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Ambient temperature static high pressure compression of liquid nitroethane has been performed using the diamond anvil technique. The first transition to a crystalline powder around 4.2 GPa did not return reliable indexing solutions and could be the result of a mixture of phases. Subsequent cycling of the pressure apparatus with the same sample triggered a solid-solid transition around 4.9-4.3 GPa on the downstroke. Indexing returned a monoclinic structure with spacegroup P21 or P21/m which is consistent with the lowest enthalpy solution predicted from density functional theory (DFT) calculations performed in this study, namely, P21. Attempts to reproduce the first anomalous mixture of phases with other samples were not successful; rather, the numerically preferred monoclinic structure manifests itself after a liquid-solid transition around 4.3-3.6 GPa, a value consistent with the results of a previous study. The transition typically occurs more readily on the downstroke. Incomplete Debye rings resulting from preferred orientation complicates any Rietveld refinement, though the DFT simulations predict 2 molecules per unit cell. Unit cell volumes during the upstroke were within 3% of that predicted by DFT calculations. This departure increases to about 9% below that from DFT predictions during the downstroke suggesting the presence of residual stresses due to non-hydrostatic conditions. Finally, a sudden relief in d-spacing values around 3.7-4.3 GPa during the downstroke is thought to be due to the influence of intermolecular hydrogen bonding.

Dissociative electron attachment (DEA) to nitroethane (C2H5NO2) in the gas phase is studied using a crossed electron–molecule beams technique. The ion yields for particular fragment ions were measured in the electron energy range from 0 to 9.5 eV with an electron energy resolution of about 120 meV. In contrast to previous studies additional negative ions, i.e., HCN− and NO−, were observed. Measures for the absolute partial cross sections were obtained for the ions using a calibration technique involving a comparison with the known cross section of the 0.8 eV peak in DEA to CCl4. The dominant negative ion product is NO2− with a cross section of approximately 11×10−22 m2 at 0.75 eV. The values of the cross section estimates for the other ions are about σ(C2H3NO2−)=4×10−24 m2 at ∼0 eV, σ(O−)=5×10−24 m2 at 5.7 eV, σ(OH−)=2×10−24 m2 at 5.7 eV, σ(CN−)=5×10−25 m2 at 1.7 eV, σ(CNO−)=3×10−25 m2 at ∼4.5 eV, σ(HCN−)=2×10−25 m2 at ∼4.5 eV and σ(NO−)=3×10−25 m2 at ∼8 eV.

Nitromethane has been studied as a model of energetic alphatic nitro compounds. The initiation of the decomposition mechanism of nitromethane in the vicinity of its explosive decomposition pressure conditions has been studied under high static pressure at ambient temperature by Raman spectroscopy. The vibrational modes νa(NO2) and, to a lesser degree, νs(NO2) show a specific behavior at the solid (II)–solid (III) 7.5 GPa transition (at ambient temperature). A comparison of the Raman spectrum of nitromethane-h3 with new high pressure Raman spectroscopic results for nitromethane-d3 and nitroethane allows one to characterize the physico chemical behavior of these three compounds in relation to their detonic properties.

We present low-energy velocity map photoelectron imaging results for bare and Ar solvated nitroethane anions. We report an improved value for the adiabatic electron affinity of nitroethane of (191 ± 6) meV which is used to obtain a C-NO(2) bond dissociation energy of (0.589 ± 0.019) eV in nitroethane anion. We assign a weak feature at (27 ± 5) meV electron binding energy to the dipole-bound anion state of nitroethane. Photoelectron angular distributions exhibit increasing anisotropy with increasing kinetic energies. The main contributions to the photoelectron spectrum of nitroethane anion can be assigned to the vibrational modes of the nitro group. Transitions involving torsional motion around the CN bond axis lead to strong spectral congestion. Interpretation of the photoelectron spectrum is assisted by ab initio calculations and Franck-Condon simulations.

