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resolution, kinetic, emitted, olah, george, klumpp, douglas, 470, 04961, superelectrophiles, lammertsma, koop, rague, schleyer, schwarz, helmut, concert, 1341, anie, 198913211, 1321, angewandte, chemie, edition, anderlan, lukas, jochum, roland, 4418, 22374575, 3350777, 201103432, 2012cheuj, 4411a, 4411, solvation, dimers, 1983, catalyzed, pulsed, flight, probe, 4775, 445276, 1983jchph, 4763t, 4763, callicoatt, berton, förde, kirk, ruchti, jung, lilian, janda, kenneth, halberstadt, nadine, 1998, capture, within, 9371, 476389, 1998jchph, 9371c, kim, jeong, hyun, peterka, darcy, chia, neumark, daniel, 214301, 16774401, 2202313, 2006jchph, 124u4301k, 23090688, 3555426, 201200664, cationic, patterson, 1968, existence, 3625, 1669660, 1968jchph, 3625p, gao, kunqi, hngnh, 144301, 25877572, 4916648, 142n4301g, 142, survey, species, 267, 2004ijmsp, 243g, 243, scheidemann, schilling, toennies, anomalies, j100112a012, 2128, tiangang, xueming, 2020, absolute, 6491, 583, 218552023, 32381705, 1126, abb8020, 2020sci, 582y, 582, higgins, reho, stienkemeier, ernst, lehmann, scoles, 754, 63150, 56800, 8_51, 723, beams, smalley, 1976, excitation, 3276, 432667, 1976jchph, 3266s, 3266, cappelletti, bartocci, alessio, falcinelli, belpassi, leonardo, tarantelli, francesco, pirani, fernando, components, 6240, 25755007, 201406103, 2015cheuj, 6234c, 6234, bergeat, astrid, onvlee, jolijn, naulin, avoird, costes, inelastic, collisions, 353, 25803474, 2066, 149628, 2204, 2015natch, 349b, 349, 12125566, 20867761, 2010phrvl, 105c3001b, 1003, 0948, friedrich, bretislav, 11858, 001m, 0000, 000e, f3c4, 2013phyoj, 42f, fragile, union, elliott, pakes, skrbek, vinen, 2000, capillary, wave, crystallography, crystallization, sheets, 1409, 2000phrvb, 1396e, vyacheslav, igor, nanostructures, 119677151, 0849, 2013jltp, 94g, 1070, 119874763, s1063776111040182, 2011jetp, 1061g, 1061, conductivity, bundles, superconducting, 052605, 4742330, 2012apphl, 101e2605g, vladimirovich, kulish, mikhail, igorevich, 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is bound with an energy of 20 kcal mol this doubly charged ion has been made by accelerating the helium hydride ion to 900 kev and firing it into argon it has a short life of 4 ns 70 h 2 he has been made and could occur in nature via h 2 he h 2 he 70 h 3 he n exists for n from 1 to over 30 and there are also clusters with more hydrogen atoms and helium 73 noble gas edit noble gas cluster ions exist for different noble gases singly charged cluster ions containing xenon exist with the formula he n xe m where n and m 1 74 many different he n kr exist with n between 1 and 17 with higher values possible he n kr 2 and he n kr 3 also exist for many values of n he 12 kr 2 and he 12 kr 3 ions are common these singly charged cluster ions can be made from krypton in helium nanodroplets subject to vacuum ultraviolet radiation 74 the ar argon ion can form many different sized clusters with helium ranging from hear to he 50 ar but the most common clusters are he 12 ar and smaller these clusters are made by capturing an argon atom in a liquid helium nanodroplet and then ionizing with high speed electrons he is formed which can transfer charge to argon and then form a cluster ion when the rest of the droplet evaporates 75 nehe n can be made by ultraviolet photoionization clusters only contain one neon atom the number of helium atoms can vary from 1 to 23 but nehe 4 and nehe 8 are more likely to be observed 74 doubly charged ions of helium with noble gas atoms also exist including arhe 2 krhe 2 and xehe 2 76 metals edit various metal helium ions are known alkali metal helide ions are known for all the alkalis the molecule ground state for the diatomic ions is in the x 1 σ state the bond length gets bigger as the periodic table is descended with lengths of 1 96 2 41 2 90 3 10 and 3 38 å for li he na he k he rb he and cs he the dissociation energies are 1 9 0 9 0 5 0 4 and 0 3 kcal mol showing bond energy decreases when the molecule breaks up the positive charge is never on the helium atom 70 when there are many helium atoms around alkali metal ions can attract shells of helium atoms clusters can be formed from absorbing metal into helium droplets the doped droplets