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Wednesday, November 26, 2014

Spectroscopy

From Wikipedia, the free encyclopedia
 
Analysis of white light by dispersing it with a prism is an example of spectroscopy.

Spectroscopy /spɛkˈtrɒskəpi/ is the study of the interaction between matter and radiated energy.[1][2] Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, by a prism. Later the concept was expanded greatly to comprise any interaction with radiative energy as a function of its wavelength or frequency. Spectroscopic data is often represented by a spectrum, a plot of the response of interest as a function of wavelength or frequency.

Introduction

Spectroscopy and spectrography are terms used to refer to the measurement of radiation intensity as a function of wavelength and are often used to describe experimental spectroscopic methods. Spectral measurement devices are referred to as spectrometers, spectrophotometers, spectrographs or spectral analyzers.

Daily observations of color can be related to spectroscopy. Neon lighting is a direct application of atomic spectroscopy. Neon and other noble gases have characteristic emission frequencies (colors). Neon lamps use collision of electrons with the gas to excite these emissions. Inks, dyes and paints include chemical compounds selected for their spectral characteristics in order to generate specific colors and hues. A commonly encountered molecular spectrum is that of nitrogen dioxide. Gaseous nitrogen dioxide has a characteristic red absorption feature, and this gives air polluted with nitrogen dioxide a reddish brown color. Rayleigh scattering is a spectroscopic scattering phenomenon that accounts for the color of the sky.

Spectroscopic studies were central to the development of quantum mechanics and included Max Planck's explanation of blackbody radiation, Albert Einstein's explanation of the photoelectric effect and Niels Bohr's explanation of atomic structure and spectra. Spectroscopy is used in physical and analytical chemistry because atoms and molecules have unique spectra. As a result, these spectra can be used to detect, identify and quantify information about the atoms and molecules. Spectroscopy is also used in astronomy and remote sensing on earth. Most research telescopes have spectrographs. The measured spectra are used to determine the chemical composition and physical properties of astronomical objects (such as their temperature and velocity).

Theory

One of the central concepts in spectroscopy is a resonance and its corresponding resonant frequency. Resonances were first characterized in mechanical systems such as pendulums. Mechanical systems that vibrate or oscillate will experience large amplitude oscillations when they are driven at their resonant frequency. A plot of amplitude vs. excitation frequency will have a peak centered at the resonance frequency. This plot is one type of spectrum, with the peak often referred to as a spectral line, and most spectral lines have a similar appearance.

In quantum mechanical systems, the analogous resonance is a coupling of two quantum mechanical stationary states of one system, such as an atom, via an oscillatory source of energy such as a photon. The coupling of the two states is strongest when the energy of the source matches the energy difference between the two states. The energy (E) of a photon is related to its frequency (\nu) by E = h\nu where h is Planck's constant, and so a spectrum of the system response vs. photon frequency will peak at the resonant frequency or energy. Particles such as electrons and neutrons have a comparable relationship, the de Broglie relations, between their kinetic energy and their wavelength and frequency and therefore can also excite resonant interactions.

Spectra of atoms and molecules often consist of a series of spectral lines, each one representing a resonance between two different quantum states. The explanation of these series, and the spectral patterns associated with them, were one of the experimental enigmas that drove the development and acceptance of quantum mechanics. The hydrogen spectral series in particular was first successfully explained by the Rutherford-Bohr quantum model of the hydrogen atom. In some cases spectral lines are well separated and distinguishable, but spectral lines can also overlap and appear to be a single transition if the density of energy states is high enough.

Classification of methods

Spectroscopy is a sufficiently broad field that many sub-disciplines exist, each with numerous implementations of specific spectroscopic techniques. The various implementations and techniques can be classified in several ways.

