Temperature-programmed Thermal Desorption Research Articles

Molecular Characterization of the Thermal Degradation of Per- and Polyfluoroalkyl Substances in Aqueous Film-Forming Foams via Temperature-Programmed Thermal Desorption–Pyrolysis–Direct Analysis in Real Time–Mass Spectrometry

Molecular Characterization of the Thermal Degradation of Per- and Polyfluoroalkyl Substances in Aqueous Film-Forming Foams via Temperature-Programmed Thermal Desorption–Pyrolysis–Direct Analysis in Real Time–Mass Spectrometry

Effects of Supports on Pd–Fe Bimetallic Sorbents for Hg0 Removal Activity and Regeneration Performance from Coal-Derived Fuel Gas

Pd–Fe bimetallic sorbents were shown to be a great potential sorbent for Hg0 removal from coal-derived fuel gas. In this work, activated carbon (AC), Al2O3, and Beta molecular sieve were chosen as supports to disperse Pd–Fe bimetallic components. The effects of the supports on Hg0 removal of Pd–Fe bimetallic sorbents were evaluated using a fixed-bed reactor at 200 °C. The regeneration performance of sorbents was also investigated. The results showed that Hg0 removal activity and regeneration performance over Pd–Fe/AC was the best, followed by Pd–Fe/Beta, and Pd–Fe/Al2O3. The Hg0 removal efficiency of Pd–Fe/AC bimetallic sorbents remained above 80% within 400 min after regeneration 4 times. The Pd–Fe bimetallic sorbents were characterized by N2 adsorption–desorption, Fourier transform infrared spectroscopy, X-ray diffraction, CO pulse adsorption, Hg temperature-programmed thermal desorption, and X-ray photoelectron spectroscopy. The analysis results revealed that three sorbents had a similar Hg0 removal me...

An Expanded Gas-grain Model for Interstellar Glycine

The study of the chemical evolution of glycine in the interstellar medium is one of challenging topics in astrochemistry. Here, we present the chemical modeling of glycine in hot cores using the state-of-the-art three-phase chemical model NAUTILUS, which is focused on the latest glycine chemistry. For the formation process of glycine on the grain surface, we obtained consistent results with previous studies that glycine would be formed via the reactions of COOH with CH$_2$NH$_2$. However, we will report three important findings regarding the chemical evolution and the detectability of interstellar glycine. First, with the experimentally obtained binding energy from the temperature programmed thermal desorption (TPD) experiment, a large proportion of glycine was destroyed through the grain surface reactions with NH or CH$_3$O radicals before it fully evaporates. As a result, the formation process in the gas phase is more important than thermal evaporation from grains. If this is the case, NH$_2$OH and CH$_3$COOH rather than CH$_3$NH$_2$ and CH$_2$NH would be the essential precursors to the gas phase glycine. Secondly, since the gas phase glycine will be quickly destroyed by positive ions or radicals, early evolutionary phase of the hot cores would be the preferable target for the future glycine surveys. Thirdly, we suggest the possibility that the suprathermal hydrogen atoms can strongly accelerate the formation of COOH radicals from CO$_2$, resulting in the dramatic increase of formation rate of glycine on grains. The efficiency of this process should be investigated in detail by theoretical and experimental studies in the future.

Preconcentration and partial separation of nitroaromatic vapors using a methyltrimethoxysilane-based sol-gel

Typical trace vapor analysis involves sorbent trapping, followed by desorption and chromatographic separation. This communication describes a method for streamlining this process by combining sorbent sampling/preconcentration with partial separation achieved through temperature-programmed thermal desorption. A novel sorbent trap was formulated in which tubular glass liners for a programmable-temperature gas chromatograph inlet were coated with a sol-gel based polymer stationary phase synthesized from methyltrimethoxysilane precursor and installed into the inlet, which was directly connected to a mass-selective detector by a fused silica capillary transfer line. This method is shown to achieve partial separation of two nitroaromatic vapors in a total 3–5min analysis time, which represents a tenfold improvement in speed in terms of the overall cycle time compared to an analogous conventional vapor analysis method. Both analytes proved to have a high dynamic range and loading capacity, with nitrobenzene achieving both high and low sampling extremes (0.32ng–4μg sampling concentration) with only a slight compromise in peak broadening. The multivariate curve resolution by alternating least squares algorithm (MCR-ALS) was shown to successfully resolve the overlapped elution profiles of the two nitroaromatic test vapors examined in this study.

