Dipole-bound anions

Bailey C G, Dessent C E FI, Johnson M A and Bowen K FI 1996 Vibronic effects in the photon energy-dependent photoelectron spectra of the CFIjCN dipole-bound anion J. Chem. Phys. 104 6976-83... 

Dipole-bound anions (5a, 4f) in which the extra electron is attracted primarily by the dipole force field of the polar molecule and for which rotation-to-electronic coupling is most important in inducing electron ejection. 

Fig. 3 Relative dipole-bound anion formation rates in RET collisions between Rydberg Xe(nf) atoms with (a) adenine (circles) or imidazole (squares) molecules and (b) adenine-imidazole complex produced in a supersonic beam. Experimental data are fitted to curvecrossing model calculations which lead to the experimental determination of EAdS values, equal to 11 meV for adenine, 23 meV for imidazole and 54 meV for adenine-imidazole complex (reproduced by permission of the American Chemical Society).

Fig. 14 Relative dipole bound anion formation rates in RET collisions between Rydberg Xe(nf) atoms and a supersonic beam of (R)-l-phenylethanol (E/ ) with 2-pyrrolidinmethanols (PRand P5).

Skurski, P., Gutowski, M., Simons, J. How to choose a one-electron basis set to reliably describe a dipole-bound anion. Int. J. Quantum Chem. 2000, 80, 1024-38. 

Solvation of DNA bases/base pairs is of fundamental importance to biological processes as they take place in aqueous media. The effect of hydration on neutral bases or base pairs has been addressed using quantum chemical methods [106-112] as well as molecular dynamics (MD) simulations [113, 114], It is known that unlike the gas phase, dipole bound anions do not exist in condensed environments because such diffuse states are destabilized in the aqueous phase [115]. The drastic change in the nature of excess electron binding in the presence of water molecules with uracil has been observed experimentally by Bowen and co-workers [95b] using negative electron photoelectron spectroscopy (PES). They observed that even with a single water molecule the dipole bound state of uracil anion in gas phase... 

Gutowski M, Skurski P, Simons J (2000). Dipole-bound anions of glycine based on the zwitterion and neutral structures. J Am Chem Soc 122 10159-10162. 

Haranczyk M, Gutowski M (2005). Valence and dipole-bound anions of the most stable tautomers of guanine. J Am Chem Soc 127 699-706. 

Jalbout A, Adamowicz L (2001). Dipole-bound anions of adenine-water clusters. Ab initio study. 

For cytosine two DBEA are reported 0.230 eV and 0.085 eV. Interestingly, the dipole bound states are observed in the PES of the dihydrates due to two-photon absorption. The first photon removes the waters and then a second photon detaches the electron from the dipole bound state. These spectra for cytosine are shown in Figure 12.3. The spectrum of the bare cytosine is shown in the inset offset by 1.5 eV. The peak at 0.230 eV is assigned to the dipole bound anion of keto-cytosine, whereas the peak at 0.085 eV is assigned to the enol form of the anion. The dipole moment of the enol form is about 4 Debye, while that for the keto form is about 6.5 Debye. The two peak intensities are quite different in the spectrum for the monomer. In the spectrum for the dihydrate the intensities are about the same. The double-photon process explains this difference. The absorption of the initial photon by the dihydrate leaves equal concentrations of two forms that are then photode-tached. In the spectrum of the bare anion the distribution reflects the equilibrium concentrations. The extra structure in the spectrum of the dihydrate can be attributed to excited states of the anion and offers a different interpretation of the onset. 

Since the dipole bound anions are formed by double-photon absorption, the valence states could also be formed, in which case the onsets and initial peaks results from the photodetachment of the isolated ground-state or excited-state anions. These can be a measure of the Ea. The onsets that are lower than the... 

In Figure 12.15 the planar local minimum form of G(—) is shown with a three-dimensional spin density plot. The spin density is localized on the hydrogen bonding sites and is similar to a dipole bound anion. Figure 12.16 presents a similar plot for the global minimum form of G(—). The NH2 group is twisted out of the plane,... 

Electron structure of a dipole-bound anion confined in a... 

Electron structure of a dipole-bound anion confined in a spherical box. Addendum to Electron structure of a dipole-bound anion in a spherical box The case of a finite dipole... 

Examples of Dipole-Bound Anions and Likely Examples of... 

Figure 6 also summarizes the measured binding energies for dipole states versus the molecular dipole moment which adds to the data reported in the seminal papers by Desfrancois et al. The Schermarm group has provided a comprehensive review of ground-state dipole-bound anions studied... 

From a historical perspective, the first unambiguous observation of dipole states came from the group of Kit Bowen (Johns Hopkins) in 1990, who studied the important water dimer dipole anion. The Bowen group has also studied ground state dipole-bound anions produced by electron attachment under high-pressure nozzle-jet expansion condition. They have also used photodetachment photoelectron spectroscopy to determine electron affinities for a number of the molecules shown in Figure 4. 

The group of Mark Johnson (Yale) has produced dipole-bound anions from photodissociation of the iodine atom/acetone and iodine atom/ acetonitrile (CH3CN) neutral clusters. Dipole-bound anions have been... 

Dipole-bound anions are characterized both by their small electron affinities and diffuse nature. Laser photodetachment of dipole-bound anions leave the neutral molecule in the same (or approximately so) vibrational state as that of the anion. The diffuse nature of the dipole-bound anions... 

V. EXAMPLES OF DIPOLE-BOUND ANIONS AND LIKELY EXAMPLES OF QUADRUPOLE-BOUND ANIONS... 

Figure 79. Potential energy surfaces for CH3NO2 and (CH3N02) anions. The surface representing the dipole-bound anion lies ( 0.012 eV) below that of CH3NO2 and the valence-bound anion lies 0.26 eV below the neutral.

Nitrobenzene, j zra-dinitrobenzene (/zDNB) and me/a-dinitrobenzene (mDNB) anions have both diffuse multipole-bound and valence-anion states. For nitrobenzene and m-dinitrobenzene, the diffuse states are believed to correspond to dipole-bound anions whereas />DNB anions are considered to be primarily described as quadrupole-bound states. Nitrobenzene anions (NB ) in both valence and dipole-bound states were examined using RET spectroscopy. R<3ra-dinitrobenzene (zero dipole moment and a large quadrupole moment) and me <3-dinitrobenzene (large dipole moment and a small quadrupole moment) were also studied using R T 106 20 shows the /-dependence of the reaction rates for... 

Readers who wish to learn more about how molecular EAs (and to a lesser extent, IPs) have been studied theoretically are directed to this author s web site http //simons.hec. utah.edu as well as to a series [38] of his reviews and chapters. The species that this group have examined include dipole-bound anions, zwitterion ions, conventional valence anions, multiply charged anions as well as a wide variety of metastable anions. 

---