The critical system 3-methylpentane-nitroethane-cyclohexane (3-MP-NE-CH) has been investigated and compared to the limiting binary systems 3-MP-NE as well as NE-CH in order to study the degree of renormalization in the critical exponents of the ternary system. The solubility curves of the 3-MP-NE-CH system have been determined at various molar ratios of the nonpolar constituents in order to obtain the plait points as a function of mixture composition. At the col point (the mixture with the lowest transition temperature) and two further plait point compositions shear viscosity, dynamic light scattering, and frequency-dependent ultrasonic attenuation coefficient measurements have been performed as a function of temperature near the critical temperatures. The fluctuation correlation length and the relaxation rate of fluctuations display power law behavior as a function of reduced temperature, with universal critical exponents nu = 0.63 and nuZ(0) = 1.928, respectively, as characteristic for binary critical mixtures. In conformity with the 3-MP-NE and NE-CH critical mixtures the scaling function in the ultrasonic spectra nicely agrees with the empirical scaling function of the Bhattacharjee-Ferrell dynamic scaling theory. Hence with respect to power laws and scaling the 3-MP-NE-CH system behaves like a quasibinary mixture. The individual amplitudes of the relaxation rate show a minimum at the col point composition, corresponding with a maximum in the background viscosity of the liquids. The amount of the adiabatic coupling constant g, derived from the amplitudes in the ultrasonic spectra, increases monotonously when going from NE-CH (/g/ = 0.1) to 3-MP-NE (/g/ = 0.26).

Valence and dipole-bound negative ions of the nitroethane (NE) molecule and its clusters are studied using photoelectron spectroscopy (PES), Rydberg electron transfer (RET) techniques, and ab initio methods. Valence adiabatic electron affinities (EA(a)s) of NE, C(2)H(5)NO(2), and its clusters, (C(2)H(5)NO(2))(n), n=2-5, are estimated using vibrationally unresolved PES to be 0.3+/-0.2 eV (n=1), 0.9+/-0.2 eV (n=2), 1.5+/-0.2 eV (n=3), 1.9+/-0.2 eV (n=4), and 2.1+/-0.2 eV (n=5). These energies were then used to determine stepwise anion-neutral solvation energies and compared with previous literature values. Vertical detachment energies for (C(2)H(5)NO(2))(n)(-) were also measured to be 0.92+/-0.10 eV (n=1), 1.63+/-0.10 eV (n=2), 2.04+/-0.10 eV (n=3), and 2.3+/-0.1 eV (n=4). RET experiments show that Rydberg electrons can be attached to NE both as dipole-bound and valence bound anion states. The results are similar to those found for nitromethane (NM), where it was argued that the diffuse dipole state act as a "doorway state" to the more tightly bound valence anion. Using previous models for relating the maximum in the RET dependence of the Rydberg effective principle number n(max)(*), the dipole-bound electron affinity is predicted to be approximately 25 meV. However, a close examination of the RET cross section data for NE and a re-examination of such data for NM finds a much broader dependence on n(*) than is seen for RET in conventional dipole bound states and, more importantly, a pronounced [l] dependence is found in n(max)(*) (n(max)(*) increases with [l]). Ab initio calculations agree well with the experimental results apart from the vertical electron affinity value associated with the dipole bound state which is predicted to be 8 meV. Moreover, the calculations help to visualize the dramatic difference in the distributions of the excess electron for dipole-bound and valence states, and suggest that NE clusters form only anions where the excess electron localizes on a single monomer.

The frozen natural orbital (FNO) coupled-cluster method increases the speed of coupled-cluster (CC) calculations by an order of magnitude with no consequential error along a potential energy surface. This method allows the virtual space of a correlated calculation to be reduced by about half, significantly reducing the time spent performing the coupled-cluster (CC) calculation. This paper reports the derivation and implementation of analytical gradients for FNO-CC, including all orbital relaxation for both noncanonical and semicanonical perturbed orbitals. These derivatives introduce several new orbital relaxation contributions to the CC density matrices. FNO-CCSD(T) and FNO-LambdaCCSD(T) are applied to a test set of equilibrium structures, verifying that these methods are capable of reproducing geometries and vibrational frequencies accurately, as well as energies. Several decomposition pathways of nitroethane are investigated using CCSD(T) and LambdaCCSD(T) with 60% of the FNO virtual orbitals in a cc-pVTZ basis, and find differences on the order of 5 kcalmol with reordering of the transition state energies when compared to B3LYP 6-311 + G(3df, 2p).