are ionized with high speed electrons for sodium clusters appear with the formula na he n with n from 1 to 26 na he is the most common but na he 2 is very close in abundance na he 8 is much more abundant than clusters with more helium but na 2 he n with n from 1 to 20 also appears na 3 he n with small n is also made for potassium k he n with n up to 28 and k 2 he n for n from 1 to 20 is formed k he and k he 2 are both common and k he 12 is a bit more commonly formed than other similar sized clusters 77 caesium and rubidium cations also form clusters with helium 77 other known metal helium ions include cr he co he co he 3 ni he and ni he 3 70 pthe 2 78 79 formed by high electric field off platinum surface in helium 76 vhe 2 76 herh 2 is decomposed in high strength electric field 80 81 ta 2 he mo 2 he w 2 he re 2 he ir 2 he pt 2 he 2 w 3 he 2 w 3 he 3 and w 3 he 4 70 nonmetals edit hen 2 can form at around 4 k from an ion beam of n 2 into cold helium gas 82 the energy needed to break up the molecule is 140 cm 1 which is quite a bit stronger than the van der waals neutral molecules hen 2 is tough enough to have several vibrational bending and rotational states 83 he n n 2 with n from 2 to 6 have been made by shooting electrons at a supersonically expanding mix of nitrogen and helium 70 c 60 he is formed by irradiating c 60 with 50ev electrons and then steering ions into cold helium gas c 60 he 2 is also known 84 he oh has been detected although it is not produced when hto tritiated water decays 70 he n co has been detected for values of n from 1 to 12 also ch 3 he ochhe and nh 2 he have been detected 70 young and coggiola claimed to make hec by an electric discharge off graphite into helium 85 when tritium substituted methane ch 3 t decays ch 3 he is produced in a very small amount 86 the helium formyl cation hehco is a linear molecule it has a vibrational frequency red shifted 12 4 cm 1 compared to hco it can be considered as a deenergized protonation reaction intermediate for the heh co hco he 83 hehco can be produced by a supersonic expansion of a gas mixture of he co and h 2 which is hit by a cross beam of electrons co and h 2 are only supplied at 1 of the helium 83 the hehn 2 molecule is linear the he h bondlength is 1 72 å it has an infrared band due to b h stretching with a base at 3158 42 cm 1 83 87 the binding energy is 378 cm 1 in the 000 vibrational state and 431 cm 1 in the 100 vibrational state 88 he 2 hn 2 is also known one helium atom is linked to a hydrogen and the other is less tightly bound 88 h 2 o h 2 osf 5 sf 5 and sf 6 can form clusters with varying numbers of helium atoms 89 excimers edit the he 2 excimer is responsible for the hopfield continuum helium also forms an excimer with barium ba he 90 predicted compounds edit predicted solids edit crystal structure of the hypothetical compound mgf 2 he helium in white magnesium in orange and fluorine in blue he h 2 o 2 is predicted to form a solid with orthorhombic structure ibam 91 iron helide fehe was early on claimed to have been found 92 but the discovery was classified as an alloy 53 early studies predicted the fehe exists as an interstitial compound under high pressure 93 perhaps in dense planetary cores 94 or as suggested by freeman dyson in neutron star crust material 95 recent density functional theory calculations predict the formation of fehe compounds at pressures above about 4 tpa 96 suggesting indeed that these compounds could be found inside giant planets white dwarf stars or neutron stars na 2 heo is predicted to have a similar structure to na 2 he but with oxygen atoms in the same position as the electron pair so that it becomes o 2 it would be stable from 13 to 106 gpa 2 this substance could be a way to store helium in a solid 97 la 2 3 x li 3x tio 3 he is a porous lithium ion conduction perovskite that can contain helium like a clathrate 33 helium is predicted to be included under pressure in ionic compounds of the form a 2 b or ab 2 these compounds could include na 2 ohe mgf 2 he over 107 gpa and caf 2 he 30 110 gpa stabilisation occurs by the helium atom positioning itself between the two like charged ions and partially shielding them from each other 98 helium is predicted to form an inclusion compound with silicon si 2 