Total ionization cross section of cyclic organic molecules.

Two independent methods, namely, Binary-encounter Bethe (BEB) and complex scattering potential-ionization contribution (CSP-ic) methods, are employed to calculate the total ionization cross section (Qion) for cyclic organic molecules from ionization threshold to 5 keV for which there is a paucity of data in the literature. The Qion calculated with the (BEB/ωB97X) combination is found to give good agreement with the experimental results, the CSP-ic method, and the Qion calculated from Irikura orbital energies. The Qion for most of the targets are calculated for the first time over such a wide energy range. Hence, to check the consistency and reliability of the present data, we have also computed the static polarizability for all the targets and the variation of maximum ionization cross section (Qion,max) with polarizability is studied. A linear relationship is observed between these quantities indicating the consistency and reliability of the present Qion data. The targets studied are important for industrial applications, radiation biology, and astrophysics.

Factors Affecting the Branching Ratio of Photodissociation: Thiophenol Studied through Quantum Wavepacket Dynamics.

The photodissociation dynamics of thiophenol (PhSH) excited to the 1(1) ππ* state was investigated by time-dependent quantum wavepacket propagation within two-dimensional (2D) space consisting of the S-H bond and -SH torsion. We systematically studied the dependence of the branching ratio (Ã/X(~)) between the two electronic states of the phenylthiyl radical (PhS(.) ) on several factors of the 2D potential energy surfaces (PESs). The effect of a reduced initial barrier to the first ππ*/πσ* conical intersection (CI) was found to be marginal, whereas the effects of a reduced torsional barrier of -SH on the excited ππ* state and the mitigated slope of the πσ* PES between the first (ππ*/πσ*) and the second (πσ*/S0 ) CIs were noticeable. The effect of the slope on the branching ratio has never been previously noticed. It was shown that the branching ratio can be sufficiently above unity without pre-excitation of the torsion mode of -SH, which has been assumed so far.

Ambient carbon dioxide capture by boron-rich boron nitride nanotube.

Carbon dioxides (CO(2)) emitted from large-scale coal-fired power stations or industrial manufacturing plants have to be properly captured to minimize environmental side effects. From results of ab initio calculations using plane waves [PAW-PBE] and localized atomic orbitals [ONIOM(wB97X-D/6-31G*:AM1)], we report strong CO(2) adsorption on boron antisite (B(N)) in boron-rich boron nitride nanotube (BNNT). We have identified two adsorption states: (1) A linear CO(2) molecule is physically adsorbed on the B(N), showing electron donation from the CO(2) lone-pair states to the B(N) double-acceptor state, and (2) the physisorbed CO(2) undergoes a carboxylate-like structural distortion and C═O π-bond breaking due to electron back-donation from B(N) to CO(2). The CO(2) chemisorption energy on B(N) is almost independent of tube diameter and, more importantly, higher than the standard free energy of gaseous CO(2) at room temperature. This implies that boron-rich BNNT could capture CO(2) effectively at ambient conditions.

Photodissociation dynamics of thiophenol-d1: the nature of excited electronic states along the S-D bond dissociation coordinate.

The S-D bond dissociation dynamics of thiophenol-d1 (C6H5SD) pumped at 266, 243, and 224 nm are examined using the velocity map ion imaging technique. At both 266 and 243 nm, distinct peaks associated with X and A states of the phenylthiyl radical (C6H5S*) are observed in the D+ image at high and low kinetic energy regions, respectively. The partitioning of the available energy into the vibrational energy of the phenylthiyl radical is found to be enhanced much more strongly at 266 nm compared to that at 243 nm. This indicates that the pipi* electronic excitation at 266 nm is accompanied by significant vibrational excitation. Given the relatively large anisotropy parameter of -0.6, the S-D dissociation at 266 nm is prompt and should involve the efficient coupling to the upper-lying n(pi)sigma* repulsive potential energy surface. The optical excitation of thiophenol at 224 nm is tentatively assigned to the pisigma* transition, which leads to the fast dissociation on the repulsive potential energy surface along the S-D coordinate. The nature of the electronic transitions associated with UV absorption bands is investigated with high-level ab initio calculations. Excitations to different electronic states of thiophenol result in unique branching ratios and vibrational excitations for the fragment of the phenylthiyl radical in the two lowest electronic states.

Structure of pyridazine in the S1 state: experiment and theory.

The molecular structure of pyridazine in the first electronically excited state (S(1)) is deduced from the combined use of resonance-enhanced two-photon ionization and mass-analyzed threshold ionization spectroscopic methods. The equation-of-motion coupled-cluster single and double (EOM-CCSD) calculation gives the distorted planar geometry for the most stable structure of the S(1) pyridazine. The symmetry constraint of C(2v) is relaxed to that of C(s), and consequently many in-plane vibrational modes are found to be optically active in both S(1)-S(0) and D(0)-S(1) excitation spectra, being appropriately assigned from the comparison of their frequencies with ab initio values. This indicates that the S(1)-S(0) excitation is partially localized, and provides an alternative explanation for the long-standing spectroscopic puzzle in S(1) pyridazine.