The behavior of polyethylene oxide (PEO, molecular weight, M(w) = 9 x 10(5), as an impurity) was studied in the critical binary mixture of nitroethane (NE) + 3-methylpentane (MP) by refractive index measurements. The measurements were performed at three different PEO concentrations (C = 0.373, 0.759, and 1.509 mg/cc) in the near critical composition of NEMP. We observed that the coexisting phase region shifts down with increasing PEO concentration and the critical temperature (T(c)) decreases linearly with C. At temperatures T close enough to T(c), the critical exponent beta [defined by the relation (n1-n2) proportional (T(c)-T)beta, with n1 and n2 being the refractive indices of the coexisting phases] was found to decrease from 0.456 to 0.372 when the PEO concentration changes from 0.373 to 1.509 mg/cc. These values are higher than that of 0.345+/-0.015 of pure NEMP, which is compatible with the three-dimensional Ising value beta = 0.325. It appears that the shape of the PEO in NEMP coexistence curves is similar from that of pure NE + MP.

The coexistence curve of the nitroethane–isooctane mixture is reported. Since the mixture is composed of liquids of nearly perfectly matched refractive indices, special care had to be taken. Two experimental techniques were used: (i) A visual method with 32 samples of different mass function c allowing the exponent β (0.318±0.006) the amplitude B (1.83±0.016 in Δc=Beβ) and the critical composition (isooctane mass fraction 0.5350±6×10−4) to be obtained. (ii) An interferometer method on a single critical sample, giving β=0.31±0.02, the refractive index derivatives (∂n/∂T)p,φ=−(4.99±0.02) ×10−4 and (∂n/∂φ)p,T= (1.38±0.05) ×10−3 and the refractive index difference n1−n2= (0.95±0.04) ×10−3. The interferometer method is influenced by long time‐scale relaxation effects. The value of the exponent β is found to be close to the three‐dimensional Ising value and is nearly insensitive, as is also the quality of the fit, to the choice of the order parameter (volume, mass, or mole fraction). The coexistence curve was found to be entirely symmetrical when the mass fraction was used, and we did not find evidence of deviations from the rectilinear diameter. Nonanalytical corrections were necessary only with the mole fraction parameter when the value β=0.325 was imposed.

Interferometric and diffraction grating measurements of the depolarized light scattering linewidths in the critical region of a nitroethane‐3 methylpentane liquid mixture reveal a relatively weak dependence of the orientational linewidth on ΔT. Plots of the log of the orientational relaxation time vs log ΔT, logτ=−r logΔT+C, yield r=0.031±0.008 while plots of logτ=r′/T+C′ yield r′=1090±292 K. The wide background in the depolarized spectrum exhibits a HWHM of 30 cm−1 which does not change as the critical point is approached. In addition, the HWHM of the completely polarized 875 cm−1 Raman band of nitroethane was found to be 2.1 cm−1 and also to be insensitive to temperature.

Intensity and linewidth measurements of the depolarized Rayleigh line in the critical mixture of nitroethane and isooctane in the temperature range T−Tc=2 m°K−60°K are reported. The linewidth presents no anomaly and behaves like the regular part of the viscosity. The intensity however exhibits a linear anomaly which levels off for T−Tc≳35°K.

We report precise measurements of the density as a function of temperature in the one‐phase region near the consolute point in nitroethane + 3‐methylpentane. We find evidence of the critical anomaly in the thermal expansion, but are not able to determine a unique value for the critical exponent α. We have performed computer experiments to determine under what conditions α could be extracted from thermal expansion data.