Phase partitioning and volatility of secondary organic aerosol components formed from α-pinene ozonolysis and OH oxidation: the importance of accretion products and other low volatility compounds

Abstract. We measured a large suite of gas- and particle-phase multi-functional organic compounds with a Filter Inlet for Gases and AEROsols (FIGAERO) coupled to a high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS) developed at the University of Washington. The instrument was deployed on environmental simulation chambers to study monoterpene oxidation as a secondary organic aerosol (SOA) source. We focus here on results from experiments utilizing an ionization method most selective towards acids (acetate negative ion proton transfer), but our conclusions are based on more general physical and chemical properties of the SOA. Hundreds of compounds were observed in both gas and particle phases, the latter being detected by temperature-programmed thermal desorption of collected particles. Particulate organic compounds detected by the FIGAERO–HR-ToF-CIMS are highly correlated with, and explain at least 25–50 % of, the organic aerosol mass measured by an Aerodyne aerosol mass spectrometer (AMS). Reproducible multi-modal structures in the thermograms for individual compounds of a given elemental composition reveal a significant SOA mass contribution from high molecular weight organics and/or oligomers (i.e., multi-phase accretion reaction products). Approximately 50 % of the HR-ToF-CIMS particle-phase mass is associated with compounds having effective vapor pressures 4 or more orders of magnitude lower than commonly measured monoterpene oxidation products. The relative importance of these accretion-type and other extremely low volatility products appears to vary with photochemical conditions. We present a desorption-temperature-based framework for apportionment of thermogram signals into volatility bins. The volatility-based apportionment greatly improves agreement between measured and modeled gas-particle partitioning for select major and minor components of the SOA, consistent with thermal decomposition during desorption causing the conversion of lower volatility components into the detected higher volatility compounds.

Surfaces of complex intermetallic compounds: insights from density functional calculations.

CONSPECTUS: Complex intermetallic compounds are a class of ordered alloys consisting of quasicrystals and other ordered compounds with large unit cells; many of them are approximant phases to quasicrystals. Quasicrystals are the limiting case where the unit cell becomes infinitely large; approximants are series of periodic structures converging to the quasicrystal. While the unique properties of quasicrystals have inspired many investigations of their surfaces, relatively little attention has been devoted to the surface properties of the approximants. In general, complex intermetallic compounds display rather irregular, often strongly corrugated surfaces, making the determination of their atomic structure a very complex and challenging task. During recent years, scanning tunneling microscopy (STM) has been used to study the surfaces of several complex intermetallic compounds. If atomic resolution can be achieved, STM permits visualization of the local atomistic surface structure. However, the interpretation of the STM images is often ambiguous and sometimes even impossible without a realistic model of the structure of the surface and the distribution of the electronic density above the surface. Here we demonstrate that ab initio density functional theory (DFT) can be used to determine the energetics and the geometric and electronic structures of the stable surfaces of complex intermetallic compounds. Calculations for surfaces with different chemical compositions can be performed in the grand canonical ensemble. Simulated cleavage experiments permit us to determine the formation of the cleavage planes requiring the lowest energy. The investigation of the adsorption of molecular species permits a comparison with temperature-programmed thermal desorption experiments. Calculated surface electronic densities of state can be compared with the results of photoelectron spectroscopy. Simulations of detailed STM images can be directly confronted with the experimental results. Detailed results are presented for two intermetallic compounds that have recently attracted much attention as active and highly selective catalysts for the semihydrogenation of alkynes to alkenes, but the identification of the catalytically active surfaces was found to be very difficult. The crystal structure of B20-type GaPd can be interpreted as the lowest order approximant of icosahedral Al-Pd-Mn quasicrystals. Among the low-index surfaces, the {100} surface shows 2-fold symmetry and the {210} surface pseudo-5-fold symmetry; for both the surface stoichiometry is identical to that of the bulk. Because the structure lacks inversion symmetry, the {111} surfaces have polar character and permit terminations of widely different chemical composition. Results for all three surfaces are presented and compared with the available experiments. The crystal structure of orthorhombic Al13Co4 is built by pentagonal clusters similar to those found in decagonal Al-Co and Al-Ni-Co quasicrystals. A simulated cleavage experiment shows that the constituent clusters remain intact upon cleavage, resulting in the formation of a highly corrugated (100) surface. The calculated STM images are found to be in very good agreement with experiment and permit in addition identification of possible surface modifications by the desorption of individual atoms. Pentagonal motifs on the {210} surface of GaPd and on the (100) surface of Al13Co4 consisting of simple- and transition-metal atoms have been identified as the catalytically active centers for the semihydrogenation of acetylene to ethylene.

