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Branching ratios for N(2D03/2) and N(2D05/2) produced by predissociation of state selected excited nitrogen molecules in the vacuum ultraviolet region have been measured for the first time. The quantum numbers of the excited nitrogen molecule are defined by selective excitation of the nitrogen molecule in the Franck–Condon region from the ground electronic, 1Σg+, vibrational, v″, and rotational, J″ state to an excited Eu′, v′, J′ state with a tunable vacuum ultraviolet, VUV1, laser. The neutral atoms produced by predissociation from this excited state are then selectively ionized with a second tunable VUV2laser. Measurement of the relative populations of these two atoms formed in their spin–orbit states defines the quantum states for the atomic products. This means that the wave functions of the initial state and knowledge of the relative yields define all the experimental parameters for this series of unimolecular reactions. The ions formed by VUV2are mass analyzed with a time-of-flight mass spectrometer and detected with a time slice velocity ion imaging mass spectrometer. In this manner, we can determine the recoil velocity associated with the predissociation process. Two different techniques are used to determine the spin–orbit ratios, namely, resonant VUV photoionization (RVUV-PI) spectroscopy and total kinetic energy release (TKER) spectroscopy determined from the image produced when the atoms are selectively ionized by VUV2in the interaction region. The TKER spectra obtained from the lines at 110 296.25 and 110 304.96 cm−1that couple to a newly discovered autoionization line at 129 529.4255 ± 0.0015 cm−1prove that the lines observed in this region originate from the N(2D03/2) and N(2D05/2) atoms. Two other lines in this region at 110 286.20 and 110 299.89 cm–1originate from the nitrogen N(4S03/2) that is photoionized in a 1+ 1 VUV–UV resonant multiphoton ionization process. The spin–orbit branching ratios have been evaluated for valence and Rydberg electronic excited states from 104 129.4 to 118 772.1 cm–1, and it shows that they are independent of the rotational and vibrational quantum numbers. They are not appreciably affected by the symmetry properties of the wave function in the Franck–Condon region of the excited states. In the energy region below 117 153.8 cm–1the pathways at long internuclear distances appear to determine [N(2D03/2)]/[N(2D05/2)] branching ratios of ∼0.38, ∼0.62, and ∼1.04. At higher energies, TKER and RVUV-PI spectroscopy have been used to show that the average fraction of the N(2D03/2) and N(2D05/2) atoms produced in the spin-allowed channels that produce two N(2D0J) is 0.85 versus 0.15 for spin-forbidden channels. The importance and need for this information for comparison with theory and applications in astrochemistry are briefly discussed.

Collisional removal of electronic energy from O2in the low-lying a1Δgstate is typically an extremely slow process for the v= 0 level. In this study, we report results on the deactivation of O2(a1Δg, v= 1–3) in collisions with O2and CO2. Ozone photodissociation in the 200–310 nm Hartley band is the source of O2(a, v), and resonance-enhanced multiphoton ionization is used to probe the vibrational-level populations. Deactivation of the a(v= 1–3) levels in collisions with O2at 300 K is fast, with rate coefficients of (5.6 ± 1.1) × 10–11, (3.6 ± 0.4) × 10–11, and (1.9 ± 0.4) × 10–11cm3s–1(2σ) for v= 1, 2, and 3, respectively. The relaxation process appears to involve a near-resonant electronic energy transfer pathway analogous to that observed in vibrationally excited O2(b1Σg+). With CO2collider gas, the removal rate coefficient at 300 K is (1.8 ± 0.4) × 10–14and (4.4 ± 0.6) × 10–14cm3s–1(2σ) for v= 1 and 2, respectively. Despite the small mole fraction of O2in the atmospheres of Mars and Venus, O2is at least as important as CO2in the final stages of collisional relaxation within the O2vibrational-level manifold.

The recently discovered fast, multiquantum OH(v)+O(3P) vibrational‐to‐electronic relaxation mechanism provided new insight into the OH(v) Meinel band nighttime emission formation. Using a new detailed OH(v) model and novel retrieval algorithm, we obtained O(3P) densities in the nighttime mesosphere and lower thermosphere (MLT) from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) 2.0‐ and 1.6‐μm radiances. We demonstrate how critical the new OH(v) relaxation mechanism is in the estimation of the abundance of O(3P) in the nighttime MLT. Furthermore, the inclusion of this mechanism enables us to reconcile historically large discrepancies with O(3P) results in the MLT obtained with different physical models and retrieval techniques from WIND Imaging Interferometer, Optical Spectrograph and Infrared Imager System, and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography observations of other airglow emissions. Whereas previous SABER O(3P) densities were up to 60% higher compared to other measurements the new retrievals agree with them within the range (±25%) of retrieval uncertainties. We also elaborate on the implications of this outcome for the aeronomy and energy budget of the MLT region. The recently discovered fast hydroxyl‐atomic oxygen relaxation mechanism provided new insight into the mesospheric emission formation. Using a new hydroxyl (OH) model and retrieval algorithm, we obtained atomic oxygen concentration in the nighttime mesosphere and lower thermosphere (MLT) from the SABER OH radiances. We demonstrate how critical this new relaxation mechanism is in the estimation of the abundance of atomic oxygen in the nighttime MLT. Furthermore, the inclusion of this mechanism enables us to reconcile historically large discrepancies with atomic oxygen results in the MLT obtained with different physical models and retrieval techniques from WINDII, OSIRIS, and SCIAMACHY observations of other airglow emissions. Whereas previous SABER atomic oxygen densities were up to 60% higher compared to other measurements, the new retrievals agree with them within the range (±25%) of retrieval uncertainties. We also elaborate on the implications of this outcome for the aeronomy and energy budget of the MLT region. New detailed non‐LTE OH(v) model is applied to analyze SABER nighttime Meinel band emissionsNovel two‐channel O(3P) retrieval technique uses SABER nighttime 2.0‐ and 1.6‐micrometer radiancesNew retrievals reconcile large differences with O(3P) derived from other airglows