Spontaneous Raman spectra have been obtained for three vibrational bands of the binary liquid mixture nitroethane, 3‐methylpentane. Measurements for the one phase region at the critical concentration extend over a broad temperature range down to T−Tc = 0.008 °C. Over this range we have observed no critical anomaly in the vibrational bandwidth. The behavior, both near the critical point and far from it, is not consistent with the predictions of the fast modulation theories of pure dephasing which relate the bandwidth to the viscosity and other liquid properties. It is consistent with a variety of slow modulation limit predictions, but the measurements do not yet provide a definitive test of these theories.

The ultrasonic velocity and attenuation have been measured in the critical binary mixture cyclohexane + nitroethane over the frequency range 3–27 MHz and the temperature range 0.01≤T−Tc≤15 K. The sound velocity varies linearly with T and shows no critical dispersion in this frequency range. The critical attenuation is analyzed in terms of the dynamic scaling theory of Bhattacharjee and Ferrell. In general, the agreement between theory and experiment is good but the data conform to an empirical scaling function that differs in small but systematic ways from the theoretical scaling function. Universality in the critical acoustic behavior is demonstrated by a comparison of the scaled attenuation in three binary liquid systems with that in two pure fluids.

The viscosity of the following binary mixtures was measured near their consolute points: (1) methanol + cyclohexane, (2) isobutyric acid + water, (3) nitroethane + 3-methylpentane, and (4) 2-butoxyethanol + water. It is shown that the multiplicative hypothesis is valid for these mixtures. It is also found that the concentration closest to critical has the largest viscosity enhancement.

The acoustic velocity and attenuation have been measured in a critical mixture of 3‐methylpentane + nitroethane over the frequency range 1–17 MHz and the temperature range 0.004≤T−Tc≤13.5 K. No critical dispersion was observed in the velocity, which varied linearly with T. A substantial critical attenuation was well characterized as a function of the reduced frequency ω*≡ω/ωD over the range 10−1≤ω*≤106. The experimental data in this system are extensive enough to permit quantitative tests of the predictions of dynamic scaling theory, dynamic renormalization‐group theory, and several versions of mode‐coupling theory. Universality in the scaling function for the critical attenuation is demonstrated by comparison with comparable experimental results in two pure fluids.

In a study of the mixture, ethylene glycol + water + lauryl alcohol + nitromethane + nitroethane we have observed a region of four coexisting liquid phases between 37 and 42 °C. Analysis of the compositions of the coexisting phases provides fairly convincing evidence that they belong to a ’’shield’’ region noted previously in theoretical studies of a three‐component model and a van der Waals model of binary mixtures. Such a region could be the starting point in a search for the multicritical point D2. On the other hand its presence is good evidence for the absence in this mixture of the fluid analog of the three‐state Potts model multicritical point C2. This is in agreement with studies in systems with symmetry‐breaking phase transitions and lends support to the hypothesis that C2 does not occur in three‐dimensional systems.

Experimental data are reported for the capillary rise of the interface between the two liquid phases of 3‐methylpentane–nitroethane as a function of temperature. The data are interpreted in terms of a power law currently proposed for the behavior of the interfacial tension near the critical mixing point. The results seem to indicate that for 3‐methylpentane–nitroethane the region of asymptotic behavior is limited to rather small values of ΔT* = (Tc − T) / Tc. For ΔT* ≥ 10−2 Sugden's parameter a2 can be represented by a power law a2 = A2ΔT*φ with an exponent φ = 1.00 ± 0.01. A comparison is made with the behavior of the surface tension of simple one‐component liquids near the gas–liquid critical point.

Shear viscosity coefficients for a mixture of 3‐methylpentane—nitroethane of critical composition were determined over the temperature range 6×10−6≤ e ≤ 2×10−2 by an improved capillary viscometer. The data were analyzed by alternate procedures both of which give strong support to the view that the viscosity singularity is indeed very weak over a wide temperature range.

