Infrared Emission Research Articles

Formation and infrared identification of protonated fluoranthene isomers 3-, 9-, and 10-C16H11+ in solid para-H2.

Polycyclic aromatic hydrocarbons (PAH) and their derivatives are prospective carriers of unidentified infrared (UIR) emission features observed in interstellar media. Fluoranthene (C16H10) is a simple planar PAH with five- and six-membered rings; it can be considered as a fragment of C60, which, along with its cationic counterpart, has been identified in interstellar media. Protonated fluoranthene, C16H11+, was generated upon electron bombardment during deposition at 3.2 K of p-H2 containing fluoranthene in a small proportion. The intensities of infrared features of C16H11+ decreased after maintaining the matrix in darkness because of its neutralization with trapped electrons. According to the correlations in intensities upon neutralization and secondary photolysis, observed lines were classified into three groups which are assigned to isomers 3-C16H11+, 9-C16H11+, and 10-C16H11+. Experimental vibrational wavenumbers and relative IR intensities of the features agree with corresponding calculated values predicted for these three isomers of C16H11+ with the B3PW91/6-311++G(2d,2p) method. 3-C16H11+ and 9-C16H11+ are predicted to have the lowest energy (within 5 kJ mol-1), whereas 10- and 1-C16H11+ are lying above the global minimum 3-C16H11+ by ∼20 kJ mol-1. However, definitive identification of 1-C16H11+ could not be made as only the most intense line is tentatively assigned. Although the observed spectra of these isomers match unsatisfactorily with the UIR bands, they will facilitate the potential terrestrial and extraterrestrial identification of these species.

Investigating the Covering Fraction Distribution of Swift/BAT AGNs with X-Ray and Infrared Observations

Abstract We present an analysis of a sample of 69 local obscured Swift/Burst Alert Telescope active galactic nuclei (AGNs) with X-ray spectra from NuSTAR and infrared (IR) spectral energy distributions from Herschel and WISE. We combine this X-ray and IR phenomenological modeling and find a significant correlation between reflected hard X-ray emission and IR AGN emission, with suggestive indications that this correlation may be stronger than the one between intrinsic hard X-ray and IR emissions. This relation between the IR and reflected X-ray emission suggests that both are the result of the processing of intrinsic emission from the corona and accretion disk by the same structure. We explore the resulting implications on the underlying distribution of covering fraction for all AGNs, by generating mock observables for the reflection parameter and IR luminosity ratio using empirical relations found for the covering fraction with each quantity. We find that the observed distributions of the reflection parameter and IR-to-X-ray ratio are reproduced with broad distributions centered around covering fractions of at least ∼40%–50%, whereas narrower distributions match our observations only when centered around covering fractions of ∼70%–80%. Our results are consistent with both independent estimates of the covering fractions of individual objects and the typical covering fraction obtained on the basis of obscured fractions for samples of AGNs. These results suggest that the level of reprocessing in AGNs, including X-ray reflection, is related in a relatively straightforward way to the geometry of the obscuring material.

Even‐Parity Excited States in Infrared Emission, Absorption, and Raman Scattering Spectra of Shallow Donor Centers in Silicon

The Lyman absorption spectra of different shallow dopants in elemental semiconductors at liquid‐helium temperature show typically transitions from the even‐parity ground state to odd‐parity excited states. Such transitions are dipole allowed and observed by absorption spectroscopy. Knowledge on the excited states with other type of symmetry can be derived from absorption and Raman spectra of a heavily doped semiconductor, or at experimental conditions enabling optical dipole‐allowed transitions from or into even‐parity states. Here, we report on the experimental observation of impurity transitions involving different excited even‐parity (ns‐ and nd‐) states in silicon crystals: 1) doped with group‐V hydrogen‐like donors in samples with large infrared absorbance, and 2) doped with the magnesium double donor evoking a thermal population of the lowest even‐parity excited states.

