أيون هيدريد الهليوم

أيون هيدريد الهليوم

الأسماء
اسم أيوپاك النظامي Hydridohelium(1+)
المُعرِّفات
رقم CAS
3D model (JSmol)	Interactive image
ChEBI	CHEBI:33688 CHEBI:33689 neutral excimer
ChemSpider	21106447 Y
مرجع Gmelin	2
CompTox Dashboard (EPA)	DTXSID801018818
InChI InChI=1S/HHe/h1H/q+1 Y Key: HSFAAVLNFOAYQX-UHFFFAOYSA-N Y
SMILES [HeH+]
الخصائص
الصيغة الجزيئية	HHe
كتلة مولية	5.01 g mol-1
ما لم يُذكر غير ذلك، البيانات المعطاة للمواد في حالاتهم العيارية (عند 25 °س [77 °ف]، 100 kPa).
مراجع الجدول

أيون هيدريد الهليوم او أيون هيدرو-هليوم (1+)، هو أيون كاتيون بشحنة إيجابية صيغته الكيميائية HeH⁺. يتألف جزيئه من ذرة هليوم مرتبطة بذرة هيدروجين، مع إزالة إلكترون واحد. وهو أخف الأيونات النووية المغايرة، ويمكن مقارنته بأيون جزيء الهيدروجين، H+2.

أُنتج الأيون لأول مرة في المعمل عام 1925. وهو مستقر عند العزل، لكنه شديد التفاعل، ولا يمكن تحضيره بكميات كبيرة لأنه سيتفاعل مع أي جزيء آخر ملامس له. وهو في الحقيقة أقوى حمض معروف. كان يعتقد بيتواجده في الأوساط البين نجمية منذ السبعينيات، وتم التحقق من هذا أخيراً عام 2019.

 الخصائص الفيزيائية

على اليمين، تركيب أيون الهيدرين الهليوم، يسار، السديم الكوكبي NGC 7027.

إن أيون هيدريد الهيليوم ⁺HHe يوجد فقط في الحالة الغازية ولا يمكن تحضيره في الحالة الصلبة الكثيفة، حيث أنه سيعمل على برتنة أي أنيون أو جزيء أو ذرة عند التماس معها.

 الجزيء الطبيعي

على عكس أيون هيدريد الهليوم، فإن جزيء هيدريد الهليوم الطبيعي HeH غير مستقر في حالته الأرضية. ومع ذلك، فإنه موجوداً في حالة إثارة على هيئة إكسيمر (HeH*)، ورُصد طيفه لأول مرة في منتصف الثمانينيات.

دخل الجزيء الطبيعي لأول مرة في قاعدة گملين.

 الخصائص والتفاعلات الكيميائية

 الحمضية

رغم ذلك فإن قيم الحموضة في الوسط السائل هي حسابية حسب قانون هس:

HHe+(g)	→	H+(g)	+ He(g)	+178 ك.ج/مول
HHe+(aq)	→	HHe+(g)		+973 kJ/mol
H+(g)	→	H+(aq)		– 1530 kJ/mol
He(g)	→	He(aq)		+19 ك.ج/مول
HHe+(aq)	→	H+(aq)	+ He(aq)	– 360 ك.ج/مول

إن طول الرابطة التساهمية في أيون ⁺HeH يبلغ 0.772 أنگستروم.

 التاريخ

يعتبر أيون هيدريد الهيليوم أول جزيء نشأ في الكون قبل 13 مليار سنة. وظل العلماء يبحثون عنه في الكون وكان العثور عليه صعبا واحتاج سنوات طويلة في الرصد والبحث.

في أبريل 2019 استطاعت مجموعة من الباحثين من معهد ماكس بلانك لعلم الفلك الراديوي ببون رصد أيونات هيدريد الهيليوم في أحد السدم الكوكبية يبعد عنا نحو 3000 سنة ضوئية.

 Discovery in ionization experiments

Hydridohelium(1+), specifically [4
He1
H]⁺, was first detected indirectly in 1925 by T. R. Hogness and E. G. Lunn. They were injecting protons of known energy into a rarefied mixture of hydrogen and helium, in order to study the formation of hydrogen ions like H+ , H+2 and H+3. They observed that H+3 appeared at the same beam energy (16 eV) as H+2, and its concentration increased with pressure much more than that of the other two ions. From these data, they concluded that the H+2 ions were transferring a proton to molecules that they collided with, including helium.

