We have studied 3s(n-1 and pi-1) Rydberg states and D0(n-1) and D1(pi-1) cationic states of pyrazine [1,4-diazabenzene] by picosecond (2 + 1) resonance-enhanced multiphoton ionization (REMPI), (2 + 1) REMPI photoelectron imaging, He(I) ultraviolet photoelectron spectroscopy (UPS), and vacuum ultraviolet pulsed field ionization photoelectron spectroscopy (VUV-PFI-PE). The new He(I) photoelectron spectrum of pyrazine in a supersonic jet revealed a considerably finer vibrational structure than a previous photoelectron spectrum of pyrazine vapor. We performed Franck-Condon analysis on the observed photoelectron and REMPI spectra in combination with ab initio density functional theory and molecular orbital calculations to determine the equilibrium geometries in the D0 and 3s(n-1) states. The equilibrium geometries were found to differ slightly between the D0 and 3s states, indicating the influence of a Rydberg electron on the molecular structure. The locations of the D1-D0 and 3s(pi-1)-3s(n-1) conical intersections were estimated. From the line width in the D1 <-- S0 spectrum, we estimated the lifetime of D1 to be 12 fs for pyrazine and 15 fs for fully deuterated pyrazine. A similar lifetime was estimated for the 3s(pi-1) state of pyrazine by REMPI spectroscopy. The vibrational feature of D1 observed in the VUV-PFI-PE measurement differed dramatically from that in the UPS spectrum, which suggests that the high-n Rydberg (ZEKE) states converging to the D1 vibronic state are short-lived due to electronic autoionization to the D0 continuum.

The production of N2(B 3Πg, v=0) was identified in the collisional deactivation of N2(a′ 1Σu−, v=0) by Xe, Kr, Ar, O2, and NO. N2(B, v=0) was probed by laser-induced fluorescence via the C 3Πu state. N2(a′, v=0) was produced by energy transfer from N2(a 1Πg, v=0) which was produced by two-photon excitation of N2(X 1Σg+). The rate constant for the intersystem crossing was the largest for Xe and the smallest for Ar. The rate constants relative to that for O2 were 11(Xe), 1.1(Kr), ≈0.001(Ar), and 5.8(NO). Except for NO, the difference in these rate constants is mainly attributable to that in the overall rate constant for the deactivation and the quantum yields are comparable. As for NO, the overall rate constant is one order of magnitude larger than that for O2 and comparable to that for Xe, while the yield for the intersystem crossing is around half of that for O2 or Xe. The rate constants for the intersystem crossing by H2 and CH4 are less than 1% of O2. This is consistent with the high yields for the production of H atoms. The rate constant for N2 is four orders of magnitude smaller than that for O2 and the yield for the intersystem crossing is less than 0.02.

The reactions of N 2 (aЈ 1 ⌺ u Ϫ , vϭ0͒ with H 2 , CH 4 , and their isotopic variants were examined. N 2 (aЈ, vϭ0͒ was produced by energy transfer from N 2 (a 1 ⌸ g , vϭ0͒, while N 2 (a, vϭ0) was produced by two-photon excitation of ground state N 2 . The rate constant for the deactivation of N 2 (aЈ,vϭ0͒ can be determined by measuring the decay profiles of N 2 (a, vϭ0) under the conditions that equilibration between N 2 (a, vϭ0) and N 2 (aЈ, vϭ0) can be assumed. The detection of N 2 (a, vϭ0) was accomplished by a laser-induced fluorescence technique by utilizing the N 2 (bЈ 1 ⌺ u ϩ , vϭ7͒ state as an upper state. The rate constants for the quenching of N 2 (aЈ, v ϭ0͒ by N 2 , H 2 , D 2 , CH 4 , CH 2 D 2 , and CD 4 were determined to be ͑2.0Ϯ0.1͒ϫ10 Ϫ13 , ͑2.8Ϯ0.1͒ ϫ10 Ϫ11 , ͑1.7Ϯ0.1͒ϫ10 Ϫ11 , ͑2.9Ϯ0.2͒ϫ10 Ϫ10 , ͑2.4Ϯ0.3͒ϫ10 Ϫ10 , and ͑2.6Ϯ0.2͒ ϫ10 Ϫ10 cm 3 molecule Ϫ1 s Ϫ1 , respectively. H͑D͒ atoms were identified as reaction products by a two-photon laser-induced fluorescence technique. The yields for the production of H͑D͒ atoms from CH 4 and CD 4 were both determined to be 0.7Ϯ0.2 under the assumption that the only exit for H 2 ͑D 2 ) is the production of two H͑D͒ atoms. No preferential production of H or D atoms was observed in the reaction with CH 2 D 2 , suggesting that the reaction proceeds via bound intermediate complexes.

The deactivation processes of N2(a′ 1Σu−, v = 0), the lowest metastable singlet-state molecular nitrogen, by H2O, D2O, and HOD were investigated. The overall rate constants as well as the quantum yields for the production of H(D) atoms were determined. N2(a′, v = 0) was produced by energy transfer from N2(a 1Πg, v = 0), while N2(a, v = 0) was produced by a two-photon excitation of the ground-state N2. The rate constants for the deactivation by H2O and D2O were determined to be (4.22 ± 0.27) × 10−10 and (4.21 ± 0.11) × 10−10 cm3 s−1, respectively, by measuring the decay profiles of N2(a, v = 0) under equilibrated conditions. The quantum yields for the production of H(D) atoms were determined to be 0.9 −0.2+0.1 both for H2O and D2O under the assumption that the only exit for H2(D2) is the production of two H(D) atoms. In a reaction with HOD, the yield ratio of [H]/[D] was measured to be 1.0 ± 0.1. This lack of the isotope effect suggests that the decomposition proceeds by forming bound intermediate complexes, such as HNNOD and DNNOH.