Effect of Cr3+ doping on structural and optical property of ZnGa2O4 synthesized by sol gel method

Zinc gallate host and chromium ions doped ZnGa2O4 nano-powders was synthesized by citric acid assisted sol-gel method. The dopant molar percentage were varied between (0–2.5 mol. %). The x-ray diffraction (XRD) patterns shown that all synthesized nano powders are cubic structured and doping of Cr3+ ions did not affect the structure at all. The scanning electron microscope micrographs show small particles in nano range that are uniformly distributed, but became agglomerated with high doping of chromium concentrations. The high-resolution transmission electron microscope (HR-TEM) image shows the formation of several agglomerated particles with clear grain boundary and different sizes. Energy dispersive x-ray spectroscopy measurements confirm the presence of the expected elements. Ultraviolet–visible spectrophotometer measurement shows the % reflectance in the UV–vis region to be dependents on Cr3+ ions and the estimated band gap was found to vary between 4.46 and 4.80 eV. Un-doped ZnGa2O4 nano powder displays a broad blue emission but doping with Cr3+ ions caused the emission to occur in the near infrared region. An increase in Cr3+ ions up to 2.0 mol% lead to significantly enhancement in the near infra-red (NIR) emission but decrease thereafter. The CIE color coordinates values located in blue and NIR of the spectrum for undoped and Cr3+ doped samples, respectively. The photoluminescence emission intensity was also observed to be dependent on the excitation wavelength and the emission PL spectrum perfectly match the transparency window of living tissues and can effectively be used for bio imaging application.

Ultrapure NIR-to-NIR single band emission of β-PbF2: Yb3+/Tm3+ in glass ceramics

An ultrapure near infrared (NIR) emission entered at 800 nm upon 976 nm laser excitation (NIR-to-NIR) was observed in β-PbF2: Yb3+/Tm3+ glass ceramics (GCs). The ultrapure NIR-to-NIR single band emission originated from the 3H4 → 3H6 transition of Tm3+ with the ratio of NIR emission, and a blue band up to 9633 was obtained. Through detailed analysis of the crystal structure and the energy transfer between Tm3+ and Yb3+, it is elucidated that the host lattice with low phonon energy cooperative with the energy mismatch results in a dramatic population of the 3H4 state as well as ultrapure NIR-to-NIR single band emission. Moreover, up-conversion (UC) emission properties and the decay lifetimes of β-PbF2: Yb3+/Tm3+ in GCs were explored thoroughly. The results illustrate that efficient cross relaxation (CR) processes between Tm3+ generate the energy redistribution in UC emission spectra, further concentrating energy to NIR emission. These two issues can be treated as crucial factors on ultrapure NIR-to-NIR single band emission in β-PbF2: Yb3+/Tm3+ in GCs. The ultrapure NIR-to-NIR single band emission through 976 nm laser excitation is advantageous for enhancing resolution and has potential application in bio-imaging fields.

A flow cytometric analysis of macrophage- nanoparticle interactions in vitro: induction of altered Toll-like receptor expression.

BackgroundNanoparticles exhibit unique physiochemical characteristics that provide the basis for their utilization. The diversity of potential and actual applications compels a thorough understanding regarding the consequences of their containment within the cellular environment.PurposeThis paper presents a flow cytometric examination of the biologic effects associated with the internalization of citrate-buffered silver (Ag) nanoparticles (NP) by the murine macrophage cell line, RAW264.7.Materials and methodsCells were cultured with varying concentrations of citrate-buffered Ag nanoparticle and analyzed for changes in cellular volume, fluorescence emissions, and surface receptor expression.ResultsNotable changes in side scatter (SSC) signal occurred following the phagocytosis of citrate-buffered Ag NP representative of the 10 nm, 50 nm, and 100 nm particle size by cultured RAW 264.7 cells. A characteristic associated with the internalization of all the citrated Ag NP sizes tested, was the detection of emitted infra-red and near-infrared wavelength emissions. This characteristic consistently permitted the detection of 10 nm, 50 nm, and 100 nm Ag NP particles internalized within the RAW cells by flow cytometry. A functional distinction between monocyte subsets within the RAW 264.7 cell line was noted as Ag NP are taken up by the F4/80+ subset of cells within the culture. Further, the internalization of Ag NP by the cells resulted in an increased cell surface expression of the Toll-like receptor (TLR) 3, but not TLR4.ConclusionTaken together, these results implicate the more mature macrophage in the ingestion of Ag NP; and an influence upon at least one of the Toll receptors present in macrophages following exposure to Ag NP. Further, our flow cytometric approach presents a potentially viable detection method for the identification of occult Ag NP material using an indicator cell line.

