The adsorption of CO,H2, H2, CO2 and H2O on carburized and graphitized Ni(110)

A study of the adsorption/desorption behavior of CO, H₂O, CO₂ and H₂ on Ni(110)(4 × 5)-C and Ni(110)-graphite was made in order to assess the importance of desorption as a rate-limiting step for the decomposition of formic acid and to identify available reaction channels for the decomposition. The carbide surface adsorbed CO and H₂O in amounts comparable to the clean surface, whereas this surface, unlike clean Ni(110), did not appreciably adsorb H₂. The binding energy of CO on the carbide was coverage sensitive, decreasing from 21 to 12 $\text{kcal}\text{mol}$ as the CO coverage approached 1.1 × 10¹⁵ molecules cm^?2 at 200K. The initial sticking probability and maximum coverage of CO on the carbide surface were close to that observed for clean Ni(110). The amount of H₂, CO, CO₂ and H₂O adsorbed on the graphitized surface was insignificant relative to the clean surface. The kinetics of adsorption/desorption of the states observed are discussed.     

Chemical shifts in auger electron spectra from silicon in silicon nitride

The chemisorption of nitric oxide on (110) nickel has been investigated by Auger electron spectroscopy, LEED and thermal desorption. The NO adsorbed irreversibly at 300 K and a faint (2 × 3) structure was observed. At 500 K this pattern intensified, the nitrogen Auger signal increased and the oxygen signal decreased. This is interpreted as the dissociation of NO which had been bound via nitrogen to the surface. By measuring the rate of the decomposition as a function of temperature the dissociation energy is calculated at 125 kJ mol^?1. At ～860 K nitrogen desorbs. The rate of this desorption has been measured by AES and by quantitative thermal desorption. It is shown that the desorption of N₂ is first order and that the binding energy is 213 kJ mol^?1. The small increase in desorption temperature with increasing coverage is interpreted as due to an attractive interaction between adsorbed molecules of ～14 kJ mol^?1 for a monolayer. The (2 × 3) LEED pattern which persists from 500–800 K is shown to be associated with nitrogen only. The same pattern is obtained on a carbon contaminated crystal from which oxygen has desorbed as CO and CO₂. The (2 × 3) pattern has spots split along the (0.1) direction as $\text{(m,}\text{n}\text{3}\text{)}$ and $\text{(}\text{m}\text{2, n}\text{)}$. This is interpreted as domains of (2 × 3) structures separated by boundaries which give phase differences of $\text{2π}\text{3}$ and π. The split spots coalesce as the nitrogen starts to desorb. A (2 × 1) pattern due to adsorbed oxygen was then observed to 1100 K when the oxygen dissolved in the crystal leaving the nickel (110) pattern.     

Lattice gas model for O on Ni(110)

We consider the unusual behavior of the chemisorption system O on Ni(110). At a coverage of about$\text{1}\text{3}$, as the temperature is increased from room temperature to about 300°C, a wellordered (3 × 1) structure changes reversibly into a poorly organized (2 × 1) structure. This has been observed for a Ni crystal saturated with oxygen in the interior. We propose a two-dimensional lattice gas model with anisotropic and competing interactions between the adsorbed atoms to explain this behavior. Monte Carlo calculations on a 30 × 30 lattice show a transition of this type for coverages near$\text{1}\text{3}$.     

