Dispersed fluorescence scans of the A–X(4,v″) and D–X(0,v″) progressions of nitric oxide, after two-photon excitation, are used to determine the electronic transition moments of these band systems. The measured collision free lifetimes of 206±7 ns for A 2Σ+, v′=0, and 18±1 ns for D 2Σ+, v′=0 are used to place transition probabilities on an absolute basis. The branching ratio for D→X is 3.0±0.3 times that for D→A and more than 30 times that for D→C. The ratio of two-photon absorption cross sections for D–X(0,0)/A–X(4,0) is 6±2 and the photoionization probability from D, v′=0 is larger than from A, v′=4 at 375 nm. Also, the two-photon excitation of A–X(4,0) has an unusual intensity distribution, probably due either to interference between intermediate states in the excitation or to anomalies in the photoionization step.

Transition probabilities and electronic transition moments of the A 2Σ+–X 2Π and D 2Σ+–X 2Π systems of nitric oxide

Zero‐kinetic‐energy–photoelectron spectroscopy (ZEKE‐PES) and time‐of‐flight mass spectrometry are used to investigate the near‐threshold, two‐color photoionization of NO via the A 2Σ+, v=0 level. Pulsed‐field ionization of Rydberg states within 20 cm−1 of the ionization threshold is shown to proceed via a diabatic mechanism. Particular emphasis is given to the effect of predissociation on the signal produced by delayed field ionization. A small (∼3 V/cm) dc electric field is shown to produce a dramatic decrease in the field ionization signal in both the NO+‐ion and ZEKE‐electron channels. This decrease is thought to be due to an increase in the predissociation rate caused by the dc electric field. The implications of these experiments for mass‐analyzed threshold ionization are discussed.

Electric field effects in the near-threshold photoionization spectrum of nitric oxide

A spectroscopic database has been constructed for all the contributing electronic systems of air diatomic molecules for elevated temperatures (up to 15,000 K ). The electronic systems which have been investigated are N2 first- and second-positive, Birge–Hopfield 1 and 2, Carroll–Yoshino, Worley and Worley–Jenkins, N2+ Meinel, first- and second-negative, O2 Schumann–Runge and NO γ,β,δ,e,γ′,β′,11,000 A and infrared. The RKR potentials have been reconstructed in order to calculate the vibrational wavefunctions, and the electronic-vibrational part of line intensities has been computed with up-to-date ab-initio electronic transition moment functions. The results of our calculated vibrational band strengths are in good agreement with the available measurements. The positions and intensities of the rotational lines have been determined in intermediate a/b Hund's coupling case with up-to-date molecular constants, and the lambda doubling has been resolved when related parameters were available in the literature. Absorption spectra and the optically thin radiation source strengths of the studied electronic systems are presented and discussed in terms of their comparative contribution to emission and absorption.

Contributions of diatomic molecular electronic systems to heated air radiation

This paper reports on a new two-photon laser-induced fluorescence (TP-LIF) sensor capable of making routine measurements at the few parts per trillion volume level. This direct spectroscopic detection method has been demonstrated to be a reliable instrument while performing both on the ground and in the air. As currently designed it is unique in being 'signal' rather than 'signal-to-noise' limited. The latter characteristic enables the TP-LIF sensor to make atmospheric measurements of NO under environmental conditions that might normally be considered unsuitable for a laser technique. These include clouds, rain, and, in general, high-atmospheric-aerosol loading conditions. Of special interest is the insensitivity of the TP-LIF NO instrument to changes in pressure while operating in the troposphere. This characteristic has enabled this sensor to be used to record real-time altitude profiles of NO. Future improvements should make possible two measurement opportunities: (1) NO flux measurements via the airborne eddy-correlation method and (2) nitrogen isotopic distribution measurements (e.g., (N-15)(0-16) versus (N-14)(0-16) as a means of identifying specific NO(x) sources.

A two-photon laser-induced fluorescence field instrument for ground-based and airborne measurements of atmospheric NO

Two-photon laser-induced fluorescence of the NO A–X(0–5,0) and D–X(0–3,0) bands is used to obtain collision-free lifetimes of the A v′=0–5 and D v′=0–3 levels in a flow cell. The vibrational trend from NO A v′=0 to v′=3 is small, with radiative lifetimes between 205±7 to 184±8 ns, respectively, in agreement with recent calculations derived from branching ratio measurements and ab initio calculations. Rotationally resolved measurements in the NO A 2Σ+ and D 2Σ+ states reveal very different lifetime behavior for these nearly isoenergetic levels above the NO X 2Π state dissociation limit. The rotational lifetimes of A 2Σ+v′=4,5 and D 2Σ+v′=0 are basically constant with rotation. However, D 2Σ+v′=1, 2, and 3 have a strong rotational dependence, decreasing nearly threefold between N′=0 and 20. These observations suggest weak coupling with the ground-state continuum to be the most likely predissociation mechanism for the high A 2Σ+ levels, and rotational on heterogeneous (gyroscopic) predissociation by the C 2Π...

Radiative and predissociative rates for NO A 2Σ+v′=0–5 and D 2Σ+v′=0–3

The D 2Σ+ → A 2Σ+, E 2Σ+ → D 2Σ+ and E 2Σ+ → A 2Σ+ systems of NO have been recorded at high resolution by Fourier transform spectroscopy. Numerous small perturbations in the A and D states are observed for the first time. Accurate energy term values are obtained for the A 2Σ+ (v = 0 to 4), D 2Σ+ (v = 0 to 4) and E 2Σ+ (v = 0 to 2) vibrational levels.

https://iopscience.iop.org/article/10.1088/0031-8949/26/6/003/pdf

C Amiot

Papers

Fourier Transform Spectrometry of the D2Σ+-A2Σ+ E2 Σ+-D2 Σ+ and E2Σ+-A2Σ+ and Systems of Nitric Oxide