Field Measurements and Satellite Remote Sensing of Daily Soil Surface Temperature Variations in the Lower Colorado Desert of California

The purpose of this study was to better understand the relationships between diurnal variations of air temperature measured hourly at the soil surface, compared with the thermal infra-red (TIR) emission properties of soil surfaces located in the Lower Colorado Desert of California, eastern Riverside County. Fifty air temperature loggers were deployed in January of 2017 on wooden stakes that were driven into the sandy or rocky desert soils at both Ford Dry Lake and the southern McCoy Mountains wash. The land surface temperature (LST) derived from Landsat satellite images was compared to measured air temperatures at 1 m and at the soil surface on 14 separate dates, until mid-September, 2017. Results showed that it is feasible to derive estimated temperatures at the soil surface from hourly air temperatures, recorded at 1 m above the surface (ambient). The study further correlated Landsat LST closely with site measurements of air and surface temperatures in these solar energy development zones of southern California, allowing inter-conversion with ground-based measurements for use in ecosystem change and animal population biology studies.

Development of a nickel hydroxide nanopetal decorated molecular imprinted polymer based electrode for sensitive detection of epigallocatechin-3-gallate in green tea

Green tea possesses medicinal and therapeutic properties owing to the presence of a large number of catechins in it. Among them, epigallocatechin-3-gallate (EGCG) is the most significant and abundant catechin with a number of health promoting attributes. In this work, a molecularly imprinted polymer (MIP) is combined with Ni(OH)2 nanopetals to facilitate an efficient and selective detection of epigallocatechin-3-gallate (EGCG) in green tea. The Ni(OH)2 nanopetals synthesized using a simple solution route, was homogeneously mixed with the MIP prepared by the co-polymerization of acrylonitrile and ethylene glycol dimethacrylate along with graphite. Material characterizations were performed using powder X-ray diffraction (P-XRD), fourier transform infra-red (FTIR) spectroscope, UV-visible (UV-vis) spectroscope and field emission scanning electron microscope (FESEM), respectively. Considerable improvement in the electrochemical properties of the modified electrode was witnessed over the unmodified counterpart by means of cyclic voltammetry (CV). Differential pulse voltammetry (DPV) results depicted a linear range from 10 μM to 100 μM and limit of detection (LOD) as 7 nM which is eventually the lowest amongst reported literatures.. The electrode demonstrated reasonable analytical characteristics and its performance was also successfully validated with green tea samples using partial least square regression (PLSR) technique and standard addition method.

Far-infrared emission of massive stars

We present results of the analysis of a sample of 22 stars of spectral types from O7 to B5 and luminosity classes I–V for which spectra from the Infrared Spectrograph (IRS) of Spitzer are available. The IRS spectra of these stars are examined for signs of excess infrared (IR) emission by comparison with stellar atmospheric spectra. We find that the spectra of half of the studied stars are dominated by excess emission in the far-IR, including all six super- and bright giants. In order to examine the origin of the far-IR excess, we supplement the Spitzer data with optical high-resolution echelle spectroscopy (λ∕Δλ ~ 105), near-IR high-contrast coronagraphic imaging taken with the SPHERE instrument at VLT with a spatial resolution of 0.′′05, and WISE and Herschel photometry. In the optical region, we detect various absorption and emission lines (H α, C III, and N III) irrespective of the far-IR excess. Pfund α and Humphrey α lines are observed at the same time as the far-IR excess. These lines are stronger in stars with far-IR excess than in stars without excess. A scattered-light disk in the central r ≲ 2.5′′ region of the far-IR excess stars HD 149404, HD 151804, and HD 154368 can be excluded from H band imaging down to a 1σ contrast of F(r)∕F∗~ 10−6. The far-IR excess is fit either by a free–free component from ionized gas as for the winds of hot stars or a large (1 pc) circumstellar dust shell. The putative dust envelopes required to explain the excess have a visual extinction as low as a few hundred μ-mag.

'Corrigendum: Role of Ni2+(d8) ions in electrical, optical and magnetic properties of CdS nanowires for optoelectronic and spintronic applications (2018 Nanotechnology 29 265602)'.

