Infrared spectroscopy of the protonated nitrogen dimer: The complexity of shared proton vibrations

Abstract

The proton-bridged dimers of nitrogen, e.g., N2–H+–N2 and N2–D+–N2, are produced in a pulsed-discharge supersonic nozzle source, mass selected in a reflectron time-of-flight spectrometer, and studied with infrared photodissociation spectroscopy using the method of messenger atom tagging with argon. Both complexes are studied from 700–4000 cm−1. These spectra reproduce the high frequency vibrations seen previously but discover many new vibrational bands, particularly those in the region of the shared proton modes. Because of the linear structure of the core ions, simple vibrational spectra are expected containing only the antisymmetric N–N stretch and two lower frequency modes corresponding to proton stretching and bending motions. However, many additional bands are detected corresponding to various combination bands in this system activated by anharmonic couplings of the proton motions. The anharmonic coupling is stronger for the H+ system than it is for the D+ system. Using anharmonic proton vibrations computed previously and combinations of computed harmonic frequencies, reasonable assignments can be made for the spectra of both isotopomers. However, advanced anharmonic computational treatments are needed for this system to confirm these assignments.

Characterizing the Intramolecular H-bond and Secondary Structure in Methylated GlyGlyH+ with H2 Predissociation Spectroscopy

“…The former is conspicuously absent in the experimental spectrum while the observed bands near 1400 cm -1 appear significantly weaker than the calculated intensity of the H-bonded mode. The absence of these bands is readily explained by the anharmonicity associated with strongly shared protons in a variety of contexts [51][52][53][54][55], and is explicitly addressed in the context of all four systems in the Anharmonicity of the Intramolecular H-bond section.…”

Ab initio anharmonic vibrational frequency predictions for linear proton-bound complexes OC–H+–CO and N2–H+–N2

“…It is well known that both anions and cations in the gas phase can form strongly bound molecular complexes with neutral species, the structure and dynamics of which are relevant to issues from ion solvation to interstellar chemistry. [1][2][3][4][5][6][7][8][9][10][11][12][13] Infrared spectroscopy has served as a particularly important source of quantitative insight into the structure and dynamics of such ion complexes, sampled by high resolution direct laser absorption 9,[14][15][16][17][18][19][20][21][22][23] as well as vibrational predissociation methods. [4][5][6][7]10,[24][25][26] Indeed, the past decade has witnessed remarkable advances in the field of molecular ion spectroscopy, in part aided by the development of powerful ion trapping and Ar tagging techniques as well as extension of table top pulsed IR laser sources out past the traditional H stretching (2-4 mm) into the fingerprint (4-15 mm) region.…”

An Argon–Oxygen Covalent Bond in the ArOH+ Molecular Ion

“…However, we did manage to collect spectra for the 18 Oi sotopologues (Supporting Information, Figures S3, S4). [37] This gives us further confidence in our assignments. We can also exclude contributions from ions isobaric to OH + such as NH 3 + or CH 5 + (m/z = 17), [36] or isobaric to ArOH + such as N 4 H + and C 2 O 2 H + (that is, protonated N 2 or CO dimers; m/z = 57), because their spectra are known.…”