Type of radiative energy

Types of spectroscopy are distinguished by the type of radiative energy involved in the interaction. In many applications, the spectrum is determined by measuring changes in the intensity or frequency of this energy. The types of radiative energy studied include:

Nature of the interaction

Types of spectroscopy can also be distinguished by the nature of the interaction between the energy and the material. These interactions include:[1]
  • Absorption occurs when energy from the radiative source is absorbed by the material. Absorption is often determined by measuring the fraction of energy transmitted through the material; absorption will decrease the transmitted portion.
  • Emission indicates that radiative energy is released by the material. A material's blackbody spectrum is a spontaneous emission spectrum determined by its temperature. Emission can also be induced by other sources of energy such as flames or sparks or electromagnetic radiation in the case of fluorescence.
  • Elastic scattering and reflection spectroscopy determine how incident radiation is reflected or scattered by a material. Crystallography employs the scattering of high energy radiation, such as x-rays and electrons, to examine the arrangement of atoms in proteins and solid crystals.
  • Impedance spectroscopy studies the ability of a medium to impede or slow the transmittance of energy. For optical applications, this is characterized by the index of refraction.
  • Inelastic scattering phenomena involve an exchange of energy between the radiation and the matter that shifts the wavelength of the scattered radiation. These include Raman and Compton scattering.
  • Coherent or resonance spectroscopy are techniques where the radiative energy couples two quantum states of the material in a coherent interaction that is sustained by the radiating field. The coherence can be disrupted by other interactions, such as particle collisions and energy transfer, and so often require high intensity radiation to be sustained. Nuclear magnetic resonance (NMR) spectroscopy is a widely used resonance method and ultrafast laser methods are also now possible in the infrared and visible spectral regions.

Type of material

Spectroscopic studies are designed so that the radiant energy interacts with specific types of matter.

Atoms

Atomic spectroscopy was the first application of spectroscopy developed. Atomic absorption spectroscopy (AAS) and atomic emission spectroscopy (AES) involve visible and ultraviolet light. These absorptions and emissions, often referred to as atomic spectral lines, are due to electronic transitions of outer shell electrons as they rise and fall from one electron orbit to another. Atoms also have distinct x-ray spectra that are attributable to the excitation of inner shell electrons to excited states.

Atoms of different elements have distinct spectra and therefore atomic spectroscopy allows for the identification and quantitation of a sample's elemental composition. Robert Bunsen and Gustav Kirchhoff discovered new elements by observing their emission spectra. Atomic absorption lines are observed in the solar spectrum and referred to as Fraunhofer lines after their discoverer. A comprehensive explanation of the hydrogen spectrum was an early success of quantum mechanics and explained the Lamb shift observed in the hydrogen spectrum led to the development of quantum electrodynamics.

Modern implementations of atomic spectroscopy for studying visible and ultraviolet transitions include flame emission spectroscopy, inductively coupled plasma atomic emission spectroscopy, glow discharge spectroscopy, microwave induced plasma spectroscopy, and spark or arc emission spectroscopy. Techniques for studying x-ray spectra include X-ray spectroscopy and X-ray fluorescence (XRF).

Molecules

The combination of atoms into molecules leads to the creation of unique types of energetic states and therefore unique spectra of the transitions between these states. Molecular spectra can be obtained due to electron spin states (electron paramagnetic resonance), molecular rotations, molecular vibration and electronic states. Rotations are collective motions of the atomic nuclei and typically lead to spectra in the microwave and millimeter-wave spectral regions; rotational spectroscopy and microwave spectroscopy are synonymous. Vibrations are relative motions of the atomic nuclei and are studied by both infrared and Raman spectroscopy. Electronic excitations are studied using visible and ultraviolet spectroscopy as well as fluorescence spectroscopy.

Studies in molecular spectroscopy led to the development of the first maser and contributed to the subsequent development of the laser.

Crystals and extended materials

The combination of atoms or molecules into crystals or other extended forms leads to the creation of additional energetic states. These states are numerous and therefore have a high density of states. This high density often makes the spectra weaker and less distinct, i.e., broader. For instance, blackbody radiation is due to the thermal motions of atoms and molecules within a material. Acoustic and mechanical responses are due to collective motions as well.

