Chemical probing spectroscopy of H3+ above the barrier to linearity

Abstract

We have performed chemical probing spectroscopy of H + 3 ions trapped in a cryogenic 22-pole ion trap. The ions were buffer-gas cooled to ∼ 55 K by collisions with helium and argon. Excitation to states above the barrier to linearity was achieved by a Ti:Sa laser operated between 11 300 and 13 300 cm −1 . Subsequent collisions of the excited H + 3 ions with argon lead to the formation of ArH + ions that were detected by a quadrupole mass spectrometer with high sensitivity. We report the observation of 17 previously unobserved transitions to states above the barrier to linearity.Comparison to theoretical calculations suggests that the transition strengths of some of these lines are more than five orders of magnitude smaller than those of the fundamental band, which renders them -to the best of our knowledge -the weakest H + 3 transitions observed to date.

How can a 22-pole ion trap exhibit ten local minima in the effective potential?

“…Multipole radiofrequency ion traps [1], in particular the 22-pole ion trap [2], are versatile devices used in laser spectroscopy [3,4,5,6,7,8,9,10] and investigations of chemical reaction processes [2,11,12,13] of atomic and molecular ions. High order multipole traps offer a large field free region in the trap center, and therefore provide a reduced interaction time of the ions with the oscillating electric field compared to a quadrupole trap [14].…”

Communications: Development and characterization of a source of rotationally cold, enriched para-H3+

“…The reason for this decrease is not understood at present but could have an impact on Ar-H 3 + action spectroscopy schemes. [23][24][25] Despite this, there was an increase in the para-H 3 + fraction when H 2 was diluted to ϳ1% in argon.…”

Communication: Visible line intensities of the triatomic hydrogen ion from experiment and theory

“…The development of action spectroscopy in a cryogenic radiofrequency (RF) ion trap provided measurements in the near-IR range 19 and showed great promise for attaining much higher sensitivity than absorption spectroscopy. We have recently extended the range of this method up to almost 17 000 cm −1 .…”

“…9 The measurement of line intensities in the VIS region has, however, been out of reach until now. As described previously, 9,19,20 H + 3 ions were stored in a multipole RF ion trap and buffer-gas cooled with He (2×10 14 cm −3 ) to ∼ 85 K. About 85% of the H + 3 ions thus populated the two lowest rotational (J = 1) levels of the vibrational ground state, having ortho and para symmetries. The near-VIS to VIS transitions were measured by chemical probing with Ar (1 × 10 12 cm −3 ).…”

“…After irradiation, the ion cloud was released into a mass spectrometer (MS) that could be set to either ArH + or H + 3 detection from one 300 ms storage cycle to the next. The ions were counted on a Daly stamp with a scintillator and a photomultiplier detection system 19,21 that is sensitive enough to single-ion count the low ArH + and the high H + 3 (normalization) ion numbers.…”