Gas Molecular Mass Research Articles

The Giant Low Surface Brightness Galaxy Malin 1: New Constraints for Its Molecular Gas Mass from GBT/ARGUS Observations

We report on results from GBT/ARGUS 12CO(1-0) observations for the giant low surface brightness galaxy Malin 1, which allow us to determine an upper limit for its CO mass, and hence its molecular gas mass and molecular gas mass surface density . Although we performed very deep observations through 17 hr on-source integration time, reaching a noise level of ∼0.2 mK (T ) with a corresponding extended source CO limit (3σ) of 0.09 K km s−1, 19 times more sensitive than previous works, we do not detect the 12CO(1-0) emission line. However, the observations allow us to estimate an upper limit (3σ) for the CO mass of about 7.4 × 109 M ⊙ for the extended emission, and 1.4 × 108 M ⊙ for the central part of the galaxy. With these figures we conclude that the molecular gas surface density is lower than 0.3 M ⊙ pc−2, and the corresponding molecular to atomic gas mass ratio is lower than 0.13. The evidence suggests quite different physical conditions for the interstellar medium in Malin 1 compared to that of normal, high surface brightness spirals. This, in one way to another, keeps an usual molecular gas tracer as CO hidden from our observations, in spite of the diverse stellar and structural properties of Malin 1 observed by several authors since more than 30 yr.

CO-CAVITY pilot survey: Molecular gas and star formation in void galaxies

Context. Voids are the most under-dense large-scale regions in the Universe. Galaxies inhabiting voids are one of the keys for understanding the intrinsic processes of galaxy evolution, as external factors such as multiple galaxy mergers or a dense self-collapsing environment are negligible. Aims. We present the first molecular gas mass survey of void galaxies. We compare these new data together with data for the atomic gas mass (MH I) and star formation rate (SFR) from the literature to those of galaxies in filaments and walls in order to better understand how molecular gas and star formation are related to the large-scale environment. Methods. We observed at the IRAM 30 m telescope the CO(1−0) and CO(2−1) emission of 20 void galaxies selected from the Void Galaxy Survey, with a stellar mass range from 108.5 to 1010.3 M⊙. We detected 15 objects in at least one CO line. We compared the molecular gas mass (MH2), the star formation efficiency (SFE = SFR/MH2), the atomic gas mass, the molecular-to-atomic gas mass ratio, and the specific star formation rate (sSFR) of the void galaxies with two control samples of galaxies in filaments and walls, selected from xCOLD GASS and EDGE-CALIFA, for different stellar mass bins and taking the star formation activity into account. Results. In general, we do not find any significant differences between void galaxies and the control sample. In particular, we do not find any evidence for a difference in the molecular gas mass or molecular gas mass fraction. For the other parameters (SFE, atomic gas mass, molecular-to-atomic gas mass ratio, and sSFR), we also find similar (within the errors) mean values between void and filament and wall galaxies when the sample is limited to star-forming galaxies. We find no evidence for an enhanced sSFR in void galaxies. Some tentative differences emerge when trends with stellar mass are studied: The SFE of void galaxies might be lower than in filament and wall galaxies for low stellar masses, and there might be a trend of increasing deficiency in the HI content in void galaxies compared to galaxies in filaments and walls for higher stellar masses, accompanied by an increase in the molecular-to-atomic gas mass ratio. However, all trends with stellar mass are based on a low number of galaxies and need to be confirmed for a larger sample. Conclusions. The results for the molecular gas mass for a sample of 20 voids galaxies allowed us to make a statistical comparison to galaxies in filaments and walls for the first time. We do not find any significant differences of the molecular gas properties and the SFE, but we note that a larger sample is necessary to confirm this and be sensitive to subtle trends.

Study on Relative Electrical Strength of SF6 Substitute Gas Based on Density Functional Theory

