The adiabatic ionization energy of hydrogen peroxide (HOOH) is investigated, both by means of theoretical calculations and theoretically assisted reanalysis of previous experimental data. Values obtained by three different approaches: 10.638 ± 0.012 eV (purely theoretical determination), 10.649 ± 0.005 eV (reanalysis of photoelectron spectrum), and 10.645 ± 0.010 eV (reanalysis of photoionization spectrum) are in excellent mutual agreement. Further refinement of the latter two values to account for asymmetry of the rotational profile of the photoionization origin band leads to a reduction of 0.007 ± 0.006 eV, which tends to bring them into even closer alignment with the purely theoretical value. Detailed analysis of this fundamental quantity by the Active Thermochemical Tables approach, using the present results and extant literature, gives a final estimate of 10.641 ± 0.006 eV.

Structural studies of a three-component assembly—a host and two distinct guests—were carried out using a combination of 11B and 1H NMR. In aprotic solvent, the imino group that forms ortho to the boronic acid or boronate ester group can form a dative N–B bond. In protic solvent, a molecule of solvent inserts between the nitrogen and boron atoms, partially ionizing the solvent molecule. Additionally, 11B NMR was used in combination with a seventh-order polynomial to calculate five binding constants for each of the individual steps in protic solvent. Comparison of these binding constants was used to establish positive cooperativity in the binding of the two guests.

The electronic and vibrational absorption spectra of the radical anion and cation of p-benzoquinone (PBQ) in an Ar matrix between 500 and 40000 cm−1 are presented and discussed in detail. Of particular interest is the radical cation, which shows very unusual spectroscopic features that can be understood in terms of vibronic coupling between the ground and a very low-lying excited state. The infrared spectrum of PBQ˙+ exhibits a very conspicuous and complicated pattern of features above 1900 cm−1 that is due to this electronic transition, and offers an unusually vivid demonstration of the effects of vibronic coupling in what would usually be a relatively simple region of the electromagnetic spectrum associated only with vibrational transitions. As expected, the intensities of most of the IR transitions leading to levels that couple the ground to the very low-lying first excited state of PBQ˙+ increase by large factors upon ionization, due to “intensity borrowing” from the D0 → D1 electronic transition. A notable exception is the antisymmetric CO stretching vibration, which contributes significantly to the vibronic coupling, but has nevertheless quite small intensity in the cation spectrum. This surprising feature is rationalized on the basis of a simple perturbation analysis.

The Ã2E″← 2A′2 absorption spectrum exhibits vibronically allowed transitions from the ground state of NO3 to upper state levels having a″1 and e′ vibronic symmetries. This paper explores the coupling mechanisms that lend intensities to these features. While transitions to e′ vibronic levels borrow intensity from the very strong 2E′← 2A′2 electronic transition, those to a″1 levels involve only negligible upper-state borrowing effects. Rather, it is the vibronic mixing of the ground vibronic level of NO3 with vibrational levels in the 2E′ electronic state that permit the a″1 levels to be seen in the spectrum. These ideas are supported by vibronic coupling calculations. The fact that the intensities of features corresponding to the two different vibronic symmetries are comparable is thus accidental.

The electronic and vibrational absorption spectra of the radical anion and cation of p-benzoquinone (PBQ) in an Ar matrix between 500 and 40000 cm−1 are presented and discussed in detail. Of particular interest is the radical cation, which shows very unusual spectroscopic features that can be understood in terms of vibronic coupling between the ground and a very low-lying excited state. The infrared spectrum of PBQ˙+ exhibits a very conspicuous and complicated pattern of features above 1900 cm−1 that is due to this electronic transition, and offers an unusually vivid demonstration of the effects of vibronic coupling in what would usually be a relatively simple region of the electromagnetic spectrum associated only with vibrational transitions. As expected, the intensities of most of the IR transitions leading to levels that couple the ground to the very low-lying first excited state of PBQ˙+ increase by large factors upon ionization, due to “intensity borrowing” from the D0 → D1 electronic transition. A notable exception is the antisymmetric CO stretching vibration, which contributes significantly to the vibronic coupling, but has nevertheless quite small intensity in the cation spectrum. This surprising feature is rationalized on the basis of a simple perturbation analysis.

The Ã2E″← 2A′2 absorption spectrum exhibits vibronically allowed transitions from the ground state of NO3 to upper state levels having a″1 and e′ vibronic symmetries. This paper explores the coupling mechanisms that lend intensities to these features. While transitions to e′ vibronic levels borrow intensity from the very strong 2E′← 2A′2 electronic transition, those to a″1 levels involve only negligible upper-state borrowing effects. Rather, it is the vibronic mixing of the ground vibronic level of NO3 with vibrational levels in the 2E′ electronic state that permit the a″1 levels to be seen in the spectrum. These ideas are supported by vibronic coupling calculations. The fact that the intensities of features corresponding to the two different vibronic symmetries are comparable is thus accidental.