Pure crystals, though, can have distinct spectral transitions and the crystal arrangement also has an effect on the observed molecular spectra. The regular lattice structure of crystals also scatters x-rays, electrons or neutrons allowing for crystallographic studies.

Nuclei

Nuclei also have distinct energy states that are widely separated and lead to gamma ray spectra. Distinct nuclear spin states can have their energy separated by a magnetic field, and this allows for NMR spectroscopy.

Other types

Other types of spectroscopy are distinguished by specific applications or implementations:

Applications

UVES is a high-resolution spectrograph on the Very Large Telescope.[9]

History

The history of spectroscopy began with Isaac Newton's optics experiments (1666–1672). Newton applied the word "spectrum" to describe the rainbow of colors that combine to form white light and that are revealed when the white light is passed through a prism. During the early 1800s, Joseph von Fraunhofer made experimental advances with dispersive spectrometers that enabled spectroscopy to become a more precise and quantitative scientific technique. Since then, spectroscopy has played and continues to play a significant role in chemistry, physics and astronomy.
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Tuesday, November 25, 2014

List of interstellar and circumstellar molecules

From Wikipedia, the free encyclopedia

This is a list of molecules that have been detected in the interstellar medium and circumstellar envelopes, grouped by the number of component atoms. The chemical formula is listed for each detected compound, along with any ionized form that has also been observed.

Detection

The molecules listed below were detected by spectroscopy. Their spectral features are generated by transitions of component electrons between different energy levels, or by rotational or vibrational spectra. Detection usually occurs in radio, microwave, or infrared portions of the spectrum.[1]
Interstellar molecules are formed by chemical reactions within very sparse interstellar or circumstellar clouds of dust and gas. Usually this occurs when a molecule becomes ionized, often as the result of an interaction with a cosmic ray. This positively charged molecule then draws in a nearby reactant by electrostatic attraction of the neutral molecule's electrons. Molecules can also be generated by reactions between neutral atoms and molecules, although this process is generally slower.[2] The dust plays a critical role of shielding the molecules from the ionizing effect of ultraviolet radiation emitted by stars.[3]

History

The first carbon-containing molecule detected in the interstellar medium was the methylidyne radical (CH) in 1937.[4] From the early 1970s it was becoming evident that interstellar dust consisted of a large component of more complex organic molecules, probably polymers. Chandra Wickramasinghe proposed the existence of polymeric composition based on the molecule formaldehyde (H2CO).[5] Fred Hoyle and Chandra Wickramasinghe later proposed the identification of bicyclic aromatic compounds from an analysis of the ultraviolet extinction absorption at 2175A.,[6] thus demonstrating the existence of polycyclic aromatic hydrocarbon molecules in space.

In 2004, scientists reported[7] detecting the spectral signatures of anthracene and pyrene in the ultraviolet light emitted by the Red Rectangle nebula (no other such complex molecules had ever been found before in outer space). This discovery was considered a confirmation of a hypothesis that as nebulae of the same type as the Red Rectangle approach the ends of their lives, convection currents cause carbon and hydrogen in the nebulae's core to get caught in stellar winds, and radiate outward.[8] As they cool, the atoms supposedly bond to each other in various ways and eventually form particles of a million or more atoms. The scientists inferred[7] that since they discovered polycyclic aromatic hydrocarbons (PAHs) — which may have been vital in the formation of early life on Earth — in a nebula, by necessity they must originate in nebulae.[8]

In 2010, fullerenes (or "buckyballs") were detected in nebulae.[9] Fullerenes have been implicated in the origin of life; according to astronomer Letizia Stanghellini, "It's possible that buckyballs from outer space provided seeds for life on Earth."[10]