In order to achieve the goal of “double carbon” as soon as possible, SF₆ substitute gas is more environmentally friendly and applied in electrical equipment. Based on density functional theory (DFT), the ionization energy, polarizability and HOMO-LUMO energy level of the SF₆ substitute gas were calculated. First, some relevant electrical parameters representing the substitute gas were linearly fitted to their experimental values. Secondly, the prediction simulation equation of the relative electric strength of the substitute gas is obtained by multivariate nonlinear fitting, and then the prediction results are screened. Finally, the relationship between the electrical parameters of the surrogate gas molecule and the relationship between the relative molecular mass under the external electric field is further studied. The research results show that the ionization energy, average electron polarizability and HOMO-LUMO energy level of substitute gas molecules have a strong positive correlation with their relative electric strength, and HFOtype substitute gases can be used as SF₆ substitute gases. Under the external electric field, the ionization energy and HOMO-LUMO level of the surrogate gas molecules decrease with the increase of the gas molecular mass, and the average electron polarizability increases with the increase of the gas molecular mass. For the screening of alternative gases, the carbon chain should be selected to be shorter, the relative molecular mass is more significant, and the average molecular weight is higher. The fluoride of the electron polarizability functional group provides a more precise direction for screening SF₆ substitute gases and has a particular guiding significance.

A parameter-free physical model for gas–surface interaction

Phenomenological gas–surface interaction models and various slip models are nowadays used as the boundary condition in the study of rarefied gas flows and microflows at the microscopic and macroscopic levels, respectively. However, most existing models depend on certain accommodation coefficients which are difficult to be determined prior to application. A physical-based gas–surface interaction model developed recently shows great flexibility and promising performance in capturing the complex gas–surface interaction process at the boundary. Particularly, the new model only employs three input parameters with clear physical meanings. In this work, a “bottom-up” approach for determining the input parameters of the model from the microscopic properties of the gas–surface system is explored. Because of the limitation of the estimation model for the local collision accommodation coefficient, this approach is restricted to light gas-heavy solid surface systems. Consequently, the physical-based gas–surface interaction model no longer involves unknown parameters like the accommodation coefficients in the traditional boundary conditions for rarefied gas flows. Benchmarked by molecular dynamics simulations of the non-isothermal gas–surface interaction process, the parameter-free gas–surface interaction model can accurately predict the reflected velocity distribution as well as the accommodation coefficients on the surface with different corrugation, binding strength, and relative stiffness. Its capability of capturing the influences of surface temperature and gas molecular mass on the gas–surface energy exchange is also demonstrated.

CO observations of major merger pairs at z = 0: molecular gas mass and star formation

We present CO observations of 78 spiral galaxies in local merger pairs. These galaxies represent a subsample of a Ks-band-selected sample consisting of 88 close major-merger pairs (HKPAIRs), 44 spiral–spiral (S+S) pairs, and 44 spiral–elliptical (S+E) pairs, with separation <20 h−1 kpc and mass ratio <2.5. For all objects, the star formation rate (SFR) and dust mass were derived from Herschel PACS and SPIRE data, and the atomic gas mass, MHI, from the Green Bank Telescope HI observations. The complete data set allows us to study the relation between gas (atomic and molecular) mass, dust mass, and SFR in merger galaxies. We derive the molecular gas fraction (MH2/M*), molecular-to-atomic gas mass ratio (MH2/MHI), gas-to-dust mass ratio and SFE (= SFR/MH2) and study their dependences on pair type (S+S compared to S+E), stellar mass, and the presence of morphological interaction signs. We find an overall moderate enhancement (∼2×) in both molecular gas fraction (MH2/M*) and molecular-to-atomic gas ratio (MH2/MHI) for star-forming galaxies in major-merger pairs compared to non-interacting comparison samples, whereas no enhancement was found for the SFE nor for the total gas mass fraction ((MHI + MH2)/M*). When divided into S+S and S+E, low mass and high mass, and with and without interaction signs, there is a small difference in SFE, a moderate difference in MH2/M*, and a strong difference in MH2/MHI between subsamples. For the molecular-to-atomic gas ratio MH2/MHI, the difference between S+S and S+E subsamples is 0.55 ± 0.18 dex and between pairs with and without interaction sign 0.65 ± 0.16 dex. Together, our results suggest that (1) star formation enhancement in close major-merger pairs occurs mainly in S+S pairs after the first close encounter (indicated by interaction signs) because the HI gas is compressed into star-forming molecular gas by the tidal torque; and (2) this effect is much weakened in the S+E pairs.