On the basis of experimental and theoretical studies, this paper proposes a new mechanism that contributes to nocturnal 4.3 µm CO2emissions. It suggests that collisions of ground state O atoms with highly vibrationally excited OH(v), produced by the reaction of H with O3, remove a substantial fraction of the OH(v) vibrational energy by a fast, spin‐allowed, multiquantum vibration‐to‐electronic energy transfer (ET) process that generates O(1D): OH(v≥ 5) + O(3P) → OH(0 ≤ v′ ≤ v− 5) + O(1D). The electronically excited O(1D) atom is subsequently deactivated by collisions with N2in a fast spin‐forbidden ET process that leaves the N2molecule with an average of 2.2 vibrational quanta. Finally, the vibrational excitation of N2is transferred by a fast, near‐resonant vibration‐to‐vibration ET process to the asymmetric stretch (v3) mode of CO2, which promptly radiates near 4.3 µm. Fixes 4.3 µm radiance model of nocturnal mesosphereBased on experimental and theoretical evidence proposes a new mechanismPoint out implications of new mechanism on energy budget of mesosphere

We report stimulated Brillouin and Rayleigh scattering experiments in n-hexane for a wide range of subcritical and supercritical temperature and pressure conditions, including the near-critical region. The measurements were performed in a cell designed for operation at conditions near or above the critical point. An injection-seeded Nd:YAG laser was employed as the pump laser and an external cavity diode laser as the probe laser. The use of 1064-nm light enhances stimulated Rayleigh scattering through direct thermal absorption. Analysis of the recorded spectra yielded the widths, shifts, and heights of the electrostrictive Brillouin, thermal Brillouin, and thermal Rayleigh peaks. Comparison of these features with theory has showed consistency with the theoretical predictions of the relationships between the heights and widths of the thermal Brillouin and thermal Rayleigh peaks. Remarkable structure and sudden changes in the behavior of the Brillouin shifts, widths, and heights were observed in the vicinity of the critical region.

Retrieving the total number density [OH], which is used in the chemical balance equations and is the sum of both ground and excited vibrational state populations, is a challenging problem to such a degree there exist no such estimates from recent space observations. We present a novel retrieval approach to simultaneously and self‐consistently derive both [O(3P)] and total [OH] in the nighttime mesosphere and lower thermosphere which operates with the Meinel band volume emission rates and their ratios. Its application to the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) and Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) observations shows a good agreement of the retrieved [O(3P)] taking into account the measurement uncertainties and variation of model inputs used. However, retrieved [OH] show a large discrepancy, mainly above 90 km. SCIAMACHY [OH] is generally in good agreement with WACCM [OH] after accounting for uncertainties, while SABER OH is larger than WACCM [OH] by up to a factor of 2. The hydroxyl molecule plays an important role in the physics, chemistry, and dynamics of the middle and upper atmosphere region (60–120 km). Obtaining total hydroxyl density from its molecular emissions is a challenging problem to such a degree there exist no such estimates from the recent space observations. We present a novel approach to obtain both atomic oxygen and total hydroxyl densities in the middle and upper atmosphere from nighttime observations of the hydroxyl molecular emissions. We apply the new approach to two different space‐based instrument observations of hydroxyl emissions at multiple infrared wavelengths. The atomic oxygen densities obtained from the two instruments using our new approach are in good agreement after taking into account uncertainties, while the hydroxyl densities show a large discrepancy. A novel approach to the simultaneous retrieval of nighttime O(3P) and OH densities from space‐based satellite observations is presentedTotal OH densities are retrieved for the first time in the mesosphere and lower thermosphere (MLT)Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY retrieved OH densities are comparable to chemical models in the MLT while Sounding of the Atmosphere using Broadband Emission Radiometry retrieved OH densities are higher A novel approach to the simultaneous retrieval of nighttime O(3P) and OH densities from space‐based satellite observations is presented Total OH densities are retrieved for the first time in the mesosphere and lower thermosphere (MLT) Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY retrieved OH densities are comparable to chemical models in the MLT while Sounding of the Atmosphere using Broadband Emission Radiometry retrieved OH densities are higher

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