Excess molar quantities of (a halogenated n-alkane + an n-alkane) A comparative study of mixtures containing either 1-chlorobutane or 1,4-dichlorobutane

Excess molar volumes V_m^E at 298.15 K were obtained, as a function of mole fraction x, for series I: {x1-C₄H₉Cl + (1 ? x)n-C_lH_{2l + 2}}, and II: {x1,4-C₄H₈Cl₂ + (1 ? x)n-C_lH_{2l + 2}}, for l = 7, 10, and 14. 10, and 14. The instrument used was a vibrating-tube densimeter. For the same mixtures at the same temperature, a Picker flow calorimeter was used to measure excess molar heat capacities C_{p, m}^E at constant pressure. V_m^E is positive for all mixtures in series I: at x = 0.5, V_m^E/(cm³ · mol^?1) is 0.277 for l = 7, 0.388 for l = 10, and 0.411 for l = 14. For series II, V_m^E of {x1,4-C₄H₈Cl₂ + (1 ? x)n-C₇H₁₆} is small and S-shaped, the maximum being situated at x_max = 0.178 with V_m^E(x_max)/(cm³ · mvl^?1) = 0.095, and the minimum is at x_min = 0.772 with V_m^E(x_min)/(cm³ · mol^?1) = ?0.087. The excess volumes of the other mixtures are all positive and fairly large: at x = 0.5, V_m^E/(cm³ · mol^?1) is 0.458 for l = 10, and 0.771 for l = 14. The C_{p, m}^Es of series I are all negative and |C_{p, m}^E| increases with increasing l: at x = 0.5, C_{p, m}^E/(J · K^?1 · mol^?1) is ?0.56 for l = 7, ?1.39 for l = 10, and ?3.12 for l = 14. Two minima are observed for C_{p, m}^E of {x1,4-C₄H₈Cl₂ + (1 ? x)n-C₇H₁₆}. The more prominent minimum is situated at x′_min = 0.184 with C_{p, m}^E(x′_min)/(J · K^?1 · mol^?1) = ?0.62, and the less prominent at x″_min = 0.703 with C_{p, m}^E(x″_min)/(J · K^?1 · mol^?1) = ?0.29. Each of the remaining two mixtures (l = 10 and 14) has a pronounced minimum at low mole fraction (x_min = 0.222 and 0.312, respectively) and a broad shoulder around x = 0.7.     

Modified low temperature solid state synthesis and photoluminescent properties of Y0.48Li1.5V1 ? x P x O4:Eu3+ (x = 0.2, 0.4, 0.6) nanophosphors

A modified low temperature solid state process has been proposed to systematically synthesize europium-doped yttrium phosphate-vanadates with general formula Y_0.48Li_1.5V_{1 ? x} P _x O₄:Eu³⁺ (x = 0.2, 0.4, 0.6). All the Y_0.48Li_1.5V_{1 ? x} P _x O₄:Eu³⁺ products were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The excitation and emission spectra were measured at room temperature. Y_0.48Li_1.5V_{1 ? x} P _x O₄:Eu³⁺ show the characteristic missions of Eu³⁺ (⁵ D ₀?⁷ F _{1, 2, 3, 4} transitions dominated by ⁵ D ₀?⁷ F ₂), intensities of the products were sensitive to the x value, and the x value had an obvious influence on the (⁵ D ₀?⁷ F ₂)/(⁵ D)₀?⁷ F ₁) intensity ratio of Eu³⁺. In addition, incorporation of Li⁺ ions in the phosphors reduce the amount of Y₂O₃, lower the cost of production, and cause a new phase Li₃VO₄.     

The photophysics of trans-stilbene

The fluorescence lifetime of trans-stilbene in dilute methylcyclohexane/iso-hexane solution has been measured and the mean S₁ radiative (k_F), radiationless (k_I) and cis-isomerization (k_C) rate parameters have been determined from ?90 to 60°C. S_i consists of a fluorescent trans (¹B_u^*) state (k_F⁰ = 6.0 × 10⁸ s^?1) which undergoes reversible thermal-activated rotational internal conversion (ΔH = 1.75 kcal mole^?1, ΔS = 10.6 cal deg^?1 mole^?1) to a non-fluorescent perp (¹A_g^*) state. p(¹A_g^*) lies 610 cm^?1 above t (¹B_u^*) with an intermediate S₁ potential maximum. p(¹A_g^*) undergoes internal conversion(k_I.^∞ = 5.8 × 10⁸ s^?1) to p (¹A_g) leading to cis-isomerization. This is the main isomerization channel over the whole temperature range.     

