The spectroscopy of high Rydberg states of ammonia (original) (raw)
Related papers
Chemical Physics Letters, 1996
Progression of bands associated with the v 2 (bending) vibrational mode of the F.'l,(1 (4pa'~ ~ 3a l) Rydberg states of both NH 3 and ND 3 have been observed as two-photon resonances in the multiphoton ionisation spectrum of these two isotopomers at excitation wavelengths in the range 275-248 nm. Band contour analysis yields excited state spectroscopic parameters and some insight into the predissociation behaviour of these levels, all of which show many parallels with previous knowledge concerning the C'I.~ 1 Rydberg state of ammonia (arising from the corresponding 3pa'~ *-3a I orbital promotion).
Chemical Physics, 1991
A series of ab initio CI calculations is reported for the electronic spectrum of ammonia. The generalized oscillator strength for the A-X n+3s Rydberg transition is computed as a function of the square of the momentum transfer vector in electron impact studies and the results are found to be in good agreement with the corresponding measured data. Vertical and adiabatic transition energies are also reported for a series of low-energy Rydberg transitions involving 3p, 3d, 4s and 4p upper orbitals and these results are also found to compare well with the corresponding experimental findings. Optical Svalues for the latter transitions have also been computed.
High-resolution infrared spectroscopy of ammonia: A survey of theory and analyses of spectra
Journal of Quantitative Spectroscopy and Radiative Transfer, 1992
Almtmet-The vibration-rotation spectrum of ammonia is important for astrophysical and meteorological applications. We present here an outline of the theory of vibration-inversionrotation Hamiltonians for pyramidal XY, molecules. Consequences of large amplitude inversions on molecular symmetry and dynamics are discussed. Special attention is paid to the vibration-rotation Coriolis interactions between energy levels of the v&ending and V.-degenerate vibrational modes, as well as various l-type and centrifugal distortion operators. Anomalous intensities resulting from strong vibration-rotation interactions are also discussed.
Near infrared transitions between Rydberg states of nitric oxide
Journal of Molecular Spectroscopy, 1981
Several near infrared transitions between highly excited Rydberg (R) states of nitric oxide have been recorded at high resolution (0.15 cm-') with a SISAM interferometer. The spectra all show a simple rotational structure, characteristic of R-R transitions. A full analysis has been performed of the previously unobserved 4f (u = 0) + F*A(u = 0) band at 1.71 pm. The band shows a peculiar structure, characteristic of Hund's Case (d) behaviour for one of the states. The relative branch intensities are calculated from first principles, and the agreement with the observed spectrum is excellent. This work shows the potential of interferometers for studying excited electronic states of simple molecules at high resolution.
Spectroscopic Observation and Characterization of H + H − Heavy Rydberg States †
The Journal of Physical Chemistry A, 2009
A series of discrete resonances was observed in the spectrum of H 2 , which can be unambiguously assigned to bound quantum states in the 1/R Coulombic potential of the H + Hion-pair system. Two-step laser excitation was performed, using tunable extreme ultraviolet radiation at λ) 94-96 nm in the first step, and tunable ultraviolet radiation in the range λ) 310-350 nm in the second step. The resonances, detected via H + and H 2 + ions produced in the decay process, follow a sequence of principal quantum numbers (n) 140-230) associated with a Rydberg formula in which the Rydberg constant is mass scaled. The series converges upon the ionic H + Hdissociation threshold. This limit can be calculated without further assumptions from known ionization and dissociation energies in the hydrogen system and the electronegativity of the hydrogen atom. A possible excitation mechanism is discussed in terms of a complex resonance. Detailed measurements are performed to unravel and quantify the decay of the heavy Rydberg states into molecular H 2 + ions, as well as into atomic fragments, both H(n) 2) and H(n) 3). Lifetimes are found to scale as n 3 .
Preparation and characterization of long-lived molecular Rydberg states: Application to HD
The Journal of Chemical Physics, 1996
The decay dynamics by predissociation and rotational autoionization of high Rydberg states of HD close to the first few rotational levels of the ground vibronic state of the HD ϩ cation have been studied by delayed pulsed field ionization following resonant ͑1ϩ1Ј͒ two-photon absorption via the B state. Although predissociation and autoionization both contribute to the rapid decay of Rydberg states with principal quantum number nӶ100, the highest Rydberg states ͑nϾ100͒ are stable for more than 20 s. In contrast to H 2 , channels associated with an HD ϩ ͑v ϩ ϭ0, N ϩ ϭeven͒ ion core are coupled to channels associated with an HD ϩ ͑v ϩ ϭ0, N ϩ ϭodd͒ ion core. We demonstrate that complex resonances that arise from rotational channel interactions between low ͑nϳ25͒ Rydberg states characterized by a core with rotational angular momentum quantum number N ϩ ϩ2 and the pseudocontinuum of very high Rydberg states characterized by an N ϩ core can be used with high efficiency to produce long-lived high Rydberg states. An investigation of the pulsed field ionization characteristics of these complex resonances enables us to measure the branching between diabatic and adiabatic field ionization and to determine the optimal conditions required to extend the method of H-photofragment Rydberg translational spectroscopy pioneered by Schnieder et al. ͓J. Chem. Phys. 92, 7027 ͑1990͔͒ to molecular species.