Adsorption of oxygen on Pt(111)

Oxygen adsorbed on Pt(111) has been studied by means of temperature programmed thermal desorption spectroscopy (TPDS). high resolution electron energy loss spectroscopy (EELS) and LEED. At about 100 K oxygen is found to be adsorbed in a molecular form with the axis of the molecule parallel to the surface as a peroxo-like species, that is, the OO bond order is about 1. At saturation coverage (θ_mol= 0.44) a $\text{(}\text{3}\text{2}\text{×}\text{3}\text{2}\text{)R15°}$ diffraction pattern is observed. The sticking probability S at 100 K as a function of coverage passes through a maximum at θ = 0.11 with S = 0.68. The shape of the coverage dependence is characteristic for adsorption in islands. Two coexisting types of adsorbed oxygen molecules with different OO stretching vibrations are distinguished. At higher coverages units with v-OO = 875 cm^?1 are dominant. With decreasing oxygen coverages the concentration of a type with v-OO = 700 cm^?1 is increased. The dissociation energy of the OO bond in the speices with v-OO = 875 cm^?1 is estimated from the frequency shift of the first overtone to be ~ 0.5 eV. When the sample is annealed oxygen partially desorbs at ~ 160K, partially dissociates and orders into a p(2×2) overlayer. Below saturation coverage of molecular oxygen, dissociation takes place already at92 K. Atomically adsorbed oxygen occupies threefold hollow sites, with a fundamental stretching frequency of 480 cm^?1. In the non-fundamental spectrum of atomic oxygen the overtone of the E-type vibration is observed, which is “dipole forbidden” as a fundamental in EELS.     

Trapping probabilities and desorption energies of alkali atoms on a clean and an oxygen covered tungsten (110) surface

Alkali atoms were scattered with hyperthermal energies from a clean and an oxygen covered (θ ≈ 0.5 ML) W(110) surface. The trapping probability of K and Na atoms on oxygen covered W(110) has been measured as a function of incoming energy (0–30 eV) and incident angle. A considerable enhancement of trapping on the oxygen covered surface compared to a clean surface was observed. At energies above 25 eV there are still K and Na atoms being trapped by the oxygen covered surface. From the temperature dependence of the mean residence time τ of the initially trapped atoms the pre-exponential factor τ₀ and the desorption energy Q were derived using the relation: $\text{τ = τ}{}_0\text{exp}\text{(}\text{Q}\text{kT}{}_{\mathrm{<mtext>s</mtext>}}\text{)}$. On clean W(110) we obtained for Li: $\text{τ}{}_0\text{= (8 ±}\text{8}\text{4}\text{) × 10}{}^{\mathrm{?14}}\text{sec}$, Q = (2.78 ± 0.09) eV; for Na: τ₀ = (9 ± 3) × 10^?14 sec, Q = (2.55 ± 0.04) eV; and for K: τ₀ = (4 ± 1) × 10^?13 sec, Q = (2.05 ± 0.02) eV. Oxygen covered W(110) gave for Na: τ₀ = (7 ±3) × 10^?15 sec, Q = (2.88 ± 0.05) eV; and for K: $\text{τ}{}_0\text{= (1.3 ±}\text{0.9}\text{0.6}\text{) × 10}{}^{\mathrm{?14}}\text{sec}$, Q = (2.48 ±0.05) eV. The adsorption on clean W(110) has the features of a supermobile two-dimentional gas; on the oxygen covered W(110) adsorbed atoms have the partition function of a one-dimen-sional gas. The binding of the adatoms to the surface has a highly ionic character in the systems of the present experiment. An estimate is given for the screening length of the non-perfect conductor W(110):k_s^?1≈ 0.5 Å.     

The interaction of oxygen with the Rh(111) surface a

The adsorption of oxygen on Rh(111) at 100 K has been studied by TDS, AES, and LEED. Oxygen adsorbs in a disordered state at 100 K and orders irreversibly into an apparent (2 × 2) surface structure upon heating to T? 150 K. The kinetics of this ordering process have been measured by monitoring the intensity of the oxygen $\text{(1,}\text{1}\text{2}\text{) LEED}$ beam as a function of time with a Faraday cup collector. The kinetic data fit a model in which the rate of ordering of oxygen atoms is proportional to the square of the concentration of disordered species due to the nature of adparticle interactions in building up an island structure. The activation energy for ordering is $\text{13.5 ± 0.5}\text{kcal}\text{mole}$. At higher temperatures, the oxygen undergoes a two-step irreversible disordering (T? 280 K) and dissolution (T?400K) process. Formation of the high temperature disordered state is impeded at high oxygen coverages. Analysis of the oxygen thermal desorption data, assuming second order desorption kinetics, yields values of 56 ± 2 kcal/ mole and 2.5 ± 10^?3 cm² s^?1 for the activation energy of desorption and the pre-exponential factor of the desorption rate coefficient, respectively, in the limit of zero coverage. At non-zero coverages the desorption data are complicated by contributions from multiple states. A value for the initial sticking probability of 0.2 was determined from Auger data at 100 K applying a mobile precursor model of adsorption.     

