Gerd M. Rosenblatt

In—Cavity Laser Raman Spectroscopy of Vapors at Elevated Temperatures. As4 and As4O6

The 632.8‐nm radiation inside the cavity of an He–Ne laser is used to excite vibrational Raman spectra of As4 vapor at ∼ 610°C and As4O6 vapor at ∼ 440°C. As4 peaks are observed and assigned as follows: v1(a1), 344 cm−1; v2(e), 210 cm−1; and v3(f2), 255 cm−1. As4O6 vapor peaks are seen at 185, 253, 381, 409, 496, and 555 cm−1. An outside‐cavity room‐temperature spectrum of powdered As4O6 shows bands at 85, 189, 269, 371, 470, 560, and 782 cm−1. At a sample temperature of −178°C, the 85‐cm−1 peak shifts to higher frequency by 4.4 cm−1. The molecular f2 fundamentals of As4O6 vapor are reassigned at 253, 346, 496, and 782 cm−1 based upon the disappearance of the 85‐cm−1 low‐frequency band upon going from solid to vapor, the temperature dependence of the 85‐cm−1 band of the solid, comparison with assignments for P4O6, and comparison of computed absolute entropies of As4O6 vapor with entropies obtained from vapor pressure measurements, as well as literature single‐crystal polarization measurements and infrared...

Rotational Raman scattering from premixed and diffusion flames

Abstract Use of rotational Raman spectroscopy as a flame probe is examined. Results of rotational and vibrational Raman scattering from hydrogen oxygen, methane-air and propane-air flames are presented. Time-averaged temperatures are measured, both below and above the inner cones of the premixed flames, based upon rotational Raman scattering from the major species (N2, O2, H2 and CO2). Corrections for vibrational-rotational interactions and for the effects of rotational transitions from vibratinally excited molecules are included in the temperature calculations. For hydrogen or methane flames, temperatures based upon rotational Raman scattering from N2 or O2 have lower uncertainties (1–4%) than those based upon vibrational Raman scattering (3–9%) because rotational Raman transitions are generally more intense and give rise to many more transitions. Scattering from CO2, H2O, or C3H8 does not seriously interfere with rotational Raman temperature measurements in the flames studied. It is concluded that rotational Raman spectroscopy can be a useful nonperturbing probe of concentrations and temperatures in atmospheric pressure flames. Rotational Raman intensity factors relative to N2, are obtained from room temperature pure rotational Raman spectra to be 2.61 ± 0.13 for O2 and 0.20 ± 0.05 for HCl.

Rate of Vaporization of Arsenic Single Crystals and the Vaporization Coefficient of Arsenic

Rates of vaporization from (111) cleavage faces of arsenic single crystals have been measured over the temperature range 508°–580°K with a recording vacuum microbalance. Expressing the rates as Langmuir vapor pressures (PL), the results are R lnPL(atm) = −(43.99 ± 1.47) / T + (37.98 ± 2.72). At 550°K, PL = 6.60 × 10−10atm. Comparison with literature equilibrium data yields a vaporization coefficient, αυ = PL / PE = 4.6 × 10−5 at 550°K, which increases with temperature, αυ = exp (−10921 / RT). The results are consistent with a vaporization mechanism in which the slow step involves formation of As4 molecules and occurs prior to surface diffusion and desorption. Ancillary measurements on vaporization of wrapped arsenic crystals, powdered arsenic, and Knudsen‐effusion experiments are presented. These data and previous vaporization studies on powdered arsenic are correlated using the concept of effective vaporizing areas. Some implications of the results for the equilibrium vapor pressure of arsenic, the inter...

Evaporation from Solids

Volatilization of solids in the broad sense includes any process which results in conversion of matter from the solid state to the vapor phase. Volatilization may occur in two principal ways. Solid may be converted into vapor by (1) evaporation, in which case the gaseous molecules formed consist entirely of atoms supplied by the solid, or (2) a chemical reaction between the solid and another species to form gaseous products. In the latter case the other species may be a gas, another solid, or a liquid. The additional species may be present inadvertently as part of the environmental gas or of the container material, or may be introduced purposely. Volatilization reactions of this second type are governed by considerations described in other chapters of this treatise (cf. Chapters 4, 5, 8, and 9 of Volume 4). However, although more complex, the reactions of solids with other phases, particularly with gases, to form volatile products are related to, and in some respects similar. to, direct evaporation of gases from solids. Gas-surface volatilization reactions are complicated by the need for interaction, adsorption, and reaction of the incoming gas with the solid, as described in Chapter 5 of Volume 6A and Chapter 8 of Volume 4. However, following, and perhaps during, formation of the product molecules the molecular processes are similar to those occurring during evaporation, as described in this chapter.