Synthesis of novel termetallic isopropoxides

Novel termetallic isopropoxides are reported which may be represented by the general formulae: [(PrⁱO)₃M(μ-OPrⁱ)₂Be(μ-OPrⁱ)₂Al(OPrⁱ)₂], [(PrⁱO)₂M(μ-OPrⁱ)₂Be(μ-OPrⁱ)₂Al(OPrⁱ)₂]₂ [where M = Ti(IV), Zr(IV) and Hf(IV)] and [(PrⁱO)₄M(μ-OPrⁱ)₂Be(μ-OPrⁱ)₂Al(OPrⁱ)₂] [where M = Nb(V) and Ta(V)]. Attempts to synthesize derivatives with the general formula, [(PrⁱO)₇M₂(μ-OPrⁱ)₂Be(μ-OPrⁱ)₂Al(OPrⁱ)₂] [where M = Ti(IV), Zr(IV) or Hf(IV)], were unsuccessful and in all such cases a mixture of M(OPrⁱ)₄ and [(PrⁱO)₃M(μ-OPrⁱ)₂Be(μ-OPrⁱ)₂Al(OPrⁱ)₂] was obtained. All these derivatives are soluble in common organic solvents and with the exception of titanium(IV) derivatives, they can be volatilised without noticeable disproportionation. These products have been characterized by elemental analyses, molecular weights, IR, ¹H NMR and (in representative cases) mass spectral studies also.     

Eu luminescence—a structural probe in BiCa4(PO4)3O, an apatite related phosphate

Eu³⁺ luminescence is studied in apatite-related phosphate BiCa₄(PO₄)₃O. Compositions of the formula Bi_1−xEu_xCa₄(PO₄)₃O [x=0.05, 0.1, 0.3, 0.5, 0.8 and 1.0] are synthesized and they are isostructural with parent BiCa₄(PO₄)₃O. Room temperature photoluminescence shows the various transitions ⁵D₀→⁷F_J(=0,1,2) of Eu³⁺. The emission results of compositions with different Eu³⁺ content show the difference in site occupancy of Eu³⁺ in Bi_1−xEu_xCa₄(PO₄)₃O. The intense ⁵D₀-⁷F₀ line at 574 nm for higher Eu³⁺ content is attributed to the presence of strongly covalent Eu-O bond that is possible by substituting Bi³⁺ in the Ca(2) site. This shows the preferential occupancy of Bi³⁺ in Ca(2) site and this has been attributed to the 6s² lone pair electrons of Bi³⁺. This is further confirmed by comparing the emission results with La_0.95Eu_0.05Ca₄(PO₄)₃O.     

Synthesis and coordination chemistry of tetrabutyldithioimidodiphosphinates

Butyl substituted imidodithiophosphinates R₂P(S)NP (S)R′₂ (R=ⁿBuⁱBu^sBuR′=ⁿBuⁱBu^sBu) have been synthesised via an HBr elimination reaction between R₂P(S)NH₂ and R′₂P(S)Br The compounds were characterised spectroscopically Crystallographic and spectroscopic studies reveal ⁿBu₂P(S)NHP(S)ⁿBu₂ and ^sBu₂P(S)NHP(S)ⁱBu₂ to be hydrogen bonded transoid dimers and ⁱBu₂P(S)NHP(S)ⁱBu₂ to be a transoid hydrogen bonded chain Reactions of the imidodithiophosphinates with ZnCl₂ or MCl₂COD gave the coordination complexes M[R₂P(S)NP (S)R′₂]₂ (R=ⁿBuⁱBu^sBuR′=ⁿBuⁱBu^sBuM=ZnPd: R=ⁿBuⁱBu^sBuPt).     

Fluorescence line narrowing spectroscopy of Eu in zinc-thallium-tellurite glass

The environment of Eu³⁺ in zinc-thallium-tellurite glass of the molar composition 60TeO₂-30TlO_0.5-9.9ZnO-0.1Eu₂O₃ was investigated by laser-induced fluorescence line narrowing (FLN) techniques using Eu³⁺ as a local site probe. From the site selective luminescence spectra of Eu³⁺ at 7 K, the energies of the Stark components of the ⁷F₁ and ⁷F₂ states were recorded and then the crystal field parameters B_nm were calculated assuming a C_2v site symmetry. The ratios B₂₂/B₂₀ and B₄₄/B₄₀ for each excitation energy within ⁷F₀-⁵D₀ transition were obtained and compared with the values calculated for Eu³⁺ in other types of glasses.     

