Bihalide anions

BrDBr -Ar (b) from 620 to 1680 cm . The depletion of the parent ion signal is shown (gray trace and gray shaded-area) and compared to the eigenvalues (black bars) from a variational calculation on a two-dimensional CCSD(T)/aug-cc-pVTZ-based potential 

Parent ion depletion spectra for BrHI -Ar and BrDI -Ar are shown in Fig. 3.4. Compared to the IR spectra of the symmetric bihalides, these spectra are considerably more complex and their assignment, based on previous calculations [41], was problematic. The two most intense peaks in both spectra correspond closely to the peaks seen in the previous matrix works. Their frequencies exhibit red-shifts when going from the gas phase to the matrix from 12 to 64 cm i. All these peaks were assigned to the type I structure in the matrix. No peaks assigned to type II anions are observed in the gas phase, but additional peaks are observed in the gas phase spectra. In order to reach a satisfactory assignment of all the peaks observed 

Interestingly, four (compared to two in Fig. 3.6) O-H stretching bands were observed in the IR-PD spectrum of the H5OJ H2 complex ]49]. Based on a comparison with computed vibrational frequencies, it was concluded that the perturbation exerted by H2, which is bound by less than 4 kcal moh, is already sufficient to break the symmetry and stabilizes an asymmetric H20- -H30+ structure, for which four O-H bands are predicted. 

The observed bands are more than twenty times broader than the bandwidth of the laser radiation (-5-15 cm i). The increased width could be caused by vibrational hot-bands, but these should be largely eliminated in the spectra because the ions are collisionally cooled prior to interaction with the laser pulse. However, the zero-point motion of the central proton on the extremely flat PES likely extends over an unusually large area, leading to the exploration of a much larger part of 

There have been a number of calculations recently on the vibrations of H5OJ beyond the harmonic approximation. As noted already, such calculations are essential due to the highly anharmonic nature of these vibrations. Attempts to go beyond the harmonic approximation have been done in reduced dimensionality [27, 56] and also with the additional vibrational adiabatic approximation [56], These calculations selected the three proton degrees of freedom and the OO-stretch as the reduced dimensionality space. While such approaches are better in 

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B. S. Ault, Acc. Chem. Res. 15, 103 (1982). Matrix Isolation Investigation of the Hydrogen Bihalide Anions. 

Hydrogen Stretching Band Positions for the Hydrogen Bihalide Anions... 

D. The Bihalide Ions HXjj. —Spectroscopic observations on these species have been made, but there are a number of interesting and unresolved questions which theoretical calculations should be able to clarify. Matrix-isolation studies are in disagreement as to whether vacuum-u.v. photolysis of HC1 in an argon matrix produces C1HC1 or the C1HC1- anion.394... 

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