A novel method for online analysis of gas and particle composition: description and evaluation of a Filter Inlet for Gases and AEROsols (FIGAERO)

Abstract. We describe a novel inlet that allows measurement of both gas and particle molecular composition when coupled to mass spectrometric, chromatographic, or optical sensors: the Filter Inlet for Gases and AEROsols (FIGAERO). The design goals for the FIGAERO are to allow unperturbed observation of ambient air while simultaneously analyzing gases and collecting particulate matter on a Teflon® (hereafter Teflon) filter via an entirely separate sampling port. The filter is analyzed periodically by the same sensor on hourly or faster timescales using temperature-programmed thermal desorption. We assess the performance of the FIGAERO by coupling it to a high-resolution time-of-flight chemical-ionization mass spectrometer (HRToF-CIMS) in laboratory chamber studies of α-pinene oxidation and field measurements at a boreal forest location. Low instrument backgrounds give detection limits of ppt or lower for compounds in the gas-phase and in the picogram m−3 range for particle phase compounds. The FIGAERO-HRToF-CIMS provides molecular information about both gases and particle composition on the 1 Hz and hourly timescales, respectively for hundreds of compounds. The FIGAERO thermal desorptions are highly reproducible (better than 10%), allowing a calibrated assessment of the effective volatility of desorbing compounds and the role of thermal decomposition during the desorption process. We show that the often multi-modal desorption thermograms arising from secondary organic aerosol (SOA) provide additional insights into molecular composition and/or particle morphology, and exhibit changes with changes in SOA formation or aging pathways.

Interaction of Hydrogen with a Cobalt(0001) Surface

Abstract The interaction of hydrogen and deuterium with the Co(0001) surface has been studied in UHV between 90 and 500 K by means of LEED, temperature-programmed thermal desorption (TPD) and work function change (ΔΦ) measurements. Hydrogen adsorbs spontaneously and dissociatively in two atomic binding states denoted as β 1 and β 2 with a high initial sticking probability. The adsorption energies E(β 1) and E(β 2) are 80 and 100 kJ/mol, respectively, if a first-order desorption kinetics is assumed (a second-order kinetic analysis yields unreasonably low values for both the desorption energies and frequency factors). At sufficiently low temperatures, the adsorbed H atoms form a faint (2 × 2) LEED superstructure, which is best developed after an exposure of ∼20 L. From the temperature dependence of the fractional-order beam intensity at different exposures we determine the critical temperature of the (2 × 2) phase as ∼ 243 ( ± 10) K. Similar to the H-on-Ni(111) system the existence range of the (2 × 2) phase in the temperature–coverage plane is asymmetric; i.e., below the critical coverage Θ crit the respective long-range order has a higher range of stability than above Θ crit. By analogy with H/Ni(111), we assume a similar honeycomb H structure also for the H-on-Co(0001) system and suggest the critical coverage Θ crit to be 0.5, i.e., half a monolayer of H atoms. The H-induced work function change is surprisingly small; it decreases, forms a shallow minimum of −18 meV after ∼20 L exposure around the optimum coverage of the (2 × 2) phase and reaches a saturation value of −10 meV. Our data are discussed and compared with previous work on H/Co(0001) and other close-packed transition metal surfaces, especially with the H-on-Ni(111) system.

Interaction of copper with the rhenium surface

We have studied the adsorption of copper on the clean Re surface between 300 and 900 K by means of low- and medium-energy electron diffraction (LEED and MEED) and temperature-programmed thermal desorption (TPD). The persistence of a (1 × 1) LEED pattern during Cu deposition suggests the formation of pseudomorphic Cu islands. Accordingly, the intensity–voltage behaviour of the (1 × 1) LEED beams can be quantitatively superimposed by the coverage-weighed fractions of the I(V)-curves of uncovered Re areas and of Cu-covered (1 × 1) islands. At a coverage of 1.625 × 1019 Cu atoms m−2 dynamical LEED I(V) calculations suggest a full hcp-oriented Cu bilayer (BL). Within this first BL, Cu wets the Re surface completely, while all following layers exhibit remnant roughness due to small Cu nuclei, as confirmed by in situ grazing-incidence MEED experiments. The completion of the first BL coincides with the saturation of a single β TPD state at 1180 K, whilst higher coverages produce an additional zero-order α state, which peaks at 1080 K at 2.6 BL. The energy of desorption rises from 320 kJ mol−1 at small coverages to ∼360 kJ mol−1 for a bilayer Cu film, pointing to attractive lateral Cu–Cu interactions. An analysis of the leading edge of the multilayer α state yields a desorption energy of ∼305 kJ mol−1, somewhat lower than the sublimation enthalpy of bulk Cu. Our data are discussed and compared with previous results on related systems.