A theory of the effect of hindered internal rotation on β‐proton coupling constants in free radicals is proposed and discussed. The results of both classical and quantum‐mechanical treatments are applied to recent ESR data on the anion radicals of several nitroalkanes. It is shown that a twofold barrier to internal rotation of magnitude 1.4 kcal/mole can account for the observed variation of proton coupling constants between the nitroethane and 2‐nitropropane anion radicals. The temperature dependence of the coupling constants is predicted. In the equation aβH = (B0+B2 cos2θ)ρπ, it is shown that the term B0 may be attributed to residual torsional motion of β protons in the crystal lattice.

The viscosities of nitroethane‐3‐methylpentane mixtures were measured in an Ostwald viscometer over the entire composition range, and over a temperature range of ΔT(= T ‐ Tc) from 11.673 °C to 0.003 °C. The experimental data of this work show quantitatively that the best fit of the viscosity data is to the equation η = (A/φ) (e−φ − 1) + Be + C, where A/φ = 0.478 ± 0.04, B = − (1.09 ± 0.05), C = 0.335 ± 0.01, and φ = 0.03 ± 0.01. The value of φ is within experimental error positive and not zero. It clearly indicates that at a temperature very close to the critical temperature the anomalous viscosity shows a very weak power law divergence and is not a cusp nor a logarithmic divergence. The excess shear viscosity is approximately related to the composition by a Gaussian distribution in composition centered about the critical composition, X2c: Δη = f(T) exp {− (1/2)[10(X2 − X2c)]2}.

The coexistence curve for the liquid mixture 3‐methylpentane–nitroethane has been obtained using a visual and a float technique. A detailed analysis of the data shows that the composition differences of the coexisting liquid phases are proportional to (tc — rpar;β, where β = 0.340 with a standard deviation of 0.010. As a result of this analysis and an analysis of the earlier work of Rice and Zimm it is shown that the value of β for binary liquids is not significantly different from the value for gas–liquid systems.

From measurements of the rate of neutralisation of a pseudo‐acid, nitroethane, in heavy water, a comparison is made of the relative rates of ionisation of protium and deuterium atoms, the ratio being approximately 10 : 1. It is shown that these relative rates are of great importance in the study of catalysis by acids and bases in heavy water and some conclusions may be drawn with regard to the mechanism of the inversion of sucrose and of the mutarotation of glucose. These results also have a bearing on the question of deuterium‐protium exchange in compounds when dissolved in water.

The infra‐red spectra from 2 to 22μ of nitromethane, nitroethane, 1‐nitropropane and 2‐nitropropane have been obtained for both vapor and liquid phases. The Raman shifts have been measured for the liquids, and for nitromethane the polarizations of the bands have been determined.A satisfactory interpretation of the spectra has been obtained for nitromethane on the basis of assigned fundamental frequencies that agree with those proposed previously by Wells and Wilson, except for the B1 methyl rocking mode. The fundamental frequencies have not been determined for the other compounds, but the positions of the nitro group absorptions have been determined empirically.

The shear viscosities of a critical mixture of nitroethane‐3‐methylpentane were measured near the critical temperature (ΔT values of 0.500 to 0.55°C) over a range of shear rates from 700 to 0.015 sec−1. No shear dependence within experimental error was found at any temperature. The shear viscosities of solutions of polystyrene‐cyclohexane near or at the critical composition were also measured at shear rates from 1500 to 0.1 sec−1 and at a ΔT value of 0.24°C. A constant 10% increase in viscosity at low shear was found for mixtures having concentrations near the critical concentration. Consequently the increase cannot be solely attributed to critical phenomena, but must be related to other polymeric phenomena.

The data of Zalczer and Beysens1 regarding the intensity measurements of depolarized Rayleigh scattering line in a critical mixture of nitroethane and isoctane is analyzed. Similar data of Ref. 2 for pure nitrobenzene is also reexamined. It is concluded that the intensity behavior in the mixture is not associated with a critical anomaly. (AIP)