Vapor pressure and thermodynamics of octahedral arsenic trioxide (arsenolite)

Abstract Knudsen effusion experiments using a recording vacuum microbalance have been performed on powdered arsenic trioxide (arsenolite) over the temperature range 367 to 429 K. The vapor pressure of arsenolite over this range is (R cal th K −1 mol −1 ) ln( p atm) = − (27759±574) k t + (45.32±1.46). Third-law thermodynamic functions have been approximated for solid arsenolite above 298.15 K. Third-law thermodynamic functions for As4O6(g) have been computed using selected vibrational frequencies based upon available spectroscopic measurements on As4O6(g), and on arsenolite powder and single crystals. A third-law enthalpy of sublimation, ΔHo(298.15 K) = (28.13 ± 0.20) kcalth mol−1, is obtained. The second-law result is ΔHo(298.15 K) = (28.31 ± 0.56) kcalth mol−1. These results are consistent with data of other authors. The agreement between second-law and third-law enthalpies supports the vibrational assignment used to compute the third-law functions and entropy of As4O6(g), So(298.15 K) = (97.81 ± 2.5) calth K−1 mol−1.

Relative raman line intensities for H2 and for D2. Correction factors for molecular non-rigidity

Abstract Ab initio calculations are presented for H 2 and D 2 relative Raman intensities originating from common rotational levels for both vibrational-rotational and pure rotational transitions. Factors f ( J ) required to correct measured intensities for molecular non-rigidity (e.g. in temperature measurements) are tabulated. The calculations are compared with literature perturbation-theory equations (significant differences at large J in vibration-rotation) and with experiment.

Vaporization Kinetics and Thermodynamics of Antimony and the Vaporization Coefficient of Antimony Single Crystals

The vaporization rate of Sb4 from Sb (111) single‐crystal cleavage faces has been measured over the temperature range 606–697°K using a recording vacuum microbalance. The results, expressed as Langmuir vapor pressures PL, yield R lnPL(atm) = −[(49 740 ± 2200)) / T] + (35.67 ± 3.4). At 650°K PL = 1.2 × 10−9atm. Comparison with equilibrium vapor pressures PE yields a vaporization coefficient αυ = PL / PE = 0.17 ± 0.06 at 650°K which increases with temperature αυ = exp(−2310 / RT). The data are corrected for evaporated molecules which return to the sample. Vaporization rates of antimony powder and Kundsen effusion experiments in the same apparatus confirm the value of αυ. The apparent vaporization coefficient from the powder, 0.54, correlates well with the single‐crystal results. Kundsen‐effusion experiments at 683–819°K using a 0.4‐mm‐diam‐orifice aluminum cell give R lnPE(atm) = − 223[(47600 ± 1330) / T] + (35.65 ± 1.79) and a third‐law enthalpy of sublimation ΔH°298 = 49.67 ± 0.32 kcal/mole in good agreem...

Flame temperatures from Raman scattering

Abstract Pure rotational, as well as vibrational Raman scattering has been observed from stable diatomic molecules in high-temperature flames. Accurate (rotational) flame temperatures may be determined from the rotational line intensities. For a hydrogen diffusion flame in air T rot (N 2 ) = 1880 ± 21K, T rot (H 2 ) = 1890 ± 80 K, T vib (N 2 ) = 1995 ± 130 K, and T vib (H 2 ) =1900 ± 150 K.

Infrared spectrum of condensed As4 and thermodynamic functions of As4 gas

Abstract The infrared spectrum of arsenic condensed at −196°C shows a very strong band at 250 cm−1 which is assigned to the ν3 (f2) molecular vibration of As4. By comparison with P4 gas frequency shifts at low temperature and in various environments the value of ν3 for gaseous As4 is estimated to be 260 cm−1. Heat capacities, heat contents, entropies, and free energy functions from 298.15 to 3000°K are presented for As4 (g) based upon this vibration, ν1 (a1) = 339, and ν2 (e) = 203 cm−1 estimated by comparison with P4 (g). The absolute entropy of As4 (g) at 298.15°K is 78.23 ± 0.6 cal/deg mole.

Raman spectroscopy of gaseous GaCl3 and GaI3

Raman spectra of the vapors over GaCl3, GaI3, and Ga–GaI3 mixtures have been obtained at temperatures of 160–960°C, 200–260°C, and 450–650°C, respectively. Three peaks due to GaCl3 are observed: 381 (ν1), 457 (ν3), and 128 cm−1 (ν4). Four peaks are observed for GaI3: 152, 192, 276 (ν3), and 60 cm−1 (ν4). Both GaCl3 and GaI3 are planar (D3h symmetry); the additional polarized peak in GaI3 arises from Fermi resonance involving ν1. The symmetric‐stretch vibrations of all Group IIIa trihalides vary linearly with the inverse of the product of the internuclear distance and the square root of the mass of the halide atom, a trend which implies that all these molecules (BCl3, BBr3, BI3, AlCl3, AlBr3, AlI3, GaCl3, GaBr3, GaI3, InCl3, InBr3, InI3) have D3h symmetry. Thermodynamic functions are presented for GaCl3, GaBr3, and GaI3 based upon the present results.