Planck’s Dusty GEMS

The bright 3P1–3P0 ([CI] 1–0) and 3P2–3P1 ([CI] 2–1) lines of atomic carbon are becoming more and more widely employed as tracers of the cold neutral gas in high-redshift galaxies. Here we present observations of these lines in the 11 galaxies of the set of Planck’s Dusty GEMS, the brightest gravitationally lensed galaxies on the extragalactic submillimeter sky probed by the Planck satellite. We have [CI] 1–0 and [CI] 2–1 measurements for seven and eight of these galaxies, respectively, including four galaxies where both lines have been measured. We use our observations to constrain the gas excitation mechanism, excitation temperatures, optical depths, atomic carbon and molecular gas masses, and carbon abundances. Ratios of LCI/LFIR are similar to those found in the local universe, and suggest that the total cooling budget through atomic carbon has not significantly changed in the last 12 Gyr. Both lines are optically thin and trace 1 − 6 × 107 M⊙ of atomic carbon. Carbon abundances, XCI, are between 2.5 and 4 × 10−5, for an ultra-luminous infrared galaxy (ULIRG) CO-to-H2 conversion factor of αCO = 0.8 M⊙ / [K km s−1 pc2]. Ratios of molecular gas masses derived from [CI] 1–0 and CO agree within the measurement uncertainties for five galaxies, and agree to better than a factor of two for another two with [CI] 1–0 measurements, after carefully taking CO excitation into account. This does not support the idea that intense, high-redshift starburst galaxies host large quantities of “CO-dark” gas. These results support the common assumptions underlying most molecular gas mass estimates made for massive, dusty, high-redshift starburst galaxies, although the good agreement between the masses obtained with both tracers cannot be taken as independent confirmation of either αCO or XCI.

Impact of Pore Geometry and Water Saturation on Gas Effective Diffusion Coefficient in Soil

Gas flow in soil plays a crucial role in terrestrial ecosystems, and numerical simulation of their movement needs to know their effective diffusion coefficients. How pore structure influences the effective diffusion coefficient has been studied intensively for dry porous media, but much remains unknown for unsaturated soils. Here, we employed the X-ray tomography technique at the pore scale to directly obtain the soil structures, the geometry of their pores and the water distribution under different water saturation levels were calculated using a morphological model. The results show that pore structures including porosity, interface area of gas–solid–water and pore diameter are closely related to water saturation. The increase of mean pore diameter with gas saturation can be fitted into a power law. We also investigated the impact of pore geometry and water saturation on the effective diffusion coefficients, which is independent of the molecular mass of gas after normalization. As the normalized effective Knudsen diffusion coefficient increases with average pore diameter following a power law, with the scaling factor related to pore geometry and the exponent is a constant, we explained and proved that the Knudsen diffusion coefficient increases with gas saturation, also following a power law.

Transport Resistances in Fuel-Cell Catalyst Layers

Catalyst layers (CLs) in polymer-electrolyte fuel cells have garnered the attention of researchers due to their association with high local mass-transport resistance at low catalyst loadings [1, 2]. Nevertheless, the genesis and nature of CL resistance(s) is still under debate. CLs are only a few micrometers thick with complex geometry and heterogeneous phases making in-situ examination of CL transport processes extremely difficult. In this study, we probe the nature of CL resistances experimentally and theoretically. Using a hydrogen-pump limiting-current modality, we deconvolute the various gas-transport-related resistances without the impact of those associated with the oxygen-reduction reaction (e.g., water production) [3]. An analytical model to quantify the experimental measurements is developed to analyze the data and to elucidate limiting regimes. Our new results are in agreement with literature limiting-current measurements. Similar to previously reported studies [4], the model demonstrates that the transport of the reactant to the surface through the ionomer film tends to be the dominant resistance in CLs with a linear dependence on the inverse of Pt loading (i.e., roughness factor) [5]. Further, we study the dependence of this resistance on operational parameters including pressure, RH, temperature, gas molecular mass, and ionomer type. The garnered information exposes the controlling resistances, especially in comparison to ex-situ ionomer thin-film properties. Our efforts can be utilized to understand and develop mitigation strategies for local CL resistances. Acknowledgements We would like to thank helpful discussions and data provided by KC Neyerlin at NREL. This work was funded under the Fuel Cell Performance and Durability Consortium (FC PAD) funded by the Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, of the U. S. Department of Energy under contract number DE-AC02-05CH11231.

Molecular-dynamics study on characteristics of energy and tangential momentum accommodation coefficients.