In October 2011, scientists found using spectroscopy that cosmic dust contains complex organic matter ("amorphous organic solids with a mixed aromatic-aliphatic structure") that could be created naturally, and rapidly, by stars.[11][12][13] The compounds are so complex that their chemical structures resemble the makeup of coal and petroleum; such chemical complexity was previously thought to arise only from living organisms.[11] These observations suggest that organic compounds introduced on Earth by interstellar dust particles could serve as basic ingredients for life due to their surface-catalytic activities.[14][15] One of the scientists suggested that these compounds may have been related to the development of life on Earth and said that, "If this is the case, life on Earth may have had an easier time getting started as these organics can serve as basic ingredients for life."[11]

In August 2012, astronomers at Copenhagen University reported the detection of a specific sugar molecule, glycolaldehyde, in a distant star system. The molecule was found around the protostellarbinary IRAS 16293-2422, which is located 400 light years from Earth.[16][17] Glycolaldehyde is needed to form ribonucleic acid, or RNA, which is similar in function to DNA. This finding suggests that complex organic molecules may form in stellar systems prior to the formation of planets, eventually arriving on young planets early in their formation.[18]

In September 2012, NASA scientists reported that PAHs, subjected to interstellar medium (ISM) conditions, are transformed, through hydrogenation, oxygenation, and hydroxylation, to more complex organics — "a step along the path toward amino acids and nucleotides, the raw materials of proteins and DNA, respectively".[19][20] Further, as a result of these transformations, the PAHs lose their spectroscopic signature which could be one of the reasons "for the lack of PAH detection in interstellar ice grains, particularly the outer regions of cold, dense clouds or the upper molecular layers of protoplanetary disks."[19][20]

In June 2013, PAHs were detected in the upper atmosphere of Titan, the largest moon of the planet Saturn.[21]

In 2013, Dwayne Heard at the University of Leeds suggested[22] that quantum mechanical tunneling could explain a reaction his group observed taking place, at a significantly higher than expected rate, between cold (around 63 Kelvin) hydroxyl and methanol molecules, apparently bypassing intramolecular energy barriers which would have to be overcome by thermal energy or ionization events for the same rate to exist at warmer temperatures. The proposed tunneling mechanism may help explain the common observation of fairly complex molecules (up to tens of atoms) in interstellar space.

A particularly large and rich region for detecting interstellar molecules is Sagittarius B2 (Sgr B2). This giant molecular cloud lies near the center of the Milky Way galaxy and is a frequent target for new searches. About half of the molecules listed below were first found near Sgr B2, and nearly every other molecule has since been detected in this feature.[23] A rich source of investigation for circumstellar molecules is the relatively nearby star CW Leonis (IRC +10216), where about 50 compounds have been identified.[24]

Molecules

The following tables list molecules that have been detected in the interstellar medium, grouped by the number of component atoms. If there is no entry in the Molecule column, only the ionized form has been detected. For molecules where no designation was given in the scientific literature, that field is left empty. Mass is given in Atomic mass units. The total number of unique species, including distinct ionization states, is listed in parentheses in each section header.

Most of the molecules detected so far are organic. Only one inorganic species has been observed in molecules which contain at least five atoms, SiH4.[25] Larger molecules have so far all had at least one carbon atom, with no N-N or O-O bonds.[25]
Carbon monoxide is frequently used to trace the distribution of mass in molecular clouds.[26]

Diatomic (43)