Geometric and electronic structure of ground and excited states of groupVA diatomics. A theoretical LCGTO-MP-LSD study

LCGTO-MP-LSD calculation was performed for the ground and several low-lying excited states of homo- (N₂, P₂, As₂, and Sb₂) and hetero-nuclear (PN, AsN, AsP, AsSb, SbN, and SbP) groupVA diatomics. For all the systems the ground state is found to be¹Σ⁺. For N₂ and P₂, the¹Σ _g ⁺ ground state is followed by the³Σ _u ⁺ ,³Π _g ,³Δ _u ,¹Π _g , and¹Δ _u low-lying exited states while for As₂ the order is found to be³Σ _u ⁺ ,³Δ _u ,³Π _g ,¹Δ _u ,¹Π _g . Finally for Sb₂ the relative stability of excited states is³Σ _u ⁺ ,³Δ _u ,¹Δ _u ,³Π _g ,¹Π _g . For the hetero-nuclear diatomics the¹Σ⁺ ground state is, in the case of PN, AsN, AsP, SbN, and SbP, followed by the³Σ⁺,³Δ,³Π,¹Π and¹Δ low-lying excited states while for the AsSb diatomic an inversion of stability of the two last singlets occurs. The calculated spectroscopic parameters (Re, ωe, andDe) are in good agreement with all the available experimental results while, theTe values are overestimated by about 0.5 eV. Mulliken population analysis shows that both homo- and hetero-nuclear groupVA diatomics are essentially triple bonded systems.     

Kinetics of hydroquinone chemisorption at polycrystalline platinum electrodes: The effect of surface roughness

The rate of hydroquinone (HQ) chemisorption from aqueous H₂SO₄ onto annealed (smooth) and platinized (rough) polycrystalline Pt has been studied. Previously, equilibrium adsorption measurements indicated that at smooth Pt surfaces, adsorption of HQ at c_HQ ⩽ 0.1 mM yielded flat (η⁶)-oriented species while adsorption at c_HQ ⩾ 1 mM resulted in edge (2,3-η²)-attached intermediates. Edge-attached species were not formed efficiently at roughened Pt surfaces. The present data show that the rate of η⁶-HQ chemisorption was significantly lower at roughened than at smooth surfaces. Analysis of the rate data gave the following enthalpies and entropies of activation at smooth (sm) and platinized (pt) surfaces: ΔH^≠_sm,0.1mM = 12.5 kJ/mol; ΔH^≠_sm,2mM = 8.3 kJ/mol; ΔS^≠_sm,0.1mM = −83 J/mol K; ΔS^≠_sm,2mM = −117 J/mol K; ΔH^≠_pt,0.4mM = 12.5 kJ/mol; ΔH^≠_pt,2mM = 12.5 kJ/mol; ΔS^≠_pt,0.4mM = −92 J/mol K; ΔS^≠_pt,2mM = −100 J/mol K. The similarity between ΔH^≠_{pt,0.4 mM}, ΔH^≠_{pt,2 mM} and ΔH^≠_{sm,0.1 mM}, and between ΔS^≠_{pt,0.4 mM}, ΔS^≠_{pt,2 mM} and ΔS^≠_{sm,0.1 mM} correlate with the earlier finding that adsorption of HQ onto roughened Pt surfaces occurred primarily in the flat orientation at all concentrations studied.     

The formation and structural chemistry of the hexa(μ-t-butylthiolato) pentacuprate(I) cage anion with triethylammonium and tetraethylammonium cations