Interactions of CO molecules adsorbed on oxidised Cu(111) and Cu(110)

Reflection absorption infrared spectroscopy has been used in conjunction with LEED and surface potential measurements to study low temperature CO adsorption on the oxidised Cu surfaces Cu(111)O|$\text{3}\text{2}\text{?}\text{2}$|, Cu(110)O(2 × 1) and Cu(110)Oc(6 × 2). On all three surfaces adsorption at 80 K yields surface potential changes in excess of 0.6 V and does not lead to the formation of an ordered overlayer. At high coverages the adsorption enthalpy is lower than on the clean surfaces. Infrared spectra show the growth of a doublet band with components initially at 2100 and 2117 cm^?1 on the oxidised Cu(111) surface. Similar features seen on the oxidised Cu(110) surfaces are accompanied by a band at 2140 cm^?1: a very weak band at the same frequency on oxidised Cu(111) is attributed to defect sites. Studies of the temperature dependence of the spectrum from oxidised Cu(111) lead to the conclusion that two different binding sites are occupied. Spectra of ${}^{12}\text{CO}{}^{13}\text{CO}$ mixtures show that the molecules occupying these sites are in close proximity to each other, and that the spectrum is subject to large but opposing coverage-dependent frequency shifts.     

A leed and AES study of the adsorption of chlorine on W(100) at room temperature

The surface structures formed on room temperature adsorption of chlorine on W(100) and subsequent annealing of the saturated surface have been characterised by LEED. The progress of gas adsorption was followed by AES which was also used to observe relative chlorine coverage on annealing. Room temperature adsorption was random up to the saturation exposure of 1.7 L. On annealing the chlorine adlayer ordering commenced at about 800 K. One-dimensional ordering into rows along the <1, 1> directions was followed by the ordering of these into two 2D structures: an interpenetrating $\text{7}\text{1}\text{1}\text{1}$ at 830 K and an interpenetrating $\text{5}\text{1}\text{6}\text{1}$ for 860 K and above. Desorption started after 1050 K annealing and was complete by 1440 K. Saturation chlorine coverage is inferred as 5 × 10¹⁴ atoms cm^?2 and the single desorption peak coupled with the LEED analysis suggests that chlorine is bridge bonded to the W(100) surface for the ordered overlayer.     

The GaP(001) surface and the adsorption of Cs

GaP(001) cleaned by argon-ion bombardment and annealed at 500°C showed the Ga-stabilized GaP(001)(4 × 2) structure. Only treatment in 10^?5 Torr PH₃ at 500°C gave the P-stabilized GaP(001)(1 × 2) structure. The AES peak ratio $\text{P}\text{Ga}$ is 2 for the (4 × 2) and 3.5 for the (1 × 2) structure. Cs adsorbs with a sticking probability of unity up to 5 × 10¹⁴ Cs atoms cm^?2 and a lower one at higher coverages. The photoemission measured with uv light of 3660 Å showed a maximum at the coverage of 5 × 10¹⁴ atoms cm^?2. Cs adsorbs amorphously at room temperature, but heat treatment gives ordered structures, which are thought to be reconstructed GaP(001) structures induced by Cs. The LEED patterns showed the GaP(001)(1 × 2) Cs structure formed at 180°C for 10 h with a Cs coverage of 5 × 10¹⁴ atoms cm^?2, the GaP(001)(1 × 4) Cs formed at 210°C for 10 hours with a Cs coverage of 2.7 × 10¹⁴ atoms cm^?2, the GaP(001)(7 × 1) and the high temperature GaP(001)(1 × 4), the latter two with very low Cs content. Desorption measurements show three stability regions: (a) between 25–150°C for coverages greater than 5 × 10¹⁴ atoms cm^?2, and an activation energy of 1.2 eV; (b) between 180–200°C with a coverage of 5 × 10¹⁴ atoms cm^?2, and an activation energy of 1.8 eV; (c) between 210–400°C with a coverage of 2.7 × 10¹⁴ atoms cm^?2, and an activation energy of 2.5 eV.     