Interactions between glycine and amorphous solid water nanoscale films

The interactions of glycine (Gly) with amorphous solid water (ASW) nanolayers (≤100ML), vapor-deposited on single crystalline AlOx surfaces at 100K, have been investigated by near-edge X-ray absorption fine structure spectroscopy (NEXAFS) at the oxygen K-edge, temperature-programmed thermal desorption (TPD), X-ray photoelectron spectroscopy (XPS), and temperature-dependent work function measurements. Gly-on-ASW, ASW-on-Gly, and Gly on top of ASW-on-Gly ultrathin films have been fabricated. In contrast to the uniform ASW films grown directly on the hydrophilic AlOx, water molecules adsorb on the hydrophobic Gly films in the form of 3D ASW clusters. This leads to significant differences in the NEXAFS and work function data obtained from ASW-on-AlOx and ASW-on-Gly films, respectively. Furthermore, these structural differences influence the chemical state of Gly molecules (neutral vs. zwitterionic) adsorbed on top of ASW films. N1s XPS measurements revealed an increased amount of neutral Gly molecules in the film top-deposited on the ASW-on-Gly structure in comparison to the neutral Gly in the films directly condensed on AlOx or grown on the ASW substrate. H2O TPD spectra demonstrate that the crystallization and desorption processes of ASW are affected in a different way by the Gly layers, top-deposited on to ASW-on-AlOx and ASW-on-Gly films. At the same time, Gly adlayers sink into the ASW film during crystallization/desorption of the latter and land softly on the alumina surface in the form of zwitterionic clusters.

Chemistry of Secondary Organic Aerosol Formation from OH Radical-Initiated Reactions of Linear, Branched, and Cyclic Alkanes in the Presence of NOx

The effects of molecular structure on the products and mechanisms of SOA formation from OH radical-initiated reactions of linear, branched, and cyclic alkanes in the presence of NO x were investigated in a series of environmental chamber experiments. SOA mass spectra were obtained in real time and off line using a thermal desorption particle beam mass spectrometer and used to identify reaction products. Real-time mass spectra were used to classify products according to their temporal behavior, and off-line temperature-programmed thermal desorption analysis of collected SOA was used to separate products by volatility prior to mass spectral analysis and to gain information on compound vapor pressures. A reaction mechanism that includes gas- and particle-phase reactions was developed that explains the formation of SOA products and is consistent with the various lines of mass spectral information. Results indicate that the SOA products formed from the reactions of linear, branched, and cyclic alkanes are simi...

Molecular adsorption and growth of naphthalene films on Ag(1 0 0)

The adsorption of naphthalene, vacuum deposited on a Ag(1 0 0) surface, was comprehensively investigated by means of low-energy electron diffraction (LEED), temperature-programmed thermal desorption (TPD) spectroscopy, X-ray photoelectron spectroscopy (XPS), and polarization-dependent near-edge X-ray absorption fine structure (NEXAFS) spectroscopy in the mono- and multilayer regime. A growth of long-range ordered monolayer at 140 K is observed with LEED. The polarization-dependent C 1s NEXAFS shows that the naphthalene molecules in the monolayer lie almost parallel to the Ag(1 0 0) surface. With increasing film thickness, the molecular orientation turns to upright position. Furthermore, NEXAFS measurements show that in the multilayer regime the molecular orientation depends on the substrate temperature during deposition.

Interaction of glycine with ice nanolayers

The interaction of glycine with ultrathin amorphous and polycrystalline ice films, deposited on crystalline alumina surfaces at 110 and 150 K, respectively, has been studied by temperature programmed thermal desorption (TPD). The TPD spectra demonstrate that the desorption of water is significantly influenced by the presence of glycine molecules, whereas the TPD of glycine is unaffected. It is proposed that the glycine molecules restrict the crystallisation of amorphous to crystalline ice and that the glycine overlayers stabilise the ice surface by attractive interactions.

