Spin-orbit relaxation of Cl(P1∕22) and F(P1∕22) in a gas of H2

Picosecond to Nanosecond Manipulation of Excited-State Lifetimes in Complexes with an FeII to TiIV Metal-to-Metal Charge Transfer: The Role of Ferrocene Centered Excited States

Time-resolved transient absorption spectroscopy and computational analysis of D-π-A complexes comprising Fe^II donors and Ti^IV acceptors with the general formula ^RCp₂Ti(C₂Fc)₂ (where ^RCp = Cp*, Cp, and ^MeOOCCp) and ^TMSCp₂Ti(C₂Fc)(C₂R) (where R = Ph or CF₃) are reported. The transient absorption spectra are consistent with an Fe^III/Ti^III metal-to-metal charge-transfer (MMCT) excited state for all complexes. Thus, excited-state decay is assigned to back-electron transfer (BET), the lifetime of which ranges from 18.8 to 41 ps. Though spectroscopic analysis suggests BET should fall into the Marcus inverted regime, the observed kinetics are not consistent with this assertion. TDDFT calculations reveal that the singlet metal-to-metal charge-transfer (¹MMCT) excited state for the Fe^II/Ti^IV complexes is not purely MMCT in nature but is contaminated with the higher-energy ¹Fc (d-d) state. For the diferrocenyl complexes, ^RCp₂Ti(C₂Fc)₂, the ratio of MMCT to Fc centered character ranges from 57:43 for the Cp* complex to 85:15 for the ^MeOOCCp complex. For the diferrocenyl and monoferrocenyl complexes investigated herein, the excited-state lifetimes decrease with increased ¹Fc character. The effect of Cu^I coordination was also analyzed by time-resolved transient absorption spectroscopy and reveals the elongation of the excited-state lifetime by 3 orders of magnitude to 63 ns. The transient spectra and TDDFT analysis suggest that the long-lived excited state in Cp₂Ti(C₂Fc)₂·CuX (where X is Cl or Br) is a triplet iron species with an electron arrangement of Ti^IV-³Fe^II-Cu^I.

Spin-orbit quenching of Cl(2P(1∕2)) by H2

We report fully-quantum, time-independent, scattering calculations for the spin-orbit quenching of Cl((2)P(1∕2)) by H(2) molecules at low and moderate temperature. Our calculations take into account chemical reaction channels. Cross sections are calculated for total energies up to 5000 cm(-1) which are used to determine, by thermal averaging, state-to-state rate coefficients at temperatures ranging from 50 to 500 K. Spin-orbit relaxation of chlorine is dominated by collisions with H(2) in the rotationally excited states j = 2 and j = 3. In the former case the near-resonant energy transfer is the primary relaxation mechanism. The inclusion of the reactive channel could lead differences compared to pure inelastic calculations. Good agreement is obtained with experimental relaxation measurements at room temperature.

Space-time contours to treat intense field-dressed molecular states

In this article we consider a molecular system exposed to an intense short-pulsed external field. It is a continuation of a previous publication [A. K. Paul, S. Adhikari, D. Mukhopadhyay et al., J. Phys. Chem. A 113, 7331 (2009)] in which a theory is presented that treats quantum effects due to nonclassical photon states (known also as Fock states). Since these states became recently a subject of intense experimental efforts we thought that they can be treated properly within the existing quantum formulation of dynamical processes. This was achieved by incorporating them in the Born-Oppenheimer (BO) treatment with time-dependent coefficients. The extension of the BO treatment to include the Fock states results in a formidable enhancement in numerical efforts expressed, in particular, in a significant increase in CPU time. In the present article we discuss an approach that yields an efficient and reliable approximation with only negligible losses in accuracy. The approximation is tested in detail for the dissociation process of H(2) (+) as caused by a laser field.

Intralines of quasi-conical intersections on torsion planes: methylamine as a case study

Recently we reported on a novel feature associated with the intersection of the two lowest states (1)A' and (1)A'' of the methylamine (J. Chem. Phys. 2008, 128, 244302). We established the existence of a finite (closed) line of conical intersections (ci), namely, a finite seam, located in the HC-NHH symmetry plane, a line that is formed by moving a single hydrogen on that plane while locking the positions of the (six) other atoms. In the present article, this study is extended to the corresponding torsion planes formed by rotating the methyl group around the CN axis. The torsion planes, in contrast with the HC-NHH symmetry plane, do not satisfy the symmetry feature that enables the seam just mentioned. Nevertheless, the calculated nonadiabatic coupling terms (NACTs) resemble features similar to those encountered in the HC-NHH symmetry plane. Following a tedious numerical study supported by a theoretical model (Section III), it was verified that these NACTs may become similar to those on the symmetry plane, sometimes even to the level of almost no distinction, but lack one basic feature; namely, they are not singular and therefore do not form topological effects.