Molecule Designation Mass Ions
AlCl Aluminium monochloride[27][28] 62.5 —
AlF Aluminium monofluoride[27][29] 46 —
AlO Aluminium monoxide[30] 43 —
— Argon hydride[31][32] 41 ArH+
C2 Diatomic carbon[33][34] 24 —
— Fluoromethylidynium 31 CF+[35]
CH Methylidyne radical[36] 13 CH+[37]
CN Cyanogen radical[27][36][38][39] 26 CN+,[40] CN-[41]
CO Carbon monoxide[27][42][43] 28 CO+[44]
CP Carbon monophosphide[39] 43 —
CS Carbon monosulfide[27] 44 —
FeO Iron(II) oxide[45] 82 —
H2 Molecular hydrogen[46] 2 —
HCl Hydrogen chloride[47] 36.5 HCl+[48]
HF Hydrogen fluoride[49] 20 —
HO Hydroxyl radical[27] 17 OH+[50]
KCl Potassium chloride[27][28] 75.5 —
NH Nitrogen monohydride[51][52] 15 —
N2 Molecular nitrogen[53][54] 28 —
NO Nitric oxide[55] 30 NO+[40]
NS Nitrogen sulfide[27] 46 —
NaCl Sodium chloride[27][28] 58.5 —
— Magnesium monohydride cation 25.3 MgH+[40]
NaI Sodium iodide[56] 150 —
O2 Molecular oxygen[57] 32 —
PN Phosphorus nitride[58] 45 —
PO Phosphorus monoxide[59] 47 —
SH Sulfur monohydride[60] 33 SH+[61]
SO Sulfur monoxide[27] 48 SO+[37]
SiC Carborundum[27][62] 40 —
SiN Silicon mononitride[27] 42 —
SiO Silicon monoxide[27] 44 —
SiS Silicon monosulfide[27] 60 —
TiO Titanium oxide[63] 63.9 —
The H3+ cation is one of the most abundant ions in the universe. It was first detected in 1993.[2][64]

Triatomic (41)

Molecule Designation Mass Ions
AlNC Aluminium isocyanide[27] 53 —
AlOH Aluminium hydroxide[65] 44 —
C3 Tricarbon[34] 36 —
C2H Ethynyl radical[27][38] 25 —
C2O Dicarbon monoxide[66] 40 —
C2S Thioxoethenylidene[67] 56 —
C2P —[68] 55 —
CO2 Carbon dioxide[69] 44 —
FeCN Iron cyanide[70] 82 —
— Protonated molecular hydrogen 3 H3+[2][64]
H2C Methylene radical[33] 14 —
— Chloronium 37.5 H2Cl+[71]
H2O Water[72] 18 H2O+[73]
HO2 Hydroperoxyl[74] 33 —
H2S Hydrogen sulfide[27] 34 —
HCN Hydrogen cyanide[27][38][75] 27 —
HNC Hydrogen isocyanide[76] 27 —
HCO Formyl radical[77] 29 HCO+[37][77][78]
HCP Phosphaethyne[79] 44 —
— Thioformyl 45 HCS+[37][78]
HNC Hydrogen isocyanide[80] 27 —
— Diazenylium 29 HN2+[78]
HNO Nitroxyl[81] 31 —
— Isoformyl 29 HOC+[38]
KCN Potassium cyanide[27] 65 —
MgCN Magnesium cyanide[27] 50 —
MgNC Magnesium isocyanide[27] 50 —
NH2 Amino radical[82] 16 —
— — 29 N2H+[37][83]
N2O Nitrous oxide[84] 44 —
NaCN Sodium cyanide[27] 49 —
NaOH Sodium hydroxide[85] 40 —
OCS Carbonyl sulfide[86] 60 —
O3 Ozone[87] 48 —
SO2 Sulfur dioxide[27][88] 64 —
c-SiC2 c-Silicon dicarbide[27][62] 52 —
SiCN Silicon carbonitride[89] 54 —
SiNC [90] 54 —
TiO2 Titanium dioxide[63] 79.9 —
Formaldehyde is an organic molecule that is widely distributed in the interstellar medium.[91]

Four atoms (26)