Dissociation of Carbon Monoxide on the Rhenium(10-10) Surface

We have studied the interaction of carbon monoxide with a Re(10-10) surface between 150 and 800 K by means of low-energy electron diffraction (LEED), temperature-programmed thermal desorption, and ...

An integrated system for surface science measurements of adsorbed species on ice surface under UV laser irradiation: application to water vapour deposition, reaction and desorption processes

A Knudsen-cell type reactor equipped with a grazing angle reflection absorption infrared (RAIR) spectrometer and a temperature-programmed thermal desorption (TPD) system has been devised for investigating adsorption, desorption and reaction processes on ice surface, sometimes under UV light irradiation. In the Knudsen-cell chamber is settled a temperature-controlled Au surface on which a desired amount of water vapour, and then a desired amount of target gases can be deposited. The surface can be covered or opened with a sliding cover from outside. The pressure in the Knudsen-cell chamber before and during the deposition is monitored, from which the uptake coefficient is estimated. Adsorbed species on ice surface and ice film are monitored during adsorption and desorption by grazing angle RAIR spectroscopy. The reactor was used for investigating the adsorption and desorption processes of water. The reaction under 193 nm UV laser irradiation was also studied. The uptake coefficient of water vapour on the ice film at 120 K was found to be 0.45 ± 0.2, weakly depending on the pressure of water vapour above the surface. The RAIR spectral shape of the ice film changed during the adsorption and desorption processes, slightly differently for the two processes. The UV laser irradiation made a small change in the RAIR spectra of the OH stretching region, although the activation energy for the desorption of the ice film was not different before and after substantial UV irradiation. The principal part of the deposited ice film was thus kept un-reacted during the UV irradiation.

Evolution of water vapor from indium-tin-oxide transparent conducting films fabricated by dip coating process

Tin-doped indium oxide In2O3 (indium-tin-oxide) transparent conducting films were fabricated on silicon substrates by a dip coating process. The thermal analysis of the ITO films was executed by temperature-programmed desorption (TPD) or thermal desorption spectroscopy (TDS) in high vacuum. Gas evolution from the ITO film mainly consisted of water vapor. The total amount of evolved water vapor increased on increasing the film thickness from approx. 25 to 250 nm and decreased by increasing the preparation temperature from 365 to 600°C and by annealing at the same temperature for extra 10 h. The evolution occurred via two steps; the peak temperatures for 250 nm thick films were approx. 100-120 and 205-215°C. The 25 nm thick films evolved water vapor at much higher temperatures; a shoulder at approx. 150-165°C and a peak at approx. 242°C were observed. The evolution temperatures increased by increasing the preparation and the annealing temperatures except in case of the second peak of the 25 nm thick films. The evolution of water vapor at high temperature was tentatively attributed to thermal decomposition of indium hydroxide, In(OH)3, formed on the surface of the nm-sized ITO particles.

Chemical reactivity of the V–Pd(1 1 1) subsurface alloy: adsorption of CO

The reactivity of a V–Pd(111)(√3×√3)R30° subsurface alloy has been investigated, using the adsorption of CO as a test case, by photoelectron spectroscopy with synchrotron radiation of the valence and core states and by kinetic analysis of temperature-programmed thermal desorption spectra. The overall conclusion from this study is that the chemical reactivity towards CO is lowered on the subsurface alloy surface as compared to unmodified Pd(111). The photoemission data indicate that the room-temperature CO saturation coverage is reduced from 0.5 monolayer (ML) on the clean Pd(111) surface to ∼0.28–0.30 ML on the alloy surface, in excellent agreement with the thermal desorption results. This is explained in terms of a reduced CO adsorption energy, as revealed by the kinetic analysis of the thermal desorption spectra. The balance between threefold hollow and bridge CO adsorption sites at saturation coverage is changed in favour of the preferential occupation of hollow sites on the alloy surface. The observed modifications of the electronic structure of valence states upon alloying and on CO adsorption are well reproduced by a recent ab initio DFT study of CO on V–Pd alloys by Hirschl and Hafner [Surf. Sci. 498 (2002) 37].