Complete Assignment of the Infrared Spectrum of the Gas-Phase Protonated Ammonia Dimer
The infrared (IR) spectrum of the ammoniated ammonium dimer is more complex than those of the larger protonated ammonia clusters due to close-lying fundamental and combination bands and possible Fermi resonances (FR). To date, the only theoretical analysis involved partial dimensionality quantum nuclear dynamic simulations, assuming a symmetric structure (D3d) with the proton midway between the two nitrogen atoms. Here we report an extensive study of the less symmetric (C3v) dimer, utilizing both second order vibrational perturbation theory (VPT2) and ab initio molecular dynamics (AIMD), from which we calculated the Fourier transform (FT) of the dipole-moment autocorrelation function (DACF). The resultant IR spectrum was assigned using FTed velocity autocorrelation functions (VACFs) of several interatomic distances and angles. At 50 K, we have been able to assign all 21 AIMD fundamentals, in reasonable agreement with MP2-based VPT2, about 30 AIMD combination bands, and a difference band. The combinations involve a wag or the NN stretch as one of the components, and appear to follow symmetry selection rules. On this basis, we suggest possible assignments of the experimental spectrum. The VACF-analysis revealed two possible FR bands, one of which is the strongest peak in the computed spectrum. Raising the temperature to 180 K eliminated the " proton transfer mode " (PTM) fundamental, and reduced the number of observed combination bands and FRs. With increasing temperature, fundamentals red-shift, and the doubly degenerate wags exhibit larger anharmonic splittings in their VACF bending spectra. We have repeated the analysis for the H3ND+NH3 isotopologue, finding that it has a simplified spectrum, with all the strong peaks being fundamentals. Experimental study of this isotopologue may thus provide a good starting point for disentangling the N2H7+ spectrum.
The ammonia dimer: new infrared-far infrared double resonance results
Chem Phys, 1995
From the results of an infrared-far infrared double resonance experiment on (NH 3) 2 complexes in a supersonic slit nozzle expansion, it was possible to characterize the tunneling dynamics, occurring within the ammonia dimer (Havenith et al., Chem. Phys. Letters 193 (1992) 261). In the current paper we present additional infrared-far infrared double resonance spectra. These confirm the former analysis and give a state specific explanation of the overall infrared spectrum of (NH 3) 2 as measured by Snels et al. (Chem. Phys. 115 (1987) 79). The interchange motion is shown to be quenched from 20 cm -1 in the ground state to less than 1 cm -1 in the infrared excited state. This confirms the assumption of Olthof et al. (J. Mol. Struct. THEOCHEM 307 (1994) 201) that the barrier for interchange tunneling is very small in (NH 3) 2.
The E2Σ+ → C2Π Transition of NO and Term Values for the A, D, E, and C Lowest Rydberg Levels
Journal of Molecular Spectroscopy, 2000
The E 2 ⌺ ϩ 3 C 2 ⌸ Rydberg-Rydberg transition of 14 N 16 O near 8492 cm Ϫ1 has been studied by Fourier transform spectrometry in the emission from a dc excited supersonic jet expansion and from a dc discharge under equilibrium conditions. The same transition has also been observed in laser-induced stimulated emission. Line wavenumbers of the 0 -0, 1-1, and 2-2 bands, together with data for previously published near-infrared transitions, have been reduced to consistent sets of rovibronic term values for v ϭ 0, 1, and 2 of the A 2 ⌺ ϩ , D 2 ⌺ ϩ , E 2 ⌺ ϩ , and C 2 ⌸ states which frequently serve as intermediates in the multiphoton excitation of higher Rydberg levels of NO.
Rovibrational intensities in the ν4 band of ammonia
Journal of Molecular Structure, 1999
Absolute line intensities of sixteen rovibrational transitions in the n 4 band of 14 NH 3 were measured around 1800 cm Ϫ1 using a tunable diode laser spectrometer with a sweep modulation of the laser frequency. Individual laser scans over the line region were recorded to disk storage separately and the spectrum accumulation was performed off-line using a computer to reduce a significant line broadening because of a lower accuracy of the hardware on-line accumulation.