Gas-surface interaction is studied by the molecular dynamics method to investigate qualitatively characteristics of accommodation coefficients. A large number of trajectories of gas molecules colliding to and scattering from a surface are statistically analyzed to calculate the energy (thermal) accommodation coefficient (EAC) and the tangential momentum accommodation coefficient (TMAC). Considering experimental measurements of the accommodation coefficients, the incident velocities are stochastically sampled to represent a bulk condition. The accommodation coefficients for noble gases show qualitative coincidence with experimental values. To investigate characteristics of these accommodation coefficients in detail, the gas-surface interaction is parametrically studied by varying the molecular mass of gas, the gas-surface interaction strength, and the molecular size of gas, one by one. EAC increases with increasing every parameter, while TMAC increases with increasing the interaction strength, but decreases with increasing the molecular mass and the molecular size. Thus, contradictory results in experimentally measured TMAC for noble gases could result from the difference between the surface conditions employed in the measurements in the balance among the effective parameters of molecular mass, interaction strength, and molecular size, due to surface roughness and/or adsorbed molecules. The accommodation coefficients for a thermo-fluid dynamics field with a temperature difference between gas and surface and a bulk flow at the same time are also investigated.

Time-dependent methodology for non-stationary mass flow rate measurements in a long micro-tube

This paper reports the experimental and numerical analysis of time-dependent rarefied gas flows through a long metallic micro-tube. The experimental methodology was conceived on the basis of the constant volume technique and adapted to measure the evolution with time of a transient mass flow rate through a micro-tube. Furthermore, the characteristic time of each experiment, extracted from the pressure measurements in each reservoir, offered a clear indication on the dynamics of the transient flow as a function of the gas molecular mass and its rarefaction level. The measured pressure evolution with time at the inlet and outlet of the micro-tube was compared to numerical results obtained with the BGK linearized kinetic equation model. Finally, we present an original methodology to extract stationary mass flow rates by using the tube conductance, which can be associated with the characteristic time of the experiment, measured for different mean pressures between two tanks. The results were obtained in a wide range of rarefaction conditions for nitrogen ( $$N_2$$ ). A brief comparison is offered with respect to R134a (CH2FCF3), too, a heavy polyatomic gas which is typically used in the refrigeration industry.

Time-resolved laser-induced incandescence characterization of metal nanoparticles

This paper presents a comparative analysis of time-resolved laser-induced incandescence measurements of iron, silver, and molybdenum aerosols. Both the variation of peak temperature with fluence and the temperature decay curves strongly depend on the melting point and latent heat of vaporization of the nanoparticles. Recovered nanoparticle sizes are consistent with ex situ analysis, while thermal accommodation coefficients follow expected trends with gas molecular mass and structure. Nevertheless, there remain several unanswered questions and unexplained behaviors: the radiative properties of laser-energized iron nanoparticles do not match those of bulk molten iron; the absorption cross sections of molten iron and silver at the excitation laser wavelength exceed theoretical predictions; and there is an unexplained feature in the temperature decay of laser-energized molybdenum nanoparticles immediately following the laser pulse.

THE GLOBAL STAR FORMATION LAWS OF GALAXIES FROM A RADIO CONTINUUM PERSPECTIVE

We study the global SF law - the relation between gas and SFRs in a sample of 181 local galaxies with L_IR spanning almost five orders of magnitude, which includes 115 normal galaxies and 66 (U)LIRGs. We derive their atomic, molecular gas and dense molecular gas masses using newly available HI, CO and HCN data from the literature, and SFRs are determined both from total IR and 1.4 GHz radio continuum (RC) luminosities. In order to derive the disk-averaged surface densities of gas and SFRs, we have used high-resolution RC observations to measure the radio sizes for all galaxies. We find that dense molecular gas (as traced by HCN) has the tightest correlation with that of SFRs, and is linear in (N=1.01 +/- 0.02) across the full galaxy sample. The correlation between densities of molecular gas (traced by CO) and SFRs is sensitive to the adopted value of the alpha_CO used to infer molecular gas masses from CO luminosities. For a fixed value of alpha_CO, a slope of 1.14+/-0.02 is found. If instead we adopt values of 4.6 and 0.8 for disk galaxies and (U)LIRGs, respectively, we find the two distinct relations. If applying a continuously varying alpha_CO to our sample, we recover a single relation with slope of 1.60+/-0.03. The SFRs is a steeper function of total gas than that of molecular gas, and is tighter among low-luminosity galaxies. We find no correlation between SFRs and atomic gas.

