B3Π State Research Articles

Quantum-resolved dynamics of excited states. Part 2.—Stable levels of the B3Π(0+) state of BrF

The stable, lower vibrational levels (v′⩽ 6) of the excited B3Π(0+) state of 79BrF have been investigated. Laser induced fluorescence has been used to identify individual vibrational and rotational states, as well as to determine their zero-pressure lifetimes τ0 involving the B3Π(0+)–X1Σ+ transition.As a result of this and other work, the vibrational and rotational energies of all accessible states in the B3Π(0+) manifold of 79BrF are known, and a detailed knowledge of the variation of τ0 with v′ and J′ has been obtained. For levels v′⩽ 6, all states are essentially unperturbed, with non-collisional lifetimes τ0 in the range (26.8 ± 2.1) to (40.6 ± 6.9)µs.

Rotational analysis of the B3Π(0+) → X1Σ+ band systems of 35Cl35Cl and 35Cl37Cl in the chlorine afterglow emission spectrum

The B3Π(0+) → X1Σ+ band system of Cl2, excited by the recombination of ground state Cl2P32 atoms at total pressures near 2 Torr, has been rotationally analyzed in the range 6300–9900 Å. About 30 bands, with 0 ≤ v′ ≤ 6 and 5 ≤ v″ ≤ 14, were investigated, mostly for both 35Cl35Cl and 35Cl37Cl. The band origins and rotational constants for the B state were obtained with the help of the known constants for the ground state. The principal molecular constants (cm−1) for the B3Π(0+) state of 35Cl35Cl are as follows: Te′ = 17 817.67(3); ωe′ = 255.38(3); ωe′xe′ = 4.59(1); ωe′ye′ = −0.038(8); De′ = 3341.17(14); Be′ = 0.16313(3); αe′ = 2.42(3) × 10−3; γe′ = −5.7(7) × 10−5. The equilibrium internuclear separation is 2.4311(2) Å. The results of Briggs and Norrish on a transient absorption spectrum of Cl2 assigned as 0g+ ← B3Π(0+) are reinterpreted with the present constants.

Kinetics of excited states of Br2using laser excitation. Part 1 .—System description and rotationally-dependent lifetimes in Br2(B)

A pressure-tuned narrow-band day laser is described. This instrument was used to provide linear scans, free of mode hops, of selected parts of the Br2(B–X) band spectrum in laser-induced fluorescence. Resolution was Doppler limited.Measurements of collision-free lifetimes τ0 of Br2(B) excited molecules were made over a range of rotational states J′, for several vibrational states 23 v′ 11. A strong dependence of Γ0= 1/τ0 upon J′, was found, which was attributed to a heterogeneous predissociation of the emitting B3Π(0+u) state. The results gave a good fit to the relationship, Γ0=ΓR+kv′J′(J′+ 1). The mean value of the radiative, rotation-free lifetime (τR= 1/ΓR) was 8.1 µs for 24 v′ 11.The results show that virtually all band absorption of Br2 between 540 and 590 nm leads to formation of 2P+2P bromine atoms via predissociation.

Quantum-resolved dynamics of excited states. Part 3.—Collision-free lifetimes of BrF(B)

The lifetimes τ0 of resolved ro-vibrational levels (v′, J′) in the exicted B3Π(0+) states of 79BrF and 81BrF have been directly measured under collision-free conditions. Laser-induced flourescence with excitation from a pulsed, narrow-band dye laser has been used to probe all stable vibrational states 8 v′ 0 of the energy manifolds of both isotopic species.The results for v′⩽ 4 and v′= 8 confirm our previous data for τ0 based on Stern-Volmer extrapolations of measurements at higher pressures. For v′= 5, 6, 7, longer τ0 values are now reported. For all rotational states with 5 v′ 0, τ0 values are regular, with only small variations in τ0 in the range 42–56 µs. The lower rotational states of v′= 6 and 7 show similar τ0 values. The results are used to derive transition moment values for the B–X transition of BrF; a small variation of |Re|2 with v′ was found.In the v′= 6, 7 levels, abrupt predissociation commences at the states (6,49) and (7,30); all higher states (6,J′) and (7,J′) have τ0⩽ 100 ns. The predissociating state belongs to Herzberg′s case I(b) with formation of a potential maximum at r≃ 5.3 A. The dissociation energy is thus established within narrow bounds : D00(79BrF)= 20 622 ± 20cm–1 or 246.64 ± 0.24 kJ mol–1; De(BrF)= 20 953 ± 20 cm–1.The lifetime behaviour of the (8,J′) state is dissimillar to that of the (6,J′) and (7,J′) states, in that τ0 for the v′= 8 state varies regularly and strongly with J′. This variation, for rotational energies ⩽ 100 cm–1, gave a good fit to eqn (I) for predissociation, 1/τ0= 1/τ00+kv′J′(J+ 1).

Resonance fluorescence of gaseous chlorine excited with a single longitudinal mode argon ion laser

Resonance fluorescence spectra of gaseous chlorine, excited with a high power single longitudinal mode argon ion laser which was tuned through the lasing profiles of the 4880-, 4965-, 5017-, and 5145-Å lines, were studied. Five progressions of fluorescence lines were found and assigned as the fluorescence of 35Cl35Cl and 37Cl37Cl isotopic molecules resonantly excited from v = 0 and 1 levels of the X1Σ state to the B3Π state. The fluorescence line positions agreed with those of the theoretical calculation within 0.2 cm−1. The fluorescence intensities were very weak due to the extremely small transition probability between the B3Π and the X1Σ states.

Chemiluminescence of Si + N2O flames

Spectra of the chemiluminescent flame produced by the reaction of silicon vapor with N2O have shown strong emission from the A1Π-X1Σ+, b3Π-X1Σ+, and a3Σ+-X1Σ+ systems of SiO with preferential excitation into the b3Π state. Bandhead measurements of 33 bands of the b-X system yielded the following constants for the b3Π state: Te=33947.0±1.9cm−1;ωe=1013.8±1.1cm−1;ωexe=7.57±0.12cm−1. From partially resolved rotational structure in the a-X bands, an approximate value of B = 0.59 ± 0.01cm−1 was obtained for the a3Σ+ state. The effect of adding active nitrogen and CO to the flame was investigated and the results were shown to be consistent with assigning the a and b states as triplets. The photon yield of the Si + N2O reaction was measured and found to be small.

The four-centre reaction I * 2 + F2 studied by laser-induced chemiluminescence in molecular beams

The four-centre reaction between electronically-excited I*2 and ground-state F2 has been studied under crossed-beam conditions by observing the resulting IF* chemiluminescence. The I2* is prepared in the v′= 43 level of the B3Π(0+u) state using the 514.5 nm line of the argon ion laser as an excitation source. The IF* emission is observed to the blue of the laser line and a spectroscopic analysis indicates that the IF* reaction product that is formed in the B3Π(0+) state has a non-Boltzmann vibrational distribution extending to the predissociation limit. For the I*2(B)+ F2(X) reaction, the energetics allow the formation of two IF product molecules, both of which may be electronically-excited, but do not allow the formation of IF*(B)+ I + F. Although the energetically-favourable ground state reaction I2(X)+ F2(X)→ IF(X)+ IF(X) appears not to take place, the reaction I*2(B)+ F2(X)→ IF*(B)+ IF(X or A) occurs with a reaction cross section estimated to be between 10–50 × 10–16 cm2. From the correlation of orbital symmetries (Woodward-Hoffmann rules), the four-centre reaction I2+ F2 as well as I*2+ F2 both appear to be formally forbidden. A discussion is presented suggesting possible ways in which this symmetry restriction for I