DFT) and the complete active space self‐consistent‐field (CASSCF) method have been used for full geometry optimization of carbon chains C_2nH⁺ (n = 1–5) in their ground states and selected excited states, respectively. Calculations show that C_2nH⁺ (n = 1–5) have stable linear structures with the ground state of X³Π for C₂H⁺ or X³Σ^? for other species. The excited‐state properties of C_2nH⁺ have been investigated by the multiconfigurational second‐order perturbation theory (CASPT2), and predicted vertical excitation energies show good agreement with the available experimental values. On the basis of our calculations, the unsolved observed bands in previous experiments have been interpreted. CASSCF/CASPT2 calculations also have been used to explore the vertical emission energy of selected low‐lying states in C_2nH⁺ (n = 1–5). Present results indicate that the predicted vertical excitation and emission energies of C_2nH⁺ have similar size dependences, and they gradually decrease as the chain size increases. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Spectra and structure of small ring compounds: XXIX. Microwave spectrum of γ-butyrolactone

The microwave spectrum of γ-butyrolactone has been recorded from 12.4 to 40.0 GHz. Both A-type and B-type transitions were observed. The R-branch assignments have been made for the ground state and the first two excited states of the ring-puckering and the first excited state of the ring twisting modes. It is shown that the ring skeleton is non-planar from the magnitude of the μ_c component of the dipole moment as well as from the value of I_c?(I_a+I_b). From the relative intensity measurements of the ground and the excited state, the ring twisting mode appears to be governed by a double minimum potential. The dipole moment was determined to be 4.27±0.03 D with components of μ_a = 4.04±0.03 D, μ_b = 1.42±0.03 D, μ_c = 0.33±0.02 D. From an investigation of the Raman spectrum of the gas, the ring puckering vibration was found to have a frequency of 148 cm^?1, whereas the ring twisting mode was found at 225 cm^?1.     

Standard enthalpy of formation of fullerene bromide C60Br24

The enthalpy of the combustion of C₆₀Br₂₄ · 2Br₂ has been measured using a rotating-bomb calorimeter as follows: Δ _c H ⁰(C₆₀Br₂₄ · 2Br₂, cr) = (?25986 ± 166) kJ/mol. The result has been used to calculate the standard enthalpy of formation, ΔfH ⁰(C₆₀Br₂₄ · 2Br₂, cr) = (2375 ± 166) kJ/mol. The enthalpies of formation of C₆₀Br₂₄ (cr) and dissociation of the C-Br bond have been estimated. The latter value has been compared with enthalpies for the C-X (X = H, F, Cl, Br) bonds in fullerene derivatives and organic compounds.