Simple systemfor part-per-billion-level volatile organic compound analysisin groundwater and urban air

A simple device is described, capable of measuringreliably and reproducibly low levels (0.1 ppbv with a totalanalysis time of approximately 40 min) of volatile organiccompounds (VOCs) in urban air andin the headspace of groundwater. The VOCs were pre-concentratedonto a small bed of Tenax TA®, and subsequently releasedby temperature-programmed thermal desorption (TPD). TPD profileswere recorded by a solid-state sensor array. The success of themethod was based on a well defined TPD peak shape if theabsorbent bed was sufficiently thin, linearity and additivity ofappropriately transformed sensor signals, the use of a verystable sensor array utilizing chromium-titanium oxide as thesensor material and devices with different electrode gaps andthe use of dry air as the carrier gas. Successful analysis ofgroundwater headspace was achieved by diluting the samplestream 1:4 with dry air (which prevented saturation of theadsorbent surface by water) and by introducing a dry air purgeof the bed at room temperature before desorption (which removedexcess water from the bed and hence stabilized the sensorbaseline before the desorption). Principal componentsanalysis and spectral decomposition (SD) methods were usedsuccessfully for identification of VOCs and quantification insimple mixtures. The SD method expressed the measured desorption trace on the elements of the sensor array as the sumof a small number of sensor array spectra. The individualdesorption traces for each characteristic sensor spectrum thusderived could be further resolved by a peak fitting procedurebecause the TPD trace had a well defined form, in which bothpeak temperature and peak width in TPD correlated with the boiling temperature of the VOCs, and peak width varied accordingto functional type: phenols>aliphatics>alkyl-substituted benzenes.

The adsorption of xenon on a ruthenium(1 0 [formula omitted] 0) surface

The interaction of xenon with a ruthenium(1 0 1 ̄ 0) surface was investigated between 29 and 300 K by means of low-energy electron diffraction (LEED), temperature-programmed thermal desorption (TPD), and work function ( ΔΦ) measurements. TPD reveals a single desorption state at 135 K (coverage Θ=0.01 ML) which shifts to lower temperatures as Θ increases and appears at 112 K for Θ=0.78 ML. The initial desorption energy is 28.5 kJ/mol and decreases with Θ; at Θ=0.78 ML it is merely 20 kJ/mol. Beyond this coverage there appears another, relatively sharp, desorption state at 88 K which is due to a phase transformation within the Xe monolayer. For coverages 1< Θ⩽1.35 ML, Xe desorbs via zero-order kinetics, with a desorption energy of 17.5 kJ/mol. LEED reveals several phases with long-range order. At Θ=0.5 ML, a (3×1) pattern, and at Θ=0.78 ML, a (2×5) structure is observed. For 0.78< Θ<1 ML a quasihexagonally, uniaxial commensurate (UC) structure is formed which consists of chains of Xe atoms with a mutual Xe–Xe distance of 4.2 (±0.1) Å in [1 2 ̄ 1 0] direction. Work function measurements show a strong decrease even at small Xe coverages; at Θ=0.78 ML, pronounced depolarization effects become effective, leading to a minimum of the ΔΦ( Θ)-curve near the monolayer coverage. At Θ=1 ML, a ΔΦ of −1.29 eV is reached. The data are discussed and the results are compared with other noble gas adsorption systems in view of the peculiar features, namely the clear evidence of repulsive Xe–Xe interactions, the extraordinary large work function change, and the formation of a multilayer phase with square symmetry.

A method for measuring vapor pressures of low-volatility organic aerosol compounds using a thermal desorption particle beam mass spectrometer.

A temperature-programmed thermal desorption method for measuring vapor pressures of low-volatility organic aerosol compounds has been developed. The technique employs a thermal desorption particle beam mass spectrometer we have recently developed for real-time composition analysis of organic aerosols. Particles are size selected using a differential mobility analyzer, sampled into a high-vacuum chamber as an aerodynamically focused beam, collected by impaction on a cryogenically cooled surface, slowly vaporized by resistive heating, and analyzed in a quadrupole mass spectrometer. A simple evaporation model developed from the kinetic theory of gases is used to calculate compound vapor pressures over the temperature range of evaporation. The data are fit to a Clausius-Clapeyron equation to obtain a relationship between vapor pressure and temperature and to determine the heat of vaporization. The technique has been evaluated using C13-C18 monocarboxylic and C6-C8 dicarboxylic acids, which have vapor pressures at 25 degrees C of approximately 10(-4) - 10(-6) Pa, but less volatile compounds can also be analyzed. The method is relatively simple and rapid and yields vapor pressures and heats of vaporization that are in good agreement with literature values. The technique will be used to generate a new database of vapor pressures for low-volatility atmospheric organic compounds.