For the first time, 1D Ni ions doped CdS nanowires (NWs) were synthesized via chemical vapour deposition (CVD). The synthesized Cd0.886Ni0.114S NWs were single crystalline. We have reported here, investigation of optical, electrical and magnetic properties of prepared NWs for optoelectronic and spintronic applications. Successful incorporation of Ni ions in an individual CdS NW has been confirmed through several characterization tools: significant higher angle and phonon modes shift were observed in the XRD and Raman spectra. SEM-EDX and XPS analysis also confirmed the presence of Ni2+ ions. Room-temperature photoluminescence (RT-PL) showed multi-peaks: two emission peaks in the visible region centered at 517.1 nm (green), 579.2 nm (orange), and a broad-band near infrared (NIR) emission centered at 759.9 nm. Herein, the first peak showed 5 nm red-shift upon Ni2+ doping hinting the formation of exciton magnetic polarons (EMPs), and broad-NIR emission was observed in both chlorides and bromides which was assigned to d-d transition of Ni ions whose energy levels lie at 749.51 nm (13342 cm-1) and 750.98 nm (13316 cm-1) are very close to NIR emission. Orange emission was not only remained at same peak position but also its PL intensity significantly enhanced at 78 K and is assigned to d-d transition (3A2g → 1Eg) of Ni2+ ions. It was observed that 11.4% Ni2+ ions doping enhance the conductivity of our sample around 20 times and saturation magnetization (Ms) increases from 7.2 × 10-5 Am2/Kg to 1.17 × 10-4 Am2/Kg which shows promise for optoelectronic and spintronic applications.

Experimental verification of agglomeration effects in infrared spectra on micron-sized particles

Context. Detailed analysis of observed infrared (IR) dust emission spectra is often performed in order to derive information about mineralogy, particle size, and temperature of the dust. However, the IR bands are also influenced by agglomeration of the dust particles. Light scattering theory simulating agglomeration and growth effects is especially challenged by the consideration of highly absorbing particles. Aims. To clarify the influence of agglomeration on the diagnostic phonon bands of amorphous SiO2 particles, we experimentally measure the extinction spectra of systematically arranged particle configurations and compare the measured spectra with the spectra obtained from different theoretical approaches. Methods. We construct artificial particle agglomerates by means of the dedicated robotic manipulation (DRM) technique. IR microspectroscopic extinction measurements of these arranged particles are performed at the French National Synchrotron Facility, SOLEIL, in the mid-IR region considering polarization effects. The theoretical approaches applied are the discrete dipole approximation (DDA) as well as T-matrix and finite-difference time-domain methods. Results. In both the experimental spectra and the theoretical calculations, we find that the Si–O stretching vibration band at about 9 μm is clearly broadened on the long-wavelength side by the agglomeration of particles. This is mainly caused by the radiation components, which are polarized in directions in which the agglomerate is extended, while the extinction band profile of the component polarized perpendicular to the long axis of an elongated agglomerate is close to the spectrum of the single sphere. All of the theoretical simulations predict these effects in qualitatively good agreement. Conclusions. Our comparative study of the experimentally measured and theoretically calculated IR extinction spectra of well-defined agglomerate structures makes obvious how the various particle arrangements in small clusters might contribute to average spectra of dust. Therefore the study might help to improve the precision of light scattering calculations as well as their specific applicability.

Preparation of TiO2 nanoparticles by hydrolysis of TiCl4 using water and glycerol solvent system

The anatase phase TiO2 nanoparticles (NPs) were synthesized by precipitation method using TCl4 as a precursor in a new reaction medium containing water and glycerol. The as-synthesized photocatalysts were characterized by Raman spectroscopy, Fourier Transform Infra-red Spectroscopy (FT-IR), UV-Visible spectroscopy and Field Emission Scanning Electron Microscopy (FESEM). The Raman spectra indicate the formation of crystalline anatase phase TiO2 NPs after calcination at 300 and 4000C. TiO2 NPs formation was confirmed by observing the major characteristic, FT-IR vibration bands of Ti-O network. The band gap calculated from UV-Vis DRS spectra ranged from 3.02-3.28 eV. FESEM images exhibit spherical shape TiO2 NPs in the form of nano-clusters with crystallite sizes ranged from 9.5026.14 nm. FESEM images show that as the calcination temperature increases, the sizes of the TiO2 NPs also increase. The inclusion of glycerol promotes the formation of smaller particles and lowers the band gap of TiO2 NPs.

