A.M. Pravilov

The “approach-induced” and collision-induced transitions from low, vE=8–23, vibronic levels of the I2(E) state

Abstract The dependences of the I 2 ( E0 g + ,v E ,J E → I 2 ( X ) D0 u + ,v D ,J D ) transition rate constants on the vibrational v E , v D , rotational J E , J D quantum numbers, energy gaps, and Franck–Condon factors of the combined levels have been studied in the range v E =8–23. The extremely long-range near-resonance I 2 ( E ,v E → I 2 ( X ) D ,v D ) process as well as nonresonant transitions, corresponding to the energy loss up to ΔE=240 cm −1 (approximately three quanta of vibrational energy), have been observed. Total cross-section of the latter is up to 12 times less than the maximum one of the extremely long-range transition. It has been shown that cross-sections of the processes are independent of initial J E number. The u↔g and ΔΩ=0 propensity rules are valid in the I 2 ( E ) → I 2 ( X ) I 2 (ion-pair states) transitions. The vibrational and rotational populations of the D state levels depend on v E and ΔE . Mechanism of the processes under study has been discussed. It has been shown that essentially nonresonant transitions occur after a mutual I 2 (E) and I 2 (X) capture in orbiting-controlled collision complex. Maybe, one has to take into account relativistic (magnetic) interactions for description of the extremely long-range transitions.

The collision-induced transitions, M=He, Ar, N2, CF4

Abstract The dependences of the I 2 ( E0 g + ,v E ,J E → M D0 u + ,v D ,J D ) , M=He, Ar, N2,CF4, transition rate constants on the vibrational vE, vD, rotational JE, JD quantum numbers, energy gaps, as well as their correlations with Franck–Condon factors of the initial and final levels have been studied. Intramolecular transitions induced by the C3/R3 term of multipole series of potential energy operator instantaneous dipole (I2(E–D) optical transition) – instantaneous dipole (vibrational transitions in CF4 molecule) have been found out and discussed. The collision-induced intramolecular transitions observed in this and our previous works [Chem. Phys. 242 (1999) 263, 263 (2001) 459 and Chem. Phys. 277 (2002) 179] have been classified.

Collision-induced nonadiabatic transitions in the second-tier ion-pair states of iodine molecule: Experimental and theoretical study of the I2(f0g+) collisions with rare gas atoms

Nonadiabatic transitions induced by collisions with He, Ar, Kr, and Xe atoms in the I(2) molecule excited to the f0(g)(+) second-tier ion-pair state are investigated by means of the optical-optical double resonance spectroscopy. Fluorescence spectra reveal that the transition to the F0(u)(+) state is a dominant nonradiative decay channel for f state in He, Ar, and Kr, whereas the reactive quenching is more efficient for collisions with Xe atom. Total rate constants and vibrational product state distributions for the f-->F electronic energy transfer are determined and analyzed in terms of energy gaps and Franck-Condon factors for the combining vibronic levels at initial vibrational excitations v(f)=8, 10, 14, and 17. Quantum scattering calculations are performed for collisions with He and Ar atoms, implementing a combination of the diatomics-in-molecule and long-range perturbation theories to evaluate diabatic PESs and coupling matrix elements. Calculated rate constants and vibrational product state distributions agree well with the measured ones, especially in case of Ar. Qualitative comparison is made with the previous results for the second-tier f0(g)(+)-->F0(u)(+) transition in collisions with I(2)(X) molecule and the first-tier E0(g)(+)-->D0(u)(+) transition induced by collisions with the rare gas atoms.

The mechanism of N2(B3Πg) deactivation by N2

Abstract A study of the mechanism for N 2 (B 3 Π g ) deactivation by N 2 has been carried out using chemiluminescence in the reaction N( 4 S) + N( 4 S)(+M) → N 2 (B 3 Π g , ν′ → N 2 (A 3 Σ u + , ν″) + hv . Different N 2 isotopes were used as excited and third-body molecules. N 2 (B 3 Π g , ν) deactivation was found to involve electronic energy transfer: 15 N 2 (B 3 Π g , ν 1 ) + 14 N 2 (X 1 Σ g + , 0) → 15 N 2 (X 1 Σ g + , ν 2 ) + 14 N 2 (B 3 Π g , ν 3 ).

Hyperfine coupling of the iodine E0+g, vE = 19 and γ1u, vγ = 18 ion-pair states

A considerable difference of iodine emission spectra after optical–optical double resonance excitation of the E0+g, vE = 19, JE ≈ 55 and JE ≈ 85 rovibronic levels is observed. The latter include strong transitions from the γ1u ion-pair state to valence ones. This feature is interpreted as a result of hyperfine coupling of near-resonant E0+g, vE = 19, JE = 81 and γ1u, vγ = 18, Jγ = 80 states. The hyperfine matrix element and dipole moment functions of transitions from the γ state are estimated. The hyperfine g/u mixing of the iodine ion-pair states is observed for the first time.