Structure of the Ag on Si(111) 7 × 7 interface by means of surface exafs

Polarization dependent surface extended X-ray absorption fine structure (SEXAFS) measurements are used to determine the structure of the Ag on Si(111)7 × 7 system at the early stages (< 3 monolayers (ML)) of interface formation. At room temperature (RT) Ag is found to initially (< 0.5 ML) chemisorb in the threefold hollow site, approximately 0.7 Å above the outermost Si layer with an average Ag-Si distance of 2.48±0.05 Å. Above monolayer coverage the SEXAFS spectrum is dominated by the Ag-Ag distance indicating Ag island formation on the surface. Upon heating (200 ?T? 600°C) a (√3 ×√3)R30° LEED pattern is observed. At the lowest coverage ( < 0.7 ML) this pattern is determined to arise from Ag atoms which are embedded in the threefold hollows, ~ 0.7 Å below the first and above the second Si layer, with a Ag-Si distance of 2.48 ± 0.04 Å. At higher coverage ($\text{\$}\text{?}$1 ML) Ag clusters are found to grow on this interface with the same Ag-Ag distance as in Ag metal. Our results are discussed in the context of previous experimental and theoretical results.     

Temperature jump method in molecular beam relaxation spectrometry applied to catalytic decomposition of CH3OH on polycrystalline Ni foil

A new modification of molecular beam relaxation spectrometry (MBRS) is described: the temperature jump method for studying catalytic surface processes on metal foils. The temperature of the catalyst foil is maintained by direct ohmic heating; a constant particle beam is directed towards the catalyst surface. A jump of the surface temperature caused by a high current pulse generates a response of the fluxes of desorption. The decay of the desorption intensity after the temperature jump contains the relaxation times of the elementary steps involved. The mathematical treatments of unimolecular and bimolecular surface reactions, of sequences of two and three unimolecular steps and of a sequential reaction accompanied by the redesorption of the reactant are given. The application of the new method is shown by a study of the catalytic decomposition of CH₃)OH on polycrystalline Ni: CO and H₂ are the sole reaction products. The limit of the catalytic activity — apart from the low sticking probability of the reactant — must be seen in the abstraction of the first methyl hydrogen from the transient methoxy species. In the temperature range between 320 and 550 K the reaction mechanism can be described as follows:

Rate constants in dependence from surface temperature T are: k₁ = 4.2 × 10⁴ exp$\text{(}\text{?22.4}\text{RT}$$\text{kJ}\text{mol}\text{)}$ s^?1; k₃ = 2.4 × 10⁹ exp$\text{(}\text{?75}\text{RT}$$\text{kJ}\text{mol}\text{)}$ s^?1; k₄ = 1.2 × 10¹³ exp$\text{(}\text{?104}\text{RT}$$\text{kJ}\text{mol}\text{)}$ s^?1; η = 0.2. Typical surface residence times of the intermediates are: 110 ? τ₁ ? 15 ms at 320 ? T ? 450 K; 210 ? τ₃ ? 6 ms at 450 ? T ? 550 K; 98 ? τ₄ ? 6 ms at 450 ? T ? 500 K.     

