Predissociative decay of the c′41Σu+, v = 0 state of N2

Vacuum ultraviolet photoexcitation and photofragment spectroscopic studies of 14N15N between 109000 and 117500 cm-1

In this study, we employed a newly built time-slice velocity-map ion imaging setup, equipped with two tunable vacuum ultraviolet (VUV) laser sources, to obtain the first comprehensive high-resolution photoexcitation and photofragment excitation spectra of ¹⁴N¹⁵N in the VUV photon energy range 109 000-117 500 cm^-1. The spectroscopic simulation program PGOPHER was used to analyze the rotationally resolved spectra. Band origins, rotational constants, and isotope shifts compared with those of ¹⁴N₂ have been obtained for 31 electric-dipole-allowed vibrational states of ¹⁴N¹⁵N in the aforementioned energy range. These spectroscopic parameters are found to depend on the vibrational quantum number irregularly. Systematic perturbations of the rotational transition energies and predissociation rates within individual absorption bands have also been observed. These are proved to be caused by the strong homogeneous interactions between the valence b'¹Σ_u ⁺ state and the Rydberg c_n ^{' 1}Σ_u ⁺ states, and between the valence b¹Π_u states and the Rydberg o₃ ¹Π_u states. Heterogeneous interactions between the Rydberg c_n ¹Π_u states and c_n ^{' 1}Σ_u ⁺ states also play an important role.

High-resolution Fourier-transform extreme ultraviolet photoabsorption spectroscopy of 14N15N

The first comprehensive high-resolution photoabsorption spectrum of (14)N(15)N has been recorded using the Fourier-transform spectrometer attached to the Desirs beamline at the Soleil synchrotron. Observations are made in the extreme ultraviolet and span 100 000-109 000 cm(-1) (100-91.7 nm). The observed absorption lines have been assigned to 25 bands and reduced to a set of transition energies, f values, and linewidths. This analysis has verified the predictions of a theoretical model of N(2) that simulates its photoabsorption and photodissociation cross section by solution of an isotopomer independent formulation of the coupled-channel Schrödinger equation. The mass dependence of predissociation linewidths and oscillator strengths is clearly evident and many local perturbations of transition energies, strengths, and widths within individual rotational series have been observed.

Time-resolved study of excited states of N2 near its first ionization threshold

Two-photon, two-color double-resonance ionization spectroscopy combining synchrotron vacuum ultraviolet radiation with a tunable near-infrared (NIR) laser has been used to investigate gerade symmetry states of the nitrogen molecule. The rotationally resolved spectrum of an autoionizing (1)Σ(g)(-) state has been excited via the intermediate c(4) (v = 0) (1)Π(u) Rydberg state. We present the analysis of the band located at T(v) = 10,800.7 ± 2 cm(-1) with respect to the intermediate state, 126,366 ± 11 cm(-1) with respect to the ground state, approximately 700 cm(-1) above the first ionization threshold. From the analysis a rotational constant of B(v) = 1.700 ± 0.005 cm(-1) has been determined for this band. Making use of the pulsed structure of the two radiation beams, lifetimes of several rotational levels of the intermediate state have been measured. We also report rotationally-averaged fluorescence lifetimes (300 K) of several excited electronic states accessible from the ground state by absorption of one photon in the range of 13.85-14.9 eV. The averaged lifetimes of the c(4) (0) and c(5) (0) states are 5.6 and 4.4 ns, respectively, while the b(') (12), c(')(4) (4, 5, 6), and c(')(5) (0) states all have lifetimes in the range of hundreds of picoseconds.