he this has a hexagonal lattice of silicon atoms with helium atoms lined up in the channels it should be formed when liquid silicon is injected with helium at over 1gpa and cooled 99 helium is predicted to form a fluoride he 3 f 2 under extreme pressures well over 1 tpa 100 predicted van der waals molecules edit the beryllium oxide helium adduct hebeo is believed to be bonded much more strongly than a normal van der waals molecule with about 5 kcal mol of binding energy the bond is enhanced by a dipole induced positive charge on beryllium and a vacancy in the σ orbital on beryllium where it faces the helium 101 102 variations on the beryllium oxide adduct include hebe 2 o 2 102 rnbehe including hnbehe ch 3 nbehe 102 ch 4 x nbehe x sih 4 x nbehe x nh 3 x nbehe x ph 3 x nbehe x oh 2 x nbehe x sh 2 x nbehe x 103 and hebe c 5 h 5 104 hydridohelium fluoride hhef is predicted to have a lifetime of 157 femtoseconds with a 5 kcal mol barrier 105 the lifetime of the deuterium isotopomer is predicted to be much longer due to a greater difficulty of tunneling for deuterium 106 this molecule s metastability is slated due to electrostatic attraction between hhe and f which increases the barrier to an exothermic breakup 101 under pressures over 23 gpa hhef should be stable 107 calculations for coinage metal fluorides include hecuf as stable 105 heagf is unstable 105 heauf is predicted 105 and ag 3 he with binding energy 1 4 cm 1 108 ag 4 he binding energy 1 85 cm 1 au 3 he binding energy 4 91 cm 1 108 and au 4 he binding energy 5 87 cm 1 108 henao is predicted calculation for binary van der waals helium molecules include hene li 4 he binding energy 0 008 cm 1 the li 3 he is not stable 108 na 4 he binding energy 0 03 cm 1 the na 3 he is not stable 108 cu 3 he binding energy 0 90 cm 1 108 o 4 he binding energy 5 83 cm 1 108 s 4 he binding energy 6 34 cm 1 108 se 4 he binding energy 6 50 cm 1 108 f 4 he binding energy 3 85 cm 1 108 cl 4 he binding energy 7 48 cm 1 108 br 4 he binding energy 7 75 cm 1 108 i 4 he binding energy 8 40 cm 1 108 n 4 he binding energy 2 85 cm 1 108 p 4 he binding energy 3 42 cm 1 108 as 4 he binding energy 3 49 cm 1 108 bi 4 he binding energy 33 26 cm 1 108 si 4 he binding energy 1 95 cm 1 108 ge 4 he binding energy 2 08 cm 1 108 cah 4 he binding energy 0 96 cm 1 108 nh 4 he binding energy 4 42 cm 1 108 mnh 4 he binding energy 1 01 cm 1 108 ybf 4 he binding energy 5 57 cm 1 108 i 4 2 he or i 3 2 he 109 bonds are predicted to form to nickel with helium as a weak ligand in henico and henin 2 101 heo lif 2 is predicted to form a planar metastable molecule 110 1 tris pyrazolyl borate beryllium and 1 tris pyrazolyl borate magnesium are predicted to bind helium at low temperatures 111 there is also a prediction of a he o bond in a molecule with caesium fluoride or tetramethyl ammonium fluoride 112 lihe 2 is predicted to be in an efimov state when excited 113 predicted ions edit fluoroheliate ion many ions have been investigated theoretically to see if they could exist just about every diatomic cation with helium has been studied for the diatomic dications for stability the second ionization level of the partner atom has to be below the first ionization level of helium 24 6 ev for li f and ne the ground state is repulsive so molecules will not form for n and o the molecule would break up to release he however hebe 2 heb 2 and hec 2 are predicted to be stable also second row elements from na to cl are predicted to have a stable hex 2 ion 70 hey 3 is predicted to be the lightest stable diatomic triply charged ion 114 other possibly thermochemically stable ions include hezr 3 hehf 3 hela 3 hend 3 hece 3 hepr 3 hepm 3 hesm 3 hega 3 hetb 3 hedy 3 heho 3 heer 3 hetm 3 and helu 3 where the third ionization point is below that of helium 70 the positronium helide ion pshe should be formed when positrons encounter helium 115 the fluoroheliate fheo ion should be stable but salts like lifheo are not stable 116 71 hheco theoretical 117 fhes is predicted to be stable 118 fhebn hhen 2 is unlikely to exist 119 hhe oh 2 is probably unstable 120 the lithium hydrohelide cation hlihe is linear in theory this molecular ion could exist with big bang nucleosynthesis elements 121 other hydrohelide cations that exist in theory