Anomalously large isotope effect in the chemiluminescence from N(4S) + O(3P) recombination

Abstract The effect of isotopic substitution on the chemiluminescence that occurs during the recombination of the N( 4 S) and O( 3 P) atoms has been studied for the following isotope combinations: 14 N + 16 O, 15 N + 16 O, 14 N + 18 O, 15 N + 18 O. Emissions in the NO δ, γ, β and Ogawa bands were identified in the spectra. Isotopic substitution caused remarkable changes in the vibrational distribution and intensity of the emission from the NO(B 2 Π) state (β bands). This effect can be explained by the isotopic shift of those vibrational levels of the B state relative to the a 4 Π state which are populated via the gateway mechanism.

Non-adiabatic transitions from I2(E0g+ and D0u+) states induced by collisions with M = I2(X0g+) and H2O

The stepwise two-step two-color and three-step three-color laser excitation schemes are used for selective population of rovibronic levels of the first-tier ion-pair E0(g)(+) and D0(u)(+) states of molecular iodine and studies of non-adiabatic transitions to the D and E states induced by collisions with M = I(2)(X) and H(2)O. Collection and analysis of the luminescence after excitation of the v(E) = 8, 13 and v(D) = 13, 18 vibronic levels of the E and D states in the pure iodine vapor and the gas-phase mixtures with H(2)O provide rate constants for the non-adiabatic transitions to the D and E state induced by collisions with these molecules. Vibrational distributions for the [formula: see text] collision-induced non-adiabatic transitions (CINATs) are obtained. Rather strong λ(lum)(max) ≈ 3400 Å luminescence band is observed in the I(2) + H(2)O mixtures, whereas its intensity is ~100 times less in pure iodine vapor. Radiative lifetimes and quenching rate constants of the I(2)(E,v(E) = 8, 13 and D,v(D) = 13, 18) vibronic state are also determined. Rate constants of the [formula: see text], v(E) = 8-54, CINATs are measured again and compared with those obtained earlier. New data confirm resonance characters of the CINATs found in our laboratory about 10 years ago. Possible reasons of differences between rate constant values obtained in this and earlier works are discussed. It is shown, in particular, that differences in rate constants of non-resonant CINATs are due to admixture of water vapor in iodine.

Kinetics of photorecombination of N(4S) atoms. Vegard-Kaplan bands

Abstract The spectrum and rate constant for the recombination of nitrogen atoms via the reaction N(4S) + N(4S) + M → N2 (A 3Σu+) + M → N2(X 1Σg+) + M + hv is obtained. The mechanism for population of low vibrational levels of N2(A 3Σu+) is discussed.

Spectroscopic constants and potential energy curve of the iodine weakly bound 1u state correlating with the I(2P1/2) + I(2P1/2) dissociation limit

The stepwise three-step three-color laser population of the I2(β1g, νβ, Jβ) rovibronic states via the , νB, JB rovibronic states and rovibronic levels of the 1u(bb) and (bb) states mixed by hyperfine interaction is used for determination of rovibronic level energies of the weakly bound I2(1u(bb)) state. Dunham coefficients of the state, Yi0 (i = 0–3), Yi1 (i = 0–2), Y02 and Y12 for the = 1–5, 8, 10, 15 and ≈ 9–87 ranges, the dissociation energy of the state, De, and equilibrium I–I distance, Re, as well as the potential energy curve are determined. There are aperiodicities in the excitation spectrum corresponding to the β, νβ = 23, Jβ ← 1u(bb), ν1u = 4, 5, J1u progressions in the I2 + Rg = He, Ar mixture, namely, a great number of lines which do not coincide with the R or P line progressions. Their positions conflict with the ΔJ-even selection rule. Furthermore, they do not correspond to the ΔJ-odd progression.

Ion-pair states in the complexes of iodine molecule with rare gases

The luminescence excitation spectra and the luminescence spectra of the I2 + Rg (Rg = He, Ar, Xe; pRg = 2–20 Torr) mixtures measured at room temperature by the method of double optical resonance in the spectral range corresponding to the population of the I2(f0g+, vf = 8.9) levels and in its vicinity are analyzed in this work. The experimental data and their interpretation, according to which these spectra can be explained by the energy transfer in the intermediate I2(B0u+) and final I2(f0g+) states of the free iodine molecule rather than by the optical population, luminescence, and predissociation of the ion-pair RgI2(IP) complexes, are discussed. It is shown that these data can be explained only with account taken of the optical population of the RgI2(IP) complexes.