N(2) band oscillator strengths at near-threshold energies

Band oscillator strengths for 58 bands in the near-threshold region of N(2), i.e., from 116 200 to 125 400 cm(-1), are derived from measured band-integrated optical depths. The complexity of the absorption spectrum demands that the measurements be carried out on rotationally cold supersonic jet expansions. The column density N in the absorbing path of the jet cannot be measured directly. Instead, the room temperature f values of selected calibration bands are used to convert the band-integrated optical depths of the jet-cooled calibration bands to preliminary column densities [N], which, plotted as a function of jet reservoir pressure p, scatter around a straight line passing through the origin of the graph. From the slope of the line, first estimates of the effective column density N can be derived for any value of p. Second estimates are obtained by repeating the same procedure using ab initio calculated f values based on the work of Spelsberg and Meyer [J. Chem. Phys. 115, 6438 (2001)]. Depending on the jet configuration, the two estimates differ by 3%-15%; their average is accepted as the best approximation to N. The derived band oscillator strengths are compatible with ab initio results of Spelsberg and Meyer and reproduce the observations reasonably well, even where two or more transitions combine in the formation of complex band structures. They also clarify the analysis of the absorption spectrum in the region of the 7p(0) complex [Jungen, Huber, Jungen, and Stark, J. Chem. Phys. 118, 4517 (2003)] and lead to a plausible interpretation of the spectrum in the 124 680-124 880 cm(-1) range. As a result, the lowest three vibronic levels of both the 3(')d(')sigma and the 4(')s(')sigma core excited states have now been identified.

Fluorescence excitation spectra of the bΠu1, b′Σu+1, cnΠu1, and cn′Σu+1 states of N2 in the 80–100nm region

Fluorescence excitation spectra produced through photoexcitation of N(2) using synchrotron radiation in the spectral region between 80 and 100 nm have been studied. Two broadband detectors were employed to simultaneously monitor fluorescence in the 115-320 nm and 300-700 nm regions, respectively. The peaks in the vacuum ultraviolet fluorescence excitation spectra are found to correspond to excitation of absorption transitions from the ground electronic state to the b (1)Pi(u), b(') (1)Sigma(u) (+), c(n) (1)Pi(u) (with n=4-8), c(n) (') (1)Sigma(u) (+) (with n=5-9), and c(4) (')(v('))(1)Sigma(u) (+) (with v(')=0-8) states of N(2). The relative fluorescence production cross sections for the observed peaks are determined. No fluorescence has been produced through excitation of the most dominating absorption features of the b-X transition except for the (1,0), (5,0), (6,0), and (7,0) bands, in excellent agreement with recent lifetime measurements and theoretical calculations. Fluorescence peaks, which correlate with the long vibrational progressions of the c(4) (') (1)Sigma(u) (+) (with v(')=0-8) and the b(') (1)Sigma(u) (+) (with v(') up to 19), have been observed. The present results provide important information for further unraveling of complicated and intriguing interactions among the excited electronic states of N(2). Furthermore, solar photon excitation of N(2) leading to the production of c(4) (')(0) may provide useful data required for evaluating and analyzing dayglow models relevant to the interpretation of c(4) (')(0) in the atmospheres of Earth, Jupiter, Saturn, Titan, and Triton.

Oscillator strength and linewidth measurements of dipole-allowed transitions in N214 between 93.5 and 99.5nm

Line oscillator strengths in 16 electric dipole-allowed bands of 14N2 in the 93.5-99.5 nm (106,950-100,500 cm(-1)) region have been measured at an instrumental resolution of 6.5 x 10(-4) nm (0.7 cm(-1)). The transitions terminate on vibrational levels of the 3psigma 1Sigma u (+), 3ppi 1Pi u, and 3ssigma 1Pi u Rydberg states and of the b' 1Sigma u (+) and b 1Pi u valence states. The J dependences of band f values derived from the experimental line f values are reported as polynomials in J'(J'+1) and are extrapolated to J'=0 in order to facilitate comparisons with results of coupled-Schrodinger-equation calculations that do not take into account rotational interactions. Most bands in this study reveal a marked J dependence of the f values and/or display anomalous P-, Q- and R-branch intensity patterns. These patterns should help inform future spectroscopic models that incorporate rotational effects, and these are critical for the construction of realistic atmospheric radiative transfer models. Linewidth measurements are reported for four bands. Information provided by the J dependences of the experimental linewidths should be of use in the development of a more complete understanding of the predissociation mechanisms in N2.

Isotopic variation of experimental lifetimes for the lowest Πu1 states of N2

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 14N2 b 1Πu(v=1)

The lifetime of the b 1Piu(v=1) state in 14N2 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 approximately 28% for this level of the b state.