are hnahe sodium hydrohelide cation hkhe potassium hydrohelide cation hbehe 2 beryllium hydrohelide cation hmghe 2 magnesium hydrohelide cation and hcahe 2 calcium hydrohelide cation 121 hebeo is predicted to have a relatively high binding energy of 25 kcal mol 1 122 similarly the ethynylhelium cation hec ch is predicted to be bound with respect to ethynyl cation and helium by 22 kcal mol however vinylhelium hech ch 2 0 03 kcal mol and methylhelium hech 3 1 5 kcal mol cations are predicted to be bound much more weakly 123 hche 71 hchehe 71 for negative ions the adduct is very weakly bound 70 those studied include hecl hebr hef heo and hes 71 fhes 71 fhese 71 c 7 h 6 he 2 71 c 7 h 6 hehe 2 71 fhecc 71 hheoh 2 71 hhebf 71 henc 71 henn 71 hhenn h he 0 765 å he n bond length 2 077 å decomposition barrier of 2 3 kj mol 71 hhenh 3 is predicted to have a c 3v symmetry and a h he bond length of 0 768 å and he n 1 830 the energy barrier against decomposition to ammonium is 19 1 kj mol with an energy release of 563 4 kj mol cleavage to helium hydride ion and ammonia is predicted to be endothermic requiring 126 2 kj mol 71 discredited or unlikely observations edit numerous researchers attempted to create chemical compounds of helium in the early part of the twentieth century 124 in 1895 l troost and l ouvrard believed they had witnessed a reaction between magnesium vapour and helium and also argon due to the spectrum of helium disappearing from the tube they were passing it through 125 in 1906 w ternant cooke claimed to have noticed a reaction of helium with cadmium or mercury vapour by observing an increase in the density of the vapour zinc vapour did not react with helium 126 j j manley claimed to have found gaseous mercury helide hehg in 1925 127 128 129 hghe 10 130 131 publishing the results in nature but then had trouble finding a stable composition and eventually gave up morrison thought that helium if irradiated so that one electron is pushed to a higher orbit would behave like hydrogen consequently he predicted that radioactive elements might form helides and claimed in 1928 to succeed in forming a compound of helium with lead 214 and a compound of helium with bismuth 214 132 between 1925 and 1940 in buenos aires horacio damianovich studied various metal helium combinations including beryllium behe iron fehe palladium pdhe platinum pt 3 he bismuth and uranium 133 92 to make these substances electrical discharges impacted helium into the surface of the metal 4 later these were demoted from the status of compounds to that of alloys 53 platinum helide pt 3 he was discredited by j g waller in 1960 134 palladium helide pdhe is formed from tritium decay in palladium tritide the helium 3 he is retained in the solid as a solution boomer claimed the discovery of tungsten helide whe 2 as a black solid 135 it is formed by way of an electric discharge in helium with a heated tungsten filament when dissolved in nitric acid or potassium hydroxide tungstic acid forms and helium escapes in bubbles the electric discharge had a current of 5 ma and 1 000 v at a pressure between 0 05 and 0 5 mmhg for the helium the process works slowly at 200 v and 0 02 mmhg of mercury vapour accelerates tungsten evaporation by five times the search for this was suggested by ernest rutherford it was discredited by j g waller in 1960 134 boomer also studied mercury iodine sulfur and phosphorus combinations with helium mercury and iodine helium combinations decomposed around 70 c 136 sulfur and phosphorus helium combinations decomposed around 120 c 136 bismuth dihelide bihe 2 137 138 139 h krefft and r rompe claimed reactions between helium and sodium potassium zinc rubidium indium and thallium 140 references edit cotton f albert wilkinson geoffrey 1966 advanced inorganic chemistry john wiley pp 140 141 1 2 3 4 5 6 7 dong xiao oganov artem r 25 april 2014 stable compound of helium and sodium at high pressure nature chemistry 9 5 440 445 arxiv 1309 3827 bibcode 2017natch 9 440d doi 10 1038 nchem 2716 pmid 28430195 s2cid 20459726 grochala w 1 january 2009 on chemical bonding between helium and oxygen pdf polish journal of chemistry 83 1 87 122 archived from the original abstract on 2 february 2017 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