Yellow (Et₄N)[Cu₅(SBu^t)₆] crystallises from solutions prepared from Cu(II), Bu^tSH, Et₃N and Et₄NBr in acetone/ethanol, while (Et₃NH)[Cu₅(SBu^t)₆] crystallises from solutions of CuSBu^t and Bu^tSH in Et₃N. Crystal structure determinations reveal that both compounds contain the molecular cage [Cu₅(μ-SBu^t)₆]^?, in which two copper atoms are three-coordinate (Cu_trig), three copper atoms are two-coordinate (Cu_dig), and all thiolate ligands are doubly-bridging. The polyhedral stereochemistry of the core is trigonalbipyramido-Cu₅-trigonal antiprismo-S₆. The complete [Cu₅(μ-SBu^t)₆]^? cage in the Et₄N⁺ compound closely approaches D₃ symmetry, but in the Et₃NH⁺ compound one SBu^t ligand is inverted at the sulphur bridge, causing angular distortions in the cage.Two structural features, the antiprismatic twist of the S₆ polyhedron and the bending of Cu_dig towards the cage centroid (S-Cu_dig-S = 171(1)°), provide evidence for weak Cu-Cu attractive interactions within the cage. Infrared data are discussed. Crystal data: (Et₄N)[Cu₅(SBu^t)₆], C₃₂H₇₄Cu₅NS₆, a = 45.500 (3), b = 11.805(1), c = 20.168(2) Å, β = 117.81 (1)°, C2/c, Z = 8, R = 0.078 (2953 observed F); (Et₃NH)[Cu₅(SBu^t)₆], C₃₀H₇₀Cu₅NS₆, a = 10.519(1), b = 21.457(1), c = 20.065(1), β = 95.11(1), P2₁/c, Z = 4, R = 0.072 (3093 observed F). (Et₄N)[Ag₅(SBu^t)₆] is isostructural with (Et₄N)[Cu₅(SBu^t)₆].     

Cluster bonding and energetics of the borane anions,BnHn2− (n = 5–12): A comparative study using bond length—bond enthal

Cluster bond enthalpies, E_L(BB), and orders, n?(BB), for the structurally characterised closo anions, B_nH_n^2? (n = 6 and 8–12), have been estimated using the logarithmic length—enthalpy and enthalpy—order relationships E_L(BB) (kJ mol^?1) = 1.766 × 10¹¹ [L(BB)]^?4.0 and E_L(BB) (kJ mol^?1) = 318.8[n?(BB)]^0.697, respectively. In a parallel study, the molecular-orbital bond index CNDO-based calculation method has been used to give BB and BH bond indices, I(BB) and I(BH), from which bond index based bond enthalpies, E_I, have been calculated using the relationships E_I(BB) = 297.9 I(BB) and E_I(BH) = 374.8I(BH) (enthalpies in kJ mol^?1; lengths in pm). From these, total skeletal bond enthalpies Σ E(BB), and total bond enthalpies, Σ E(BB) + Σ E(BH), have been calculated. Although calculated values of E_L and Σ E_L generally exceed those of E_I and Σ E_I by some 8% and calculated values of I generally exceed those of n? by a greater amount, the trends in these parameters for the series of B_nH_n^2? anions are very similar, showing the greater efficiency with which the n + 1 skeletal electron pairs are used as n increases. However, the two approaches differ in that, whereas the Σ E_I values suggest that the anions are all of comparable stability, the ΣE_L values clearly show B₆H₆^2?, B₁₀H₁₀^2? and B₁₂H₁₂^2? to be more stable than B₈H₈^2?, B₉H₉^2? and B₁₁H₁₁^2?. The interatomic distances in B₇H₇^2? and in the unknown B₅ H₅^2? are estimated and used to assess their relative stabilities. The E_L values suggest that B₇ H₇^2? is of comparable stability to B₈H₈^2? etc., but show B₅H₅^2? as relatively unstable. The E_I values suggest that both of these anions should be relatively stable members of the series of closo anions.     

Analytical photoion spectroscopy applied to dissociative single and double photoionization of diatomic molecules (H2, N2, O2, CO,and NO)

This work reports the principle, advantage, and limitations of analytical photoion spectroscopy which has been applied to dissociative photoionization processes for diatomic molecules such as H₂, N₂, CO, and NO. Characteristic features observed in the differential photoion spectra are summarized with a focus on (pre)dissociation of(i) multielectron excitation states commonly observed in the inner valence regions,(ii) shape resonances, and(iii) doubly charged parent ions. Possible origins for negative peaks in the differential spectra are discussed. This spectroscopy is applied to the reported photoion branching ratios for D₂ (and H₂ at high energies). The main findings are as follows: (1) The direct dissociation of theX ²Σ _g ⁺ (1sσ _g ) state of D ₂ ⁺ , the two-electron excited state¹Σ _u ⁺ (2pσ _u 2sσ _g ) of D₂, and the²Σ _u ⁺ (2pσ _u ) state of D ₂ ⁺ appear clearly in the differential spectrum, as previously observed for H₂. (2) Decay of H ₂ ⁺ (D ₂ ⁺ ) to H⁺ (D⁺) above 38 eV is due to the direct dissociation of highly excited states of H ₂ ⁺ (D ₂ ⁺ ) such as the²Σ _g ⁺ (2sσ _g ) and high-lying Rydberg states converging on H ₂ ²⁺ (D ₂ ²⁺ ). (3) In the ionization continuum of H ₂ ²⁺ (D ₂ ²⁺ ) peculiar dissociation pathways are observed. The differential photoion spectra for O₂ derived from the reported photoion branching ratios are also presented. The (pre)dissociation of theb ⁴Σ _g ^? ,B ²Σ _g ^? , III²Π _u ,²Σ _u ^? , and^2,4Σ _g ^? states of O ₂ ⁺ appears as the corresponding positive values in the spectra in accord with previous observations. Some other dissociation pathways possibly contributing to the spectra are discussed including dissociative double ionization.     

