Joseph B. Kim

Autodetachment spectroscopy and dynamics of vibrationally excited dipole-bound states of H2CCC−

Direct observation of the rotational fine structure levels of a vibrationally excited negative ion dipole‐bound state (DBS) is reported. Autodetachment resonances of H2CCC− were observed for the 2A1−2B1 transition in one quanta of ν6, ν4, and ν2 and two quanta of ν6 vibrational modes of the DBS. Rotational assignments for both the electronic ground state and the DBS were performed. Strong type (a) Coriolis coupling between ν6 and ν9 in both the electronic ground and excited states was observed, and coupling constants were determined. QCISD ab initio calculations were performed for the ground state, the negative ion, and the neutral state of H2CCC. The calculations on the neutral agree well with measured vibrational frequencies of the dipole‐bound state. The autodetachment resonances contain information about the detachment dynamics via the observed linewidths, showing, e.g., that motions along the dipole moment axis significantly enhance autodetachment, indicating that the DBS is unstable with respect to ...

Autodetachment spectroscopy and dynamics of dipole bound states of negative ions: 2A1–2B1 transitions of H2CCC−

The H2CCC− ion is studied by autodetachment spectroscopy in a coaxial laser‐ion beam spectrometer. Sharp resonances at photon energies near the photodetachment threshold energy are ascribed to a 2A1←2B1 transition followed by autodetachment of the dipole‐bound state (DBS). Some 2500 rotational transitions are assigned and the band origin is determined to be 14 284.420(5) cm−1. The observation of individual rotational lines allowed determination of the rotational spectroscopic constants as A=9.651 53(4) cm−1 and (B+C)/2=0.346 461(3) cm−1 for the DBS as well as the spin‐rotation coupling constant eaa=2.17(6)×10−3 cm−1. Based on an electron affinity of 14 469±64 cm−1, the binding energy of the electron in the DBS is 170±50 cm−1. Anomalous rotational line positions are found in the vicinity of Ka=7–10 in the DBS and have been attributed to the centrifugal distortion couplings caused by mixing with the CCC out‐of‐plane bending mode (ν6) and the CCC in‐plane bending mode (ν9). The linewidths provide information...

Photoelectron spectroscopy of OH−(N2O)n=1–5

The 351 nm photoelectron spectra of OH−(N2O)n, n=1–5, are reported. Each spectrum is composed of a single broad feature that shifts toward higher electron binding energy as the number of solvent molecules increases. Analysis of OH−(N2O) spectra at ion temperatures of 200 and 300 K shows that there is significant intensity in the 000 transition, and that transitions to the dissociative region of the OH+N2O potential energy surface are also accessed. The electron affinity of OH(N2O) is estimated to be 2.14±0.02 eV, from which the OH–N2O bond dissociation energy is calculated as 0.39 eV. The photoelectron spectra of OH−(N2O)n>1 are accurately modeled as the convolution of the OH−(N2O) spectrum with the OH−(N2O)n−1. The anion vertical detachment energies and the adiabatic electron affinities for OH(N2O)n=2–5 are obtained and the thresholds for stepwise dissociation of N2O are located, indicating that photodetachment accesses multiple dissociation channels.

Negative ion photoelectron spectroscopy of OH−(NH3)

The 351 nm photoelectron spectra of OH−(NH3)n n=1,2 and the deuterated analogs exhibit two broad peaks. Ab initio calculations of the anion and neutral potential-energy surfaces have been carried out using an MP2 (second-order Mo/ller–Plesset)/6-31++G** basis set. The geometries, frequencies, and energetics from these calculations aid in the interpretation of the experimental results. An estimate of the OH(NH3) electron affinity is 2.35±0.07 eV based on experimental and theoretical results. Calculations of the anion vibrational wave functions indicate that following electron photodetachment, the neutral potential-energy surface is accessed from the reactant entrance channel through the transition state region.

The identification of the Ca 3d4f autoionizing levels by the application of multiphoton polarization selection rules

We have used angular momentum selection rules to identify the J-levels of the Ca 3d4f autoionizing states. These levels were observed in one- plus two-photon resonance excitation directly to the autoionizing state using two different lasers. By choosing the appropriate combination of polarizations for the two lasers, we were able to provide positive identification for all of the J=1,2 and 3 levels observed. Our assignments extend those reported in the literature to the J=2 levels.