Appearance energies of hydrogen and deuterium cluster ions

Abstract

Electron ionization cross sections for hydrogen and deuterium clusters have been measured near the threshold energy with a high-resolution electron impact ionization mass spectrometer. Appearance energies are reported for odd-sized H+n and D+n cluster ions for sizes n ⩽ 11.

Formation of even-numbered hydrogen cluster cations in ultracold helium droplets

“…32 Another, more technical problem is the presence of deuterium; clusters H n−2 D + with an odd number of atoms may easily be mistaken for even-numbered H n + because both have the same nominal mass, n Da. An analogous problem applies to experiments with deuterium clusters contaminated with traces of 1 H. 27,28 In the present study we were able to use a highresolution mass spectrometer to identify even-numbered H n + up to n = 120. Two factors made this possible: First, the high mass resolution easily distinguishes H n + from most background ions, helium cluster ions, and mixed He x H y + .…”

“…30 Thus, the Penning ionization as well as charge transfer from He + contribute to the H 6 + ion yield. Direct ionization of hydrogen clusters would feature a lower onset because the adiabatic ionization energy of H 2 is only 15.428 eV; 27,30 its contribution is below the detection limit. This observation agrees with experiments on other clusters embedded in helium droplets which show that direct ionization is extremely inefficient.…”

“…20 When free hydrogen clusters are ionized by electrons or photons, one observes predominantly odd-numbered cluster ions H n + . [21][22][23][24][25][26][27][28] The low intensity of even-numbered H n + arises from the large exothermicity of the reaction H 2 + + H 2 → H 3 + + H, ͑1͒…”

Study on $H_3^+$ Formation by Synchrotron Radiation

“…3 ion was first found by Thomson in 1912 [1]. Subsequently, a lot of experimental and theoretical works have been devoted to the study of hydrogen clusters since they are perhaps the simplest example of molecular clusters [2][3][4][5][6][7][8][9][10][11][12]. It has established that H + 3 is a very stable molecule having an equilateral triangular structure [3].…”

“…Given all this interest it is not surprising that H + 3 has been the subject of numerous theoretical and experimental studies [2,10,11]. However, the details of the mechanism for H + 3 formation from neutral clusters are still unclear and the appearance energy of H + 3 is also controversial [11,12]. The H + 3 ion can be usually generated by two methods.…”