Displacive surface phases formed by hydrogen chemisorption on W {001}

A detailed LEED study is reported of the surface phases stabilised by hydrogen chemisorption on W {001}, over the temperature range 170 to 400 K, correlated with absolute determinations of surface coverages and sticking probabilities. The saturation coverage at 300 K is 19(± 3) × 10¹⁴ atoms cm^?2, corresponding to a surface stoichiometry of WH₂, and the initial sticking probability for both H₂ and D₂ is 0.60 ± 0.03, independent of substrate temperature down to 170 K. Over the range 170 to 300 K six coverage-dependent temperature-independent phases are identified, and the transition coverages determined. As with the clean surface $\text{(}\text{2}\text{×}\text{2}\text{)R45°}$ displacive phase, the c(2 × 2)-H phase is inhibited by the presence of steps and impurities over large distances (～20 Å), again strongly indicative of CDW-PLD mechanisms for the formation of the H-stabilised phases. These phases are significantly more temperature stable than the clean $\text{(}\text{2}\text{×}\text{2}\text{)R45°}$, the most stable being a c(2 × 2)-H split half-order phase which is formed at domain stoichiometries between WH_0.3 and WH_0.5. LEED symmetry analysis, the dependence of half-order intensity and half-width on coverage, and I-V spectra indicate that the c(2 × 2)-H phase is a different displacive structure from that determined by Debe and King for the clean $\text{(}\text{2}\text{×}\text{2}\text{)R45°}$. LEED I-V spectra are consistent with an expansion of the surface-bulk interlayer spacing from 1.48 to 1.51 Å as the hydrogen coverage increases to ～4 × 10¹⁴ atoms cm^?2. The transition from the split half-order to a streaked half-order phase is found to be correlated with changes in a range of other physical properties previously reported for this system. As the surface stoichiometry increases from WH to WH₂ a gradual transition occurs between a phase devoid of long-range order to well-ordered (1 × 1)-H. Displacive structures are proposed for the various phases formed, based on the hypothesis that at any coverage the most stable phase is determined by the gain in stability produced by a combination of chemical bonding to form a local surface complex and electron-phonon coupling to produce a periodic lattice distortion. The sequence of commensurate, incommensurate and disordered structures are consistent with the wealth of data now available for this system. Finally, a simple structural model is suggested for the peak-splitting observed in desorption spectra.     

Interaction of inert gases with a nickel (100) surface: I. Adsorption of xenon

The adsorption of Xe on a Ni(100) surface has been studied in UHV between 30 and 100 K using LEED, thermal desorption spectroscopy (TDS), work function (Δφ) measurements, and UV photoemission (UPS). At and below 80 K, Xe adsorbs readily with high initial sticking probability and via precursor state adsorption kinetics to form a partially ordered phase. This phase has a binding energy of ~5.2 kcal/mole as determined by isosteric heat measurements. The heat of adsorption is fairly constant up to medium coverages and then drops continuously as the coverage increases, indicating repulsive mutual interactions. The thermal desorption is first order with a preexponential factor of about 10¹² s^?1, indicative of completely mobile adsorption. Adsorbed Xe lowers the work function of the Ni surface by 376 mV at monolayer coverage. (This coverage is determined from LEED to be 5.65 × 10¹⁴ Xe molecules/cm^-2.) For not too high coverages, θ, Δφ(θ) can be described by the Topping model, with the initial dipole moment μ₀ = 0.29 D and the polarizability α being 3.5 × 10^?24 cm³. In photoemission, the $\text{Xe 5p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and $\text{5p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ orbitals show up as intense peaks at 5.56 and 6.83 eV below E_f which do not shift their position as the coverage varies. Multilayer adsorption (i.e. the filling of the second and third layers) can be seen by TDS. The binding energies of these α states can be estimated to range between 4.5 and 3.5 kcal/mole. The results are compared and contrasted with previous findings of Xe adsorption on other transition metal surfaces and are discussed with respect to the nature of the inert-gas-metal adsorptive bond.     