Population and deactivation of lowest lying barium levels by collisions with He,Ar, Xe and Ba ground state atoms

Excitation transfer between the barium low lying excited states 6s6p ³ P ₁ ⁰ , 6s5d ¹ D ₂ and 6s5d ³ D _J by collisions with He,Ar,Xe and Ba has been investigated. The population densities in all levels involved were probed by absorption or by fluorescence usingcw lasers. The depopulation cross sections of the Ba³ P ₁ ⁰ state by collisions with noble gases were found to be σ_He(³ P ₁ ⁰ )=5.5·10^?16 cm², σ_Ar(³ P ₁ ⁰ )=4.6·10^?16 cm², and σ_Xe(³ P ₁ ⁰ )=1.7·10^?16 cm². For Ar, the collisional depopulation of the³ P ₁ ⁰ level is exclusively due to the transition to the¹ D ₂ state. Under the assumption that the³ D _J metastable states are populated collisionally by¹ D ₂ →³ D _J transfer only, we have deduced the upper limit for the corresponding cross section σ ₁₃ ^Ar =1.5·10^?18 cm². From the Ba¹ D ₂ and Ba³ D _J steady-state diffusion distributions, collisional relaxation rates of the¹ D ₂ and³ D _J levels were evaluated. The collisional relaxation rates by Ar and Ba yielded total cross sections for the depopulation of metastable levels: σ_Ar(¹ D ₂)=1.5·10^?17 cm², σ_Ba(¹ D ₂)?1·10^?13 cm², σ_Ar(³ D _J)=7·10^?21 cm², and σ_Ba(³ D _J)=1·10^?15 cm². Furthermore, it was found that the main contribution of the collisional depopulation of the¹ D ₂ state by Ar is related to back transfer to the³ P _J ⁰ state, whereas the deactivation of the³ D _J metastable state is due to back transfer to the¹ D ₂ state. Taking into account other cross sections reported in literature we can conclude that collisional deactivation of both metastable levels by Ba ground state atoms can be attributed to their mutual collisional mixing.     

Measurement of state-to-state rotational transfer rates in collision of I2*(B 0u+, υ = 15, j) with 3He, 4He,Ne, Ar,H2, D2 and I2

The selective laser excitation and induced fluorescence observation technique has been used to study rotationally inelastic collisions of I₂^*(B 0_u⁺, υ = 15,j) with I₂, ³He, ⁴He, Ne, Ar, H₂ and D₂. For each collision partner, several initial rotational levels ranging from j_i = 12 up to j_i = 146 have been excited. For purely rotational transfer within the υ = 15 level, our data are perfectly consistent with energy sudden (eventually corrected) scaling laws. Thus, any thermally averaged rate constant, k(j_i → j_f), can be expressed as a function of the basis rate constants k(l → 0). Furthermore, these k(l → 0) are found to follow simple empirical fitting laws. Consequently any k(j_i → j_f) can be predicted given a set of two or three fitting parameters. Collisions with relatively heavy particles (I₂, Ar and Ne) are well described by using the inverse power fitting law k(l → 0) = b[l(l+1)]^?γ, where b = 1.7, 1.2 and 1.2×10^?10 cm³ s^?1 and γ = 1.08, 1.02 and 1.17 for I₂^*-Ne, I₂^*-Ar and I₂^*-I₂ collisions respectively. For collisions with light particles (³He, ⁴He, H₂ and D₂), k(l → 0) shows a sharp decrease with l which can be accounted for by a hybrid power-exponential fitting law k(l → 0) = b[l(l+1)]^?γ exp[-l(l+1)/l^* (l^*+1)], where b = 0.84, 0.71, 2.77 and 2.78×10^?10 cm³ s^?1l⁺ = 20.6, 23.1, 18.8 and 31.4, and γ = 0.66, 0.66, 0.78 and 0.91 for I₂^*-³He, I₂^*-He, I₂^*-H₂ and I₂^*-D₂ collisions, respectively. We confirm that the rotational transfer dynamics in heavy molecules is mainly governed by angular momentum exchange.     