Molecule Designation Mass Ions
CH3 Methyl radical[92] 15 —
l-C3H Propynylidyne[27][93] 37 l-C3H+[94]
c-C3H Cyclopropynylidyne[95] 37 —
C3N Cyanoethynyl[33] 50 C3N−[68]
C3O Tricarbon monoxide[93] 52 —
C3S Tricarbon sulfide[27][67] 68 —
— Hydronium 19 H3O+[96]
C2H2 Acetylene[97] 26 —
H2CN methylene amidogen[98] 28 H2CN+[37]
H2CO Formaldehyde[99] 30 —
H2CS Thioformaldehyde[100] 46 —
HCCN —[101] 39 —
— Protonated hydrogen cyanide 28 HCNH+[78]
— Protonated carbon dioxide 45 HOCO+[102]
HCNO Fulminic acid[103] 43 —
HOCN Cyanic acid[104] 43 —
HOOH Hydrogen peroxide[105] 34 —
HNCO Isocyanic acid[88] 43 —
HNCS Isothiocyanic acid[106] 59 —
NH3 Ammonia[27][107] 17 —
HSCN Thiocyanic acid[108] 59 —
SiC3 Silicon tricarbide[27]  64 —
HMgNC Hydromagnesium isocyanide[109]  51.3 —
Methane, the primary component of natural gas, has also been detected on comets and in the atmosphere of several planets in the Solar System.[110]

Five atoms (19)

Molecule Designation Mass Ions
C5 Linear C5[34]  60 —
— Ammonium Ion[111][112]  18 NH4+
CH4 Methane[51][97] 16 —
CH3O Methoxy radical[113] 31 —
c-C3H2 Cyclopropenylidene[38][114][115] 38 —
l-H2C3 Propadienylidene[115] 38 —
H2CCN Cyanomethyl[citation needed] 40 —
H2C2O Ketene[88] 42 —
H2CNH Methylenimine[116] 29 —
HNCNH Carbodiimide[117] 42 —
— Protonated formaldehyde 31 H2COH+[118]
C4H Butadiynyl[27] 49 C4H–[119]
HC3N Cyanoacetylene[27][38][78][115][120] 51 —
HCC-NC Isocyanoacetylene[121] 51 —
HCOOH Formic acid[115] 46 —
NH2CN Cyanamide[122] 42 —
HC(O)CN Cyanoformaldehyde[123] 55 —
SiC4 Silicon-carbide cluster[62] 92 —
SiH4 Silane[124] 32 —
In the ISM, formamide (above) can combine with methylene to form acetamide.[125]

Six atoms (15)

Molecule Designation Mass Ions
c-H2C3O Cyclopropenone[125] 54 —
E-HNCHCN E-Cyanomethanimine[126] 54 —
C2H4 Ethylene[97] 28 —
CH3CN Acetonitrile[88][127] 40 —
CH3NC Methyl isocyanide[127] 40 —
CH3OH Methanol[88] 32 —
CH3SH Methanethiol[106] 48 —
l-H2C4 Diacetylene[27][128] 50 —
— Protonated cyanoacetylene 52 HC3NH+[78]
HCONH2 Formamide[125] 44 —
C5H Pentynylidyne[27][67] 61 —
C5N Cyanobutadiynyl radical[129] 74 —
HC2CHO Propynal[130] 54 —
HC4N —[27]  63 —
CH2CNH Ketenimine[114] 40 —
Acetaldehyde (above) and its isomers vinyl alcohol and ethylene oxide have all been detected in interstellar space.[131]

Seven atoms (9)

Molecule Designation Mass Ions
c-C2H4O Ethylene oxide[132] 44 —
CH3C2H Methylacetylene[38] 40 —
H3CNH2 Methylamine[133] 31 —
CH2CHCN Acrylonitrile[88][127] 53 —
H2CHCOH Vinyl alcohol[131] 44 —
C6H Hexatriynyl radical[27][67] 73 C6H–[115][134]
HC4CN Cyanodiacetylene[88][120][127] 75 —
CH3CHO Acetaldehyde[27][132] 44 —
The radio signature of acetic acid, a compound found in vinegar, was confirmed in 1997.[135]

Eight atoms (11)