AES measurements of adsorption isobars for oxygen on tungsten at low pressure and high temperature

Auger electron spectroscopy (AES) has been employed to determine the relative coverage of oxygen on polycrystalline tungsten at high temperatures (1200 ?T ? 2500 K) and low O₂ pressures (5 × 10^?9 ?po₂ ?5 × 10^?6 Torr). We believe that this is the first demonstration that chemical analysis of solid surfaces by AES is possible even at temperatures as high as 2500 K. It is assumed that the relative oxygen coverage is directly proportional to the peak-to-peak amplitude of the first derivative of the 509 eV oxygen Auger peak. The experimental results illustrate the dependence of coverage on temperature and pressure, and it is shown that the results for low coverages may be described reasonably well by a simple first-order desorption model plus a semi-empirical expression for the equilibration probability (or sticking coefficient). On the basis of this approximate model, the binding energy of oxygen on tungsten is estimated as a function of coverage, giving a value of ～ 140 $\text{kcal}\text{mole}$ in the limit of zero coverage.     

Co desorption and adsorption on Pt(111)

The kinetics of the desorption of CO from a Pt(111) crystal between 419 and 505 K is reported using a Low-Energy Molecular-Beam-Scattering (LEMS) technique with a helium probe beam and a CO dosing beam. The resulting first-order Arrhenius rate constant is $\text{k = 2.7 × 10}{}^{13}\text{exp(?31.1}\text{kcal}\text{mole}\text{· RT) s}{}^{\mathrm{?1}}$. We also report a study of the equilibriumadsorbed CO between 400 and 600 K using LEMS. These results, fitted to a Temkin isotherm model, indicate that the adsorption energy decreases linearly with surface coverage with the average value equal to $\text{31.1 + 1.2}\text{kcal}\text{mole}$ over the coverage range 0 < θ ? 0.5. The average harmonic oscillator frequency of the adsorbed CO molecules is 191 ± 76 cm^?1.     

The adsorption of acetylene on W(100) at room temperature: An electron spectroscopic study

The adsorption of acetylene on W(100) at room temperature has been studied by AES, ELS, thermal desorption, mass spectrometry, work function and LEED in one vacuum chamber. AES line profile analysis shows that there are at least two adsorption processes occurring at room temperature. Further, it is possible to explain all the AES results by assuming non-sequential adsorption into just two states, denoted by α and β. This picture was substantiated and embellished by comparison with other standard surface techniques. The α-state comprises either a C₂H₂ unit with an activation energy for desorption of $\text{2.3}\text{eV}\text{molecule}\text{(53}\text{kcal mole}{}^{\mathrm{?1}}\text{)}$ or CH units bounded through the carbon of the β-state. Saturation coverage for the α-state is 3 × 10¹⁴ molecules cm^?2. The β-state is dissociative at low acetylene exposures and comparison between a carbon covered surface and the β-state suggest the latter to be dissociative up to saturation. There also appears to be ca. 10¹⁴ hydrogen atoms cm^?2 on W(100) on room temperature acetylene saturation, the carbon content of the β-state being 9 × 10¹⁴ atoms cm^?2. The residual C?C bond from the molecule in the β-state remains unknown. No sign of ordering in the adsorbed species was detected, save the possibility of (1 × 1) in the β-state. Acetylene adsorption at 580 K showed hydrogen from the β-state to block acetylene adsorption by 15% at saturation. A two-site adsorption model for the β-state is proposed to explain the results. The α-state is bonded through the carbon of the β-state and it is speculated that the former adsorbs onto “β” domains where there is a critical minimum size for the latter.     

