Search

Discusses the multichannel quantum defect theory simulations of excitation spectra to autoionizing high-n (n=13-150) Rydberg states for argon, hydrogen and nitrogen. Effects or rotational channel couplings in H and N; Preservation of window resonance in H in the presence of a strong field; Non-zero-quantum defects and their impact on Rydberg states.

Mass analyzed threshold ionization (MATI) spectra of NH3 are recorded using two-color (2+1')multiphoton excitation via the B~ and C~' states using multichannel quantum defect theory, where new vibrational bands are reported for intermediate levels. The achievement of multichannel defect theory by using a handful of quantum defect parameters suggest that ZEKE and MATI spectroscopies can be regarded as fully interpretable techniques.

The detection of ions or electrons from the surface ionisation of molecular H2and atomic H Rydberg states incident at doped Si surfaces is investigated experimentally to analyse the effect of the dopant charge distribution on the surface-ionisation processes. In both experimental studies, the molecular H2and atomic H Rydberg states are generated via two-colour vacuum ultraviolet--ultraviolet (VUV–UV) resonant excitation. For H2, various Stark states of theN+= 2,n= 17 manifold are populated in the presence of an electric field. The variation of the observed surface-ionisation signal with surface dopant concentration and type, shows similar characteristics for all the Stark states. A comparison is made between these ion-detected surface-ionisation profiles and those obtained via electron detection. Different trends as a function of dopant concentration and type are observed for the two cases, explained by the greater effect of surface charges on the post-ionisation ion trajectory compared to the electron trajectory. For the atomic-H Rydberg states with principal quantum numberpopulated in the absence of a Stark field, the observed behaviour is similar to the interaction of molecular H2Rydberg states at the same surfaces, and these measurements confirm that the observed effects are attributable to the nature of the target surface rather than the specific atomic or molecular Rydberg species. [ABSTRACT FROM PUBLISHER]

Jet-cooled spectra of14NH3and15NH3in natural abundance were recorded using cavity ring-down (CRDS, 6584–6670 cm−1) and cavity enhanced absorption (CEAS, 6530–6700 cm−1) spectroscopy. Line broadening effects in the CRDS spectrum allowed lines withJ″-values between 0 and 3 to be identified. Intensity ratios in14NH3between the jet-cooled CRDS and literature room-temperature data from Sunget al. (J. Quant. Spectrosc. Radiat. Transfer, 113 (2012), 1066) further assisted the line assignments. Ground state combination differences were extensively used to support the assignments, providing reliable values forJ,Kand inversion symmetry of the ground state vibrational levels. CEAS data helped in this respect for the lowestJlines, some of which are saturated in the CRDS spectrum. Further information on a/s doublets arose from the observed spectral structures. Thirty-two transitions of14NH3were assigned in this way and a limited but significant number (19) of changes in the assignments results, compared to Sunget al. or to Caccianiet al. (J. Quant. Spectrosc. Radiat. Transfer, 113 (2012), 1084). Sixteen known and 25 new low-Jtransitions were identified for15NH3in the CRDS spectrum but the much scarcer literature information did not allow for any more refined assignment. The present line position measurements improve on literature values published for15NH3and on some line positions for14NH3. [ABSTRACT FROM PUBLISHER]

An extension of the model of Merkt and Zare [J. Chem. Phys. 101, 3495 (1994)] is presented to describe the effects of static inhomogeneous electric fields, which arise experimentally from combinations of applied (or stray) homogeneous fields and the presence of charged particles, on Rydberg states of atoms and molecules. The effect of an arbitrary number of charged particles is included and the effects of nonzero quantum defects are investigated. A quantization axis rotation procedure is defined, allowing clear distinction between homogeneous and inhomogeneous field effects. Calculations are reported of the time-dependent decay of a coherent population of eigenstates for n=20, 33, and 50, involving diagonalization of the full n[sup 2]xn[sup 2] matrix. Calculations are also carried out for n=100 by pre-diagonalization of the full homogeneous field perturbation followed by a restricted basis set diagonalization for the inhomogeneous part of the perturbation. The inclusion of nonzero quantum defects has a substantial impact on the m[sub l] mixing, confining significant mixing to a narrow range of radial and angular positions of the ion. An applied homogeneous field of order the Inglis-Teller field is required in combination with the field due to the ions. The dynamics are very different according to whether np or nf series carry the transition probability. For np-state population, the maximum stabilization is achieved at ion-Rydberg distances of around 5n[sup 2]a[sub 0], with the ion almost perpendicular to the applied homogeneous field. For an initial nf population the ion perturbation may have a destabilizing effect at sufficiently small homogeneous field (<=0.1F[sub IT]). Significant effects of laser polarization on the stability are reported. Calculations for a realistic pseudo-random distribution of ions and Rydbergs suggest that m[sub l] mixing by ions will never reach the complete mixing limit, but that at least an order of magnitude stabilization is a... [ABSTRACT FROM AUTHOR]