Molecule Designation Mass
H3CC2CN Methylcyanoacetylene[136] 65
H2COHCHO Glycolaldehyde[137] 60
HCOOCH3 Methyl formate[88][115][137] 60
CH3COOH Acetic acid[135] 60
H2C6 Hexapentaenylidene[27][128] 74
CH2CHCHO Propenal[114] 56
CH2CCHCN Cyanoallene[114][136] 65
CH3CHNH Ethanimine[138] 43
C7H Heptatrienyl radical[139] 85
NH2CH2CN Aminoacetonitrile[140] 56
(NH2)2CO Urea[141] 60

Nine atoms (10)

Molecule Designation Mass Ions
CH3C4H Methyldiacetylene[142] 64 —
CH3OCH3 Dimethyl Ether[143] 46 —
CH3CH2CN Propionitrile[27][88][115][127] 55 —
CH3CONH2 Acetamide[114][125] 59 —
CH3CH2OH Ethyl Alcohol[144] 46 —
C8H Octatetraynyl radical[145] 97 C8H–[146]
HC7N Cyanohexatriyne or Cyanotriacetylene[27][107][147][148] 99 —
CH3CHCH2 Propylene (propene)[149] 42 —
CH3CH2SH Ethyl mercaptan[150] 62 —
Diacetylene, HCCCCH
Methyldiacetylene, HCCCCCH3
Cyanotetraacetylene, HCCCCCCCCCN
A number of polyyne-derived chemicals are among the heaviest molecules found in the interstellar medium.

Ten or more atoms (15)

Atoms Molecule Designation Mass Ions
10 (CH3)2CO Acetone[88][151] 58 —
10 (CH2OH)2 Ethylene glycol[152][153] 62 —
10 CH3CH2CHO Propanal[114] 58 —
10 CH3C5N Methyl-cyano-diacetylene[114] 89 —
10 (CH3)2CHCN Isopropyl cyanide[154][155] 69 —
11 HC8CN Cyanotetra-acetylene[27][147] 123 —
11 C2H5OCHO Ethyl formate[156] 74 —
11 CH3COOCH3 Methyl acetate[157] 74 —
11 CH3C6H Methyltriacetylene[114][142] 88 —
12 C6H6 Benzene[128] 78 —
12 C3H7CN n-Propyl cyanide[156] 69 —
13 HC10CN Cyanodecapentayne[147] 147 —
13 HC11N Cyanopentaacetylene[147] 159 —
60 C60 Buckminsterfullerene
(C60 fullerene)[158]		 720 C60+[159][160]
70 C70 C70 fullerene[158] 840 —

Deuterated molecules (17)

These molecules all contain one or more deuterium atoms, a heavier isotope of hydrogen.
Atoms Molecule Designation
2 HD Hydrogen deuteride[161][162]
3 H2D+, HD2+ Trihydrogen cation[161][162]
3 HDO, D2O Heavy water[163][164]
3 DCN Hydrogen cyanide[165]
3 DCO Formyl radical[165]
3 DNC Hydrogen isocyanide[165]
3 N2D+ —[165] 
4 NH2D, NHD2, ND3 Ammonia[162][166][167]
4 HDCO, D2CO Formaldehyde[162][168]
5 NH3D+ Ammonium ion[169][170]
7 CH2DCCH, CH3CCD Methylacetylene[171][172]

Unconfirmed (10)

Evidence for the existence of the following molecules has been reported in scientific literature, but the detections are either described as tentative by the authors, or have been challenged by other researchers. They await independent confirmation.
Atoms Molecule Designation
2 SiH Silylidine[76]
4 PH3 Phosphine[173]
5 H2NCO+ -[174]
10 H2NH2CCOOH Glycine[38][175]
12 CO(CH2OH)2 Dihydroxyacetone[176]
12 C2H5OCH3 Ethyl methyl ether[177]
18 C10H8+ Naphthalene cation[178]
24 C24 Graphene[179]
24 C14H10 Anthracene[7][180]
26 C16H10 Pyrene[7]
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