Structure of Protonated Carbon Dioxide Clusters:  Infrared Photodissociation Spectroscopy and ab Initio Calculations

Abstract

The infrared photodissociation spectra (IRPD) in the 700 to 4000 cm(-1) region are reported for H+ (CO2)n clusters (n = 1-4) and their complexes with argon. Weakly bound Ar atoms are attached to each complex upon cluster formation in a pulsed electric discharge/supersonic expansion cluster source. An expanded IRPD spectrum of the H+ (CO2)Ar complex, previously reported in the 2600-3000 cm(-1) range [Dopfer, O.; Olkhov, R.V.; Roth, D.; Maier, J.P. Chem. Phys. Lett. 1998, 296, 585-591] reveals new vibrational resonances. For n = 2 to 4, the vibrational resonances involving the motion of the proton are observed in the 750 to 1500 cm(-1) region of the spectrum, and by comparison to the predictions of theory, the structure of the small clusters are revealed. The monomer species has a nonlinear structure, with the proton binding to the lone pair of an oxygen. In the dimer, this nonlinear configuration is preserved, with the two CO2 units in a trans configuration about the central proton. Upon formation of the trimer, the core CO2 dimer ion undergoes a rearrangement, producing a structure with near C2v symmetry, which is preserved upon successive CO2 solvation. While the higher frequency asymmetric CO2 stretch vibrations are unaffected by the presence of the weakly attached Ar atom, the dynamics of the shared proton motions are substantially altered, largely due to the reduction in symmetry of each complex. For n = 2 to 4, the perturbation due to Ar leads to blue shifts of proton stretching vibrations that involve motion of the proton mostly parallel to the O-H+-O axis of the core ion. Moreover, proton stretching motions perpendicular to this axis exhibit smaller shifts, largely to the red. Ab initio (MP2) calculations of the structures, complexation energies, and harmonic vibrational frequencies are also presented, which support the assignments of the experimental spectra.

Infrared spectroscopy of the acetyl cation and its protonated ketene isomer

“…This structure has the argon binding on the OH group, which should cause a significant shift in the O-H stretch. 35,37,[44][45][46] Consistent with this, theory without the Ar predicts the O-H stretch at 3379 cm −1 , corresponding to a 326 cm −1 red shift. This behavior is, therefore, consistent with assignment of the 3045 cm −1 band to the O-H stretch of protonated ketene.…”

“…[28][29][30][31][32][33][34][35][36][37][38][39] Other studies have examined small organic ions containing oxygen, such as HCO + , protonated methanol, protonated ethanol, and protonated formaldehyde. [40][41][42][43][44][45][46] Throughout this work, infrared spectroscopy has been complemented by computational chemistry to investigate stable ion structures and the possible occurrence of isomers.…”

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.…”

Influence of external electric fields on oxygen vacancies at the anatase (101) surface

“…Analogous structures were found in the case of protonated CO 2 dimer. 35 The quintet state structure is non-planar in contrast to the planar structures found for singlet and triplet with the dihedral angle of 50.3 • between O-O-H planes. The CASSCF prediction, structure VII, has no symmetry whereas the RCCSD result, structure VIII, belongs to the C 2 point group with the dihedral angle of 56.2 • .…”