|
| Section2 = }} The hydrohelium(1+) cation, HeH+, also known as the helium hydride ion or helium-hydride molecular ion, is a positively charged ion formed by the reaction of a proton with a helium atom in the gas phase, first produced in the laboratory in 1925. It is isoelectronic with molecular hydrogen. It is the strongest known acid, with a proton affinity of 177.8 kJ/mol. It has been suggested that HeH+ should occur naturally in the interstellar medium, but it has not yet been detected. It is the simplest heteronuclear ion, and is comparable with the hydrogen molecular ion, . Unlike , however, it has a permanent dipole moment, which makes its spectroscopic characterization easier. ==Properties== HHe+ cannot be prepared in a condensed phase, as it would protonate any anion, molecule or atom with which it were associated. However it is possible to estimate a ''hypothetical'' aqueous acidity using Hess's law: A free energy change of dissociation of –360 kJ/mol is equivalent to a p''K''a of –63. The length of the covalent bond in HeH+ is 0.772 Å. Other helium hydride ions are known or have been studied theoretically. , which has been observed using microwave spectroscopy, has a calculated binding energy of 25.1 kJ/mol, while has a calculated binding energy of 0.42 kJ/mol.〔F.Pauzat and Y. Ellinger (Where do noble gases hide in space? ), Astrochemistry: Recent Successes and Current Challenges, Poster Book IAU Symposium No. 231, 2005 A. J. Markwick-Kemper (ed.)〕 The dihelium hydride cation is formed by the reaction of dihelium cation with molecular hydrogen: He2+ + H2 → He2H+ + H·. He2H+ is a linear ion with hydrogen in the centre. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Helium hydride ion」の詳細全文を読む スポンサード リンク
|