J.P. Sprengers

Extreme ultraviolet laser excitation of isotopic molecular nitrogen: The dipole-allowed spectrum of 15N2 and 14N15N

The work was supported by the European Community, under the Access to Research Infrastructures initiative of the Improving Human Potential Program, Contract No. HPRI-CT-1999-00064. K.G.H.B. was supported by the Scientific Visits to Europe Program of the Australian Academy of Science.

Isotopic variation of experimental lifetimes for the lowest (1)Pi(u) states of N-2

Lifetimes of several (1)Pi(u) states of the three natural isotopomers of molecular nitrogen, (14)N(2), (14)N(15)N, and (15)N(2), are determined via linewidth measurements in the frequency domain. Extreme ultraviolet (XUV)+UV two-photon ionization spectra of the b (1)Pi(u)(v=0-1,5-7) and c(3) (1)Pi(u)(v=0) states of (14)N(2), b (1)Pi(u)(v=0-1,5-6) and c(3) (1)Pi(u)(v=0) states of (14)N(15)N, and b (1)Pi(u)(v=0-7), c(3) (1)Pi(u)(v=0), and o (1)Pi(u)(v=0) states of (15)N(2) are recorded at ultrahigh resolution, using a narrow band tunable XUV-laser source. Lifetimes are derived from the linewidths of single rotationally resolved spectral lines after deconvolution of the instrument function. The observed lifetimes depend on the vibrational quantum number and are found to be strongly isotope dependent.

Lifetime and predissociation yield of N-14(2) b (1)Pi(u)(v=1)

The lifetime of the b (1)Pi(u)(v=1) state in N-14(2) has been determined experimentally using a laser-based pump-probe scheme and an exceptionally long lifetime of 2.61 ns was found. Semiempirical close-coupling calculations of the radiative lifetime, which include Rydberg-valence interactions in the singlet manifold, are consistent with this large value, giving a value of 3.61 ns and suggesting a predissociation yield of similar to28% for this level of the b state

Lifetime and predissociation yield of N-14(2) b (1)Pi(u)(v=1) revisited: Effects of rotation

This work was supported by Australian Research Council Discovery Program Grant No. DP0558962 and the European Community, through the Access to Research Infrastructures action of the Improving Human Potential Program, Contract No. HPRI-CT-1999-00041.

Vibrationally excited state spectroscopy of radicals in a supersonic plasma

Abstract A plasma source based on a multilayer discharge geometry in combination with a time-of-flight REMPI experiment is used to study rotationally cold spectra of highly excited vibrational states of mass selected radicals. The rovibrational state distributions upon discharge excitation are characterised for the example of NO for ground state vibrational levels up to v″=18. Whereas rotational temperatures are lower than 50 K, a vibrational temperature of Tvib=6700±700 K is found.

Structure and predissociation of the 3p sigma D-u (3)Sigma(+)(u) Rydberg state of N2: First extreme-ultraviolet and new near-infrared observations, with coupled-channels analysis

The 3psigma(u)D (3)Sigma(u) (+) Rydberg state of N(2) is studied experimentally using two high-resolution spectroscopic techniques. First, the forbidden D (3)Sigma(u) (+)-X (1)Sigma(g) (+) transition is observed for the first time via the (0,0) band of (14)N(2) and the (1,0) band of (15)N(2), using 1 extreme-ultraviolet +1 ultraviolet two-photon-ionization laser spectroscopy. Second, the Rydberg-Rydberg transition D (3)Sigma(u) (+)-E (3)Sigma(g) (+) is studied using near-infrared diode-laser photoabsorption spectroscopy, thus extending the previous measurements of Kanamori et al. [J. Chem. Phys. 95, 80 (1991)], to higher transition energies, and thereby revealing the (2,2) and (3,3) bands. The combined results show that the D(v=0-3) levels exhibit rapidly increasing rotational predissociation as v increases, spanning nearly four orders of magnitude. The D-state level structure and rotational predissociation signature are explained by means of a coupled-channels model which considers the electrostatically coupled (3)Pi(u) Rydberg-valence manifold, together with a pure-precession L-uncoupling rotational interaction between the 3psigma(u)D (3)Sigma(u) (+) and 3ppi(u)G (3)Pi(u) Rydberg p-complex components.

Optical observation of the 3sσgFΠu3 Rydberg state of N2

Using ultrahigh-resolution 1XUV+1UV two-photon ionization laser spectroscopy, the FΠu3←XΣg+1(0,0) transition of N2 has been optically observed for the first time, and the 3sσgFΠu3(υ=0) Rydberg level fully characterized with rotational resolution. The experimental spectroscopic parameters and predissociation level widths suggest strong interactions between the F state and the 3pπuGΠu3 Rydberg and C′Πu3 valence states, analogous to those well known in the case of the isoconfigurational Πu1 states.

Quantum-interference effects in the o(1)Pi(u)(v=1)similar to b(1)Pi(u)(v=9) Rydberg-valence complex of molecular nitrogen

Two distinct high-resolution experimental techniques, 1 UV laser-based ionization spectroscopy and synchrotron-based XUV photoabsorption spectroscopy, have been used to study the o Rydberg–valence complex of 14N2, providing new and detailed information on the perturbed rotational structures, oscillator strengths, and predissociation linewidths. Ionization spectra probing the b state of 14N2, which crosses o1Πu(v=1) between J = 24 and J = 25, and the o1Πu(v=1), b,1Πu(v=9), and b states of 14N15N, have also been recorded. In the case of 14N2, rotational and deperturbation analyses correct previous misassignments for the low-J levels of o(v=1) and b(v=9). In addition, a two-level quantum-mechanical interference effect has been found between the o–X(1, 0) and b–X(9, 0) transition amplitudes which is totally destructive for the lower-energy levels just above the level crossing, making it impossible to observe transitions to b(v=9,J=6). A similar interference effect is found to affect the o(v=1) and b(v=9) predissociation linewidths, but, in this case, a small non-interfering component of the b(v=9) linewidth is indicated, attributed to an additional spin–orbit predissociation by the repulsive state.

High precision frequency calibration of N I lines in the XUV domain

With the use of a narrowband and tunable extreme ultraviolet laser source transition frequencies in the spectrum of neutral atomic nitrogen were measured for transitions originating from the (2p3)4S3/2 ground state to 12 levels in the 2p23d and 2p24s configurations in the wavelength range 95.1–96.5 nm. The present laboratory calibrations, performed at an absolute accuracy of 0.005 cm−1 or 5 × 10−8, should be useful for comparison with nitrogen absorption features observed in quasars for assessment of possible temporal variation of the fine structure constant. Simultaneous recordings of spectra for both 14N and 15N yield accurate values for transition isotope shifts, which reveal large specific-mass shifts almost to the extent of cancelling the isotope shifts.

Optical observation of the 3s sigma F-g (3)Pi(u) Rydberg state of N-2

Using ultrahigh-resolution 1XUV+1UV two-photon ionization laser spectroscopy, the FΠu3←XΣg+1(0,0) transition of N2 has been optically observed for the first time, and the 3sσgFΠu3(υ=0) Rydberg level fully characterized with rotational resolution. The experimental spectroscopic parameters and predissociation level widths suggest strong interactions between the F state and the 3pπuGΠu3 Rydberg and C′Πu3 valence states, analogous to those well known in the case of the isoconfigurational Πu1 states.