Electrical transport and magnetic properties of Nd2(WO4)3

Measurements of the molar magnetic susceptibility (X_m) of a powdered sample of Nd₂(WO₄)₃ in the temperature range 300–900 K, and the electrical conductivity (σ) and dielectric constant (?$\text{)}\text{?}$ of pressed pellets of the compound in the temperature range 4.2–1180 K are reported. X_m obeys the Curie-Weiss law with a Curie constant C= 3.13 K/mole, a paramagnetic Curie temperature θ= ?60 K and a moment of Bohr magnetons, p= 3.49 for the Nd³⁺ ion. The electrical conductivity data can be explained in terms of the usual band model and impurity levels. Both the σ and ?$\text{\$}\text{?}$data indicate some sort of phase transition round 1025 K. The conductivity follows Mott's law $\text{σ = A exp (?B/T}{}^{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{)}$ in the temperature range $\text{200 < T < 3000}\text{K with}\text{B = 45.00 (}\text{K}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{and}\text{A = 1.38 × 10}{}^{\mathrm{?5}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$. The dielectric constant increases slowly up to 600 K, as is usual for ionic solids. The increase becomes much faster above 600 K, which is attributed to space-charge polarization of thermally generated charge carriers.     

A LEED study of adsorbed neon on graphite

Neon monolayers on graphite have been investigated by high resolution LEED in the range 14.5 < T < 7.5 K and 10^?8 < p < 10^?4 Torr. The fluid-solid transition line has the form ln$\text{(}\text{p}\text{Torr}\text{)= ?}\text{A}\text{T + B}\text{,}\text{with}\text{A = 740 ± 45}\text{K and}\text{B = 31.0 ± 2.8}$. The solid is an incommensurate rotated phase whose lattice parameter decreases and rotation angle increases away from the transition line. Comparison is made with other thermodynamic and diffraction studies, and a preliminary phase diagram is constructed. Extrapolation of these data to higher temperatures and pressure suggests that this rotated solid monolayer is stable up to 23–25 K (P = 3?10 Torr) at coverage x = 1, and is stable over the range 0.88 < x < 1.0 at T = 16 K (2 × 10^?7 < p 1.5 × 10^?2 Torr). Extrapolation to lower temperatures gives the 2D triple point pressure in the range p = (0.3?3) × 10^?10 Torr. The steep slope of the fluid-solid transition line is consistent with the fluid phase having a high density (x?0.80) in the temperature range studied.     

Microwave spectral study of 2-fluorophenol: cis conformer

The microwave spectra of 2-fluorophenol and its deuterated species have been observed and analyzed in the frequency ranges 12.5–18.0 GHz (KU band) and 21.5–26.0 GHz (K band) in the ground vibrational state at room temperature. For the normal species, the radio frequency-microwave double resonance spectrum has been recorded in the frequency range 30.0–38.0 GHz. Three rotational and five quartic centrifugal distortion constants for the normal species, $\text{A}\text{?}\text{= 3337.86 ± 0.02}$, $\text{B}\text{?}\text{= 2231.92 ± 0.01}$, $\text{C}\text{?}\text{= 1337.52 ± 0.01}$, d_J = (3.5 ± 2.9) × 10^?4, d_JK = (?4.9 ± 1.5) × 10^?3, d_K = (?3.2 ± 1.0) × 10^?3, d_WJ = (?2.0 ± 1.0) × 10^?7, d_WK = (2.6 ± 0.8) × 10^?6 (in MHz), and three rotational constants for the deuterated species, $\text{A}\text{?}\text{= 3324.70 ± 0.03}$, $\text{B}\text{?}\text{= 2177.95 ± 0.03}$, $\text{C}\text{?}\text{= 1315.96 ± 0.03}$ (in MHz), have been obtained. Consideration of the r_s coordinate of the hydroxyl hydrogen atom leads to the assignment of the spectra to the cis conformer of the molecule. An r₀ structure for the cis conformer has been proposed. The nonbonded OH ? F distance is lower by about 0.3 Å than the sum of the van der Waals radii.