Rotational spectrum and molecular constants of the diatomic GaCl in its electronic ground state1ε+

At wavelengths near 1 mm six rotational transitions of GaCl have been observed. The analysis including previous measurements on the rotational transitionJ = 1 ← 0 resulted in extended sets of the Dunham parametersY ₀₁,Y ₁₁,Y ₂₁,Y ₃₁,Y ₀₂,Y ₁₂ andY ₀₃ of the four isotopic species⁶⁹Ga³⁵Cl,⁷¹Ga³⁵Cl,⁶⁹Ga³⁷Cl and⁷¹Ga³⁷Cl. With these microwave data the constantsY ₁₀ ≈ ε_e and —Y ₂₀ ≈ ω _e x _e were determined. The parameters of the Dunham potentiala ₀,a ₁,a ₂,a ₃ andr _e are given. The GaCl was produced by reaction of gaseous CCl₄ with Ga evaporated at 1,500°C.     

Fourier spectrometry investigation of the 1 3Σg+ →a 3Σu+ transition of the 7Li2 molecule

The 1 ³Σ_g⁺ → a ³Σ_u⁺ transition in the ⁷Li₂ molecule has been observed in the 8200–10 000 cm⁻¹ region with a high resolution Fourier spectrometer. Rotational analysis of 1 ⩽ υ′ ⩽ 7 of 1 ³Σ_g⁺ and 0 ⩽ υ″ ⩽ 7 of a ³Σ_u⁺ has been carried out. We found D_e(a ³Σ_u⁺) = 332.5 ± 1.0 cm⁻¹ that gives T_e(a ³Σ_u⁺) = 8184.3 ± 1.5 cm⁻¹ and D_e(1 ³Σ_g⁺) = 7090.4 ± 1.5 cm⁻¹ with T_e = 16330 ± 2 cm⁻¹.     

The absorption spectrum of carbon monoxide in the CO(3Π r,a) state between 215 nm and 285 nm

Bye-beam excitation of a He/CO mixture the CO(³Π _r ,a) state was sufficiently populated to allow the measurement of the absorption spectrum. The (0, 0), (1, 1), (2, 2) and (0, 1) bands of thec ³Π←a ³Π system of CO have been observed and the molecular constantsT _e =92036.0 cm^?1 (for the band head), ω _e =2249.5 cm^?1, ω _e x _e =29.5 cm^?1 have been derived for CO(c). A new electronic state withT _e =91854.3 cm^?1, ω _e =848.4 cm^?1, ω _e x _e =9.8 cm^?1,B _e =1.351 cm^?1, and α _e =0.021 cm^?1 was identified to be a³Σ state. It seems to be very likely that this state is the CO (3pσ,³Σ,j) state discussed in the literature. The results indicate a perturbation of the υ=1 levels of the new state by the CO (c,υ=0) levels. Another strong perturbation is found in the υ=4 levels. The three CO(³Σ,b,υ′=0,1,2)←CO (a,υ″=0) bands were also investigated yielding for CO(b):T _e =83778 cm^?1, ω _e =2335 cm^?1, ω _e x _e =59 cm^?1 andB _e =1.86 cm^?1.     

The polarizability of a pair of hydrogen atoms at long range

The coefficients of R^?6 and R^?9 in the long-range expansion of the parallel and perpendicular components of the polarizability of a pair of hydrogen atoms at a separation R have been calculated. The results are A⁽⁶⁾₆ = 2558.59. A⁽⁶⁾_⊥ = 1268.25, A⁽⁸⁾₆ = 90639.5 and A⁽⁸⁾_⊥ = 22010.3 au. The values of A⁽⁶⁾₆ and A⁽⁶⁾₆ and A⁽⁶⁾_| are somewhat larger than previous theoretical estimates and much larger than the classical values of 729 and 182.25 au. The terms in R^?8 arise from distortion associated with the dispersion forces and from the field of the quadrupole moment induced by the field-gradient at each atom.