Prediction of thermal resistances and heat conduction of carbon nanotube aerogels in various permeated gases

Heat conduction in single-walled carbon nanotube (SWNT) aerogels is investigated by an off-lattice Monte Carlo method. Thermal boundary resistances (TBRs) between the SWNT and four permeated gases of argon, nitrogen, neon and hydrogen are reported from fitting simulation results with experimental data. It is found that the TBRs between the SWNT and the permeated gases decrease with larger gas molecular masses. Effects of volume fractions and complex morphologies of SWNTs on thermal conductivities of SWNT aerogels are also quantified. The effective thermal conductivities of SWNT aerogels increase with the larger volume fraction, the greater length and the smaller diameter of the SWNTs.

Examination of the thermal accommodation coefficient used in the sizing of iron nanoparticles by time-resolved laser-induced incandescence

While time-resolved laser-induced incandescence (TiRe-LII) shows promise as a diagnostic for sizing aerosolized iron nanoparticles, the spectroscopic and heat transfer models needed to interpret TiRe-LII measurements on iron nanoparticles remain uncertain. This paper focuses on three key aspects of the models: the thermal accommodation coefficient; the spectral absorption efficiency; and the evaporation sub-model. Based on a detailed literature review, spectroscopic and heat transfer models are defined and applied to analyze TiRe-LII measurements carried out on iron nanoparticles formed in water and then aerosolized into monatomic and polyatomic carrier gases. A comparative analysis of the results shows nanoparticle sizes that are consistent between carrier gases and thermal accommodation coefficients that follow the expected trends with bath gas molecular mass and structure.

Effects of molecular adsorption on carrier transport properties of large-size graphene

The temperature dependent resistance and thermoelectric power of macroscopic graphenes are studied in various gas environments. The temperature dependent slope of resistance is weaker in gas environments with heavier molecules. Following the temperature dependent slopes of normalized resistance, one can identify the molecular mass of the environmental gas. This is relative to the atomically sharp potential modification due to adsorbed gas molecules on the graphene. The temperature dependent thermopower increases as the mass of the gas molecules increases. A universal relationship between resistance and thermoelectric power in various gas environments further confirms that the transport mechanism is dominated by the adsorbed gas molecules on the graphene surface.

Evolution of Titan׳s major atmospheric gases and cooling since accretion

This paper discusses two possible pathways of loss of the two main gases from Titan׳s post-accretional atmosphere, methane (CH4) and ammonia (NH3), by the mechanisms of thermal escape and emission from the interior coupled with thermal escape. The results give the decline of initial atmospheric gas masses to their present-day levels of 0.1bar CH4 and 1.4bar N2 (or equivalent 1.7bar NH3, as a precursor of N2). From the published data on planetary and Titan׳s accretion rates, the accretion temperature was estimated as Tac=355 to 300K. In the first 0.5–0.6Myr after accretion, Titan׳s surface cools to 150K and it takes about 5Myr to cool to near its present temperature of 94K. The present-day internal composition corresponds to the accreted Titan made of two solids, antigorite and brucite, that account for 59.5wt%, and an outer shell of an aqueous solution of NH3+(NH4)2SO4 accounting for 40.0wt%, and methane for a much smaller fraction of 0.6wt%. In thermal escape of CH4 and NH3, based on the Maxwell–Boltzmann distribution of gas-molecule velocities, the initial gas mass N0 in the atmosphere is lost by a first-order flux, Nt=N0 exp(−kt), where t is time (yr) and k (yr−1) is a rate parameter that depends on temperature, gas molecular mass, atmosphere thickness, and Titan׳s escape velocity.The computed initial Tac=355K is too high and the two gases would be lost from the primordial atmosphere in several hundred years. However, emissions of CH4 and NH3 from the interior, at reasonable rates that do not deplete the Titan gas inventory and function for periods of different length of time in combination with thermal escape, may result in stable CH4 and NH3 atmospheric masses, as they are at the present. The periods of emissions of different magnitudes of CH4 range from 6×104 to 6×105yr, and those of NH3 are 55,000–75,000yr.At the lower Tac=300K, thermal escape of gases alone allows their atmospheric masses to decrease from the primordial to the present-day levels in 50,000–70,000 years, when Titan׳s temperature has decreased to 245–255K. Below this temperature, the NH3 atmospheric mass is comparable to the present-day N2 mass. Thermal escape does not contradict the existence of the photolytic sink of CH4 in the cooled Titan atmosphere. The thermal escape mechanism does not require arbitrary assumptions about the timing of the start and duration of the gas emissions from the interior.