Luminomagnetic Nd3+ doped fluorapatite coated Fe3O4 nanostructures for biomedical applications

AbstractLuminomagnetic nanostructured Nd3+ doped fluorapatite (FAP) coated Fe3O4 nanoparticles were produced by hydrothermal method. X‐ray diffraction analysis indicates that the prepared nanoparticles contain both FAP and Fe3O4 phases. Electron microscope analysis shows the formation of nanoparticles of Fe3O4 encased in rod shaped FAP nanoparticles of average length 40 nm. Magnetic measurements confirm the room temperature superparamagnetic nature of the nanoparticles with saturation magnetization value up to 7.8 emu/g. The prepared nanoparticles display strong near infrared (NIR) emission at 1060 nm under 800 nm excitation. Cell viability studies for 72 hour demonstrate the survival rate of over 84% with 500 μg/mL concentration indicating the good cytocompatibility of the prepared materials. The present Nd3+ doped FAP coated Fe3O4 nanostructure provides an excellent multifunctional platform for diagnostics and therapeutic applications.

Fully anharmonic infrared cascade spectra of polycyclic aromatic hydrocarbons.

The infrared (IR) emission of polycyclic aromatic hydrocarbons (PAHs) permeates our universe; astronomers have detected the IR signatures of PAHs around many interstellar objects. The IR emission of interstellar PAHs differs from their emission as seen under conditions on Earth as they emit through a collisionless cascade down through their excited vibrational states from high internal energies. The difficulty in reproducing interstellar conditions in the laboratory results in a reliance on theoretical techniques. However, the size and complexity of PAHs require careful consideration when producing the theoretical spectra. In this work, we outline the theoretical methods necessary to lead to fully theoretical IR cascade spectra of PAHs including: an anharmonic second order vibrational perturbation theory treatment, the inclusion of Fermi resonances through polyads, and the calculation of anharmonic temperature band shifts and broadenings (including resonances) through a Wang-Landau approach. We also suggest a simplified scheme to calculate vibrational emission spectra that retain the essential characteristics of the full IR cascade treatment and can directly transform low temperature absorption spectra in IR cascade spectra. Additionally we show that past astronomical models were in error in assuming a 15 cm-1 correction was needed to account for anharmonic emission effects.

Discovery of Extended Infrared Emission around the Neutron Star RXJ0806.4–4123* †

Abstract Following up on a faint detection of a near-infrared (NIR) source at the position of the X-ray thermal isolated neutron star RX J0806.4–4123, we present new Hubble Space Telescope observations in the H-band. The NIR source is unambiguously detected with a Vega magnitude of 23.7 ± 0.2 (flux density of 0.40 ± 0.06 μJy at λ = 1.54 μm). The source position is coincident with the neutron star position, and the implied NIR flux is strongly in excess of what one would expect from an extrapolation of the optical-UV spectrum of RX J0806.4–4123. The NIR source is extended, with a size of at least 0.″8, and shows some asymmetry. The conservative upper limit on the flux contribution of a point source is 50%. Emission from gas and dust in the ambient diffuse interstellar medium can be excluded as a cause for the extended emission. The source parameters are consistent with an interpretation as either the first NIR-only detected pulsar wind nebula or the first resolved disk around an isolated neutron star.

Near-infrared emitting Ca5 (PO4 )3 Cl:Eu2+ ,Nd3+ phosphor for modification of the solar spectrum.

Intense near-infrared (NIR) emitting phosphors Ca5 (PO4 )3 Cl:Eu2+ ,Nd3+ were synthesized using a conventional solid-state reaction method and characterized using X-ray diffraction, reflectance, photoluminescence (PL) emission and PL excitation (PLE) spectroscopy, and PL lifetime measurements. The emission could be excited by broad band radiation in the nUV region as a consequence of Eu2+ →Nd3+ energy transfer. The efficiency of Eu2+ →Nd3+ energy transfer was as high as 80.8%. Two components observed in the decay curves could be identified with Eu2+ substituting different Ca2+ sites. Eu2+ lifetimes were shortened after Nd3+ doping. Near infra-red emission intensity was limited by Nd3+ →Nd3+ energy transfer and the consequent concentration quenching. The critical distance for Nd3+ →Nd3+ energy transfer was estimated to be 11.41Å. Absorption of nUV radiations followed by conversion to NIR indicated the potential application in solar photovoltaics.