In 1933, K. Bainbridge used mass spectrometry to compare the masses of the ions [4
He1
H]⁺ (helium hydride ion) and [2
H
21
H]⁺ (twice-deuterated trihydrogen ion) in order to obtain an accurate measurement of the atomic mass of deuterium relative to that of helium. Both ions have 3 protons, 2 neutrons, and 2 electrons. He also compared [4
He2
H]⁺ (helium deuteride ion) with [2
H
3]⁺ (trideuterium ion), both with 3 protons and 3 neutrons.

 Early theoretical studies

The first attempt to compute the structure of the HeH⁺ ion (specifically, [4
He1
H]⁺) by quantum mechanical theory was made by J. Beach in 1936. Improved computations were sporadically published over the next decades.

 Tritium decay methods in chemistry

H. Schwartz observed in 1955 that the decay of the tritium molecule T
2 = 3
H
2 should generate the helium hydride ion [3
HeT]⁺ with high probability.

In 1963, F. Cacace at the Sapienza University of Rome conceived the decay technique for preparing and studying organic radicals and carbenium ions. In a variant of that technique, exotic species like methanium are produced by reacting organic compounds with the [3
HeT]⁺ that is produced by the decay of T
2 that is mixed with the desired reagents. Much of what we know about the chemistry of [HeH]⁺ came through this technique.

 Implications for neutrino mass experiments

In 1980, V. Lubimov (Lyubimov) at the ITEP laboratory in Moscow claimed to have detected a mildly significant rest mass (30 ± 16) eV for the neutrino, by analyzing the energy spectrum of the β decay of tritium. The claim was disputed, and several other groups set out to check it by studying the decay of molecular tritium T 2. It was known that some of the energy released by that decay would be diverted to the excitation of the decay products, including [3
HeT]⁺; and this phenomenon could be a significant source of error in that experiment. This observation motivated numerous efforts to precisely compute the expected energy states of that ion in order to reduce the uncertainty of those measurements. Many have improved the computations since then, and now there is quite good agreement between computed and experimental properties; including for the isotopologues [4
He2
H]⁺, [3
He1
H]⁺, and [3
He2
H]⁺.

 Spectral predictions and detection

In 1956, M. Cantwell predicted theoretically that the spectrum of vibrations of that ion should be observable in the infrared; and the spectra of the deuterium and common hydrogen isotopologues ([3
HeD]⁺ and [3
He1
H]⁺) should lie closer to visible light and hence easier to observe. The first detection of the spectrum of [4
He1
H]⁺ was made by D. Tolliver and others in 1979, at wavenumbers between 1,700 and 1,900 cm⁻¹. In 1982, P. Bernath and T. Amano detected nine infrared lines between 2,164 and 3,158 waves per cm.

 Interstellar space

HeH⁺ has been conjectured since the 1970s to exist in the interstellar medium. Its first detection, in the nebula NGC 7027, was reported in an article published in the journal Nature in April 2019.

 التواجد الطبيعي

 من اضمحلال التريتيوم

The helium hydride ion is formed during the decay of tritium in the molecule HT or tritium molecule T₂. Although excited by the recoil from the beta decay, the molecule remains bound together.

 الوسط بين الكواكب

It is believed to be the first compound to have formed in the universe, and is of fundamental importance in understanding the chemistry of the early universe. This is because hydrogen and helium were almost the only types of atoms formed in Big Bang nucleosynthesis. Stars formed from the primordial material should contain HeH⁺, which could influence their formation and subsequent evolution. In particular, its strong dipole moment makes it relevant to the opacity of zero-metallicity stars. HeH⁺ is also thought to be an important constituent of the atmospheres of helium-rich white dwarfs, where it increases the opacity of the gas and causes the star to cool more slowly.

HeH⁺ could be formed in the cooling gas behind dissociative shocks in dense interstellar clouds, such as the shocks caused by stellar winds, supernovae and outflowing material from young stars. If the speed of the shock is greater than about 90 kilometres per second (56 mi/s), quantities large enough to detect might be formed. If detected, the emissions from HeH⁺ would then be useful tracers of the shock.

Several locations had been suggested as possible places HeH⁺ might be detected. These included cool helium stars, H II regions, and dense planetary nebulae, like NGC 7027, where, in April 2019, HeH⁺ was reported to have been detected.

 انظر أيضاً

• Argonium
• Dihydrogen cation
• Trihydrogen cation

 المصادر

 المراجع

Unless otherwise stated, numerical data are taken from the CRC Handbook of Chemistry and Physics (1981).