Thermal-Piezoresistive Resonators and Self-Sustained Oscillators for Gas Recognition and Pressure Sensing

This paper presents experimental and theoretical investigation of the response of microscale dual-plate thermal-piezoresistive resonators (TPRs) and self-sustained oscillators (TPOs) to different gases and pressures. It is demonstrated that the resonant frequency of such devices follow particular trends in response to the changes in the surrounding gas and its pressure. A mathematical model is derived to explain the damping dependent frequency shift characteristic of the TPO. The solution of the model indicates that the stiffness of the actuator beam decreases as the value of the damping coefficient drops at lower gas density caused by the change in the gas molecular mass or pressure. When operated in the TPR mode (linear operation), however, the frequency shift of the same silicon structure is mainly a function of gas thermal conductivity. The two different sensing mechanisms are confirmed by the measurement results showing opposite frequency shift for the TPR and TPO in helium-nitrogen mixtures. In pressure tests, frequency shifts as high as -2300 ppm are measured for a TPO by changing the air pressure from 84 to 43 kPa.

Gas transport through cork: Modelling gas permeation based on the morphology of a natural polymer material

Natural polymers have been studied during the last years for the transport and separation of liquid and gas mixtures, in terms of solubility and permeability data, and their structure and mechanical properties have been characterised. However, no transport models have been reported, relating transport with the material morphology. Cork is a natural cellular material containing three structural polymers (suberin, lignin and polysaccharides). Cork is considered a natural polymer, with economic relevance due to its sealing, non-toxic, stable and low-density properties. Cork was characterised in this work in terms of its solubility and permeability data in relation to various gases with different molecular mass: He, O2, N2, CO2 and 1,1,1,2-tetrafluoroethane (R134a). A morphological analysis of the structure of the cork sample chosen in this work was also performed using SEM (scanning electron microscopy) and TEM (transmission electron microscope) image analysis, which took into account the variation of each relevant structural parameter.A transport model was developed supported on the morphology of cork characterised in this work. The transport model developed considers that gas permeation occurs through the plasmodesmata, which are channels with approximately 100nm of diameter that cross the cell walls of the cork cells. It was found that gas transport follows a Knudsen mechanism, as proved by the gas permeability behaviour with increasing gas molecular mass, with a negligible contribution of viscous transport to the total flux.

Current Sheet Axial Dynamics of 2.5-kJ KSU-DPF Under High-Pressure Regime

In dense plasma focus (DPF) machines, the high-pressure (HP) regime of operation can be used as alternative technique to short-circuit (SC) test as the current sheet motion is minimal. The SC test was performed to get the right values for the static parameters of the machine. HP shots of more than 30 mbar were performed on the 2.5-kJ Kansas State University DPF machine to determine the deviation of HP values from SC values in computed static inductance and resistance. The test was performed using various gases over a wide range of molecular/atomic mass, starting from hydrogen as the lightest gas up to argon. It was found that the deviation in static inductance and resistance computed from HP method is inversely proportional to gas molecular mass at a certain pressure. The heavy gases like neon and argon were found to give the most accurate results. At 60 mbar of argon, the inductance deviation was 6.5%, and the resistance deviation was 14%. It was found also that increasing gas pressure over 30 mbar using heavy gases like Ar or Ne gives no effective improvement on the computed static impedance. Snowplow model was used to predict the axial position and the axial speed of the current sheet during the HP regime. The model showed that the average axial speed in heavy gases like argon was 0.8 cm/ μs, whereas in hydrogen, it was 1.6 cm/μs.

Molecular dynamics simulation of the behaviour of the charged nanodroplet in electrospray

Molecular dynamics simulation method has been used in this Letter to investigate the behaviour of the charged nanodroplet in electrospray ionisation (ESI). The results indicate that: (i) two metastable states of the charged droplet exist after initial fierce fission because of over-charged condition in nitrogen atmosphere; (ii) nitrogen atmosphere accelerates the desolvation procedure, but it cannot lead to complete desolvation; therefore the methods of increasing the gas pressure, relative gas molecular mass and temperature are still needed; (iii) coexistence-area exists in the periphery of the droplet. The value 0.298 was applied to determine the liquid-vapour interface, exceeding which atoms with a local density were assigned to the liquid phase, and then the radius of the droplet was derived.