Sm3+-Doped Molybdenum Gadolinium Borate Glasses for Orange Emission Laser Active Medium

Room temperature visible and near infrared optical absorption and emission spectra of Sm3+-doped molybdenum gadolinium borate (MGB) glasses with molar composition 25MoO3-20Gd2O3–(55 − x)B2O3−xSm2O3 (x = 0.05, 0.1, 0.5, 1.0, 2.0 mol.%) have been analyzed. The experimental oscillator strengths of absorption bands have been used to determine the Judd–Ofelt (J–O) parameters. Fluorescence spectra were recorded by exciting the samples at 402 nm. Using the J–O parameters and luminescence data, the radiative transition probabilities (AR), branching ratios (BR), and stimulated emission cross-sections oe) are obtained. The decay curves of the 4G5/2 - 6H7/2 transition exhibit a non-exponential curve fit for all concen-trations. The concentration quenching has been attributed to the energy transfer through the cross-relaxation between Sm3+ ions. 4G5/2 level and its relative quantum efficiencies are measured. Intense reddish-orange emission corresponding to the 4G5/2−6H7/2 transition has been observed in these glasses at the 487-nm excitation, From the values of the radiative parameters, it is concluded that the 1.0-mol% Sm3+-doped MGB glass may be used as a laser active medium with the emission wavelength at 599 nm. The analysis of the non-exponential behavior of decay curves through the Inokuti–Hirayama model indicates that the energy transfer between Sm3+ ions is of dipole–dipole type. The quantum efficiency for the 4G5/2 level of MGBSm10 glass is found to be 67%. The co-related color temperature obtained from CIE (Commission International de L’Eclairage) for these glass samples is ∼1620 K for the indicated orange emission at the 402-nm excitation.

Infrared Spectrum of Protonated Corannulene H+C20H10 in Solid para-Hydrogen and its Potential Contribution to Interstellar Unidentified Infrared Bands

Polycyclic aromatic hydrocarbons (PAH) and their derivatives, including protonated and cationic species, are suspected to be carriers of the unidentified infrared (UIR) emission bands observed from the galactic and extragalactic sources. We extended our investigations of infrared (IR) spectra of protonated planar PAH to a nonplanar PAH, corannulene (C20H10), which is regarded as a fragment of a fullerene, C60. The protonated corannulene H+C20H10 was produced on bombarding a mixture of corannulene and para-hydrogen (p-H2) with electrons during deposition at 3.2 K. During maintenance of the electron-bombarded matrix in darkness the intensities of IR lines of protonated corannulene decreased because of neutralization by electrons that were slowly released from the trapped sites. The observed lines were classified into two groups according to their responses to secondary irradiation at 365 nm. Eighteen lines in one group are assigned to the lowest-energy species among five possible isomers, hub-H+C20H10, and ...

Anharmonic vibrational eigenfunctions and infrared spectra from semiclassical molecular dynamics.

We describe a new approach based on semiclassical molecular dynamics that allows simulating infrared absorption or emission spectra of molecular systems with inclusion of anharmonic intensities. This is achieved from semiclassical power spectra by computing first the vibrational eigenfunctions as a linear combination of harmonic states, and then the oscillator strengths associated with the vibrational transitions. We test the approach against a 1D Morse potential and apply it to the water molecule with results in excellent agreement with discrete variable representation quantum benchmarks. The method does not require any grid calculations, and it is directly extendable to high dimensional systems. The usual exponential scaling of the basis set size with the dimensionality of the system can be avoided by means of an appropriate truncation scheme. Furthermore, the approach has the advantage to provide IR spectra beyond the harmonic approximation without losing the possibility of an intuitive assignment of absorption peaks in terms of normal modes of vibration.

Origin of the infra-red emission peak in freezing water

When droplets of purified water (1–5 μl) were cooled from the bottom, they slowly and continuously supercooled before releasing latent heat as a transient burst of infra-red (IR) radiation. In order to determine the role of this IR emission, a thin rectangular water layer was cooled unilaterally while imaged from above by an infrared (FLIR) camera. The first noticeable event was an IR burst that rapidly (< 0.1 s) moved through a 5-mm-long path of water. Final solidification of the water layer was recognized by an increase in volume, as the meniscus at the air interface changed from concave to convex. The propagation of the IR burst through the water layer preceded the first visible onset of volume increase and solidification by more than one second. The transient and early appearance of the IR burst belongs to what is called the first stage of freezing. This stage has been linked to the formation of so-called spongy ice. Both IR burst and pinnately shaped spongy ice appear at the same time and share a short transient existence. It is only this early type of ice that is associated with the IR burst. By contrast, the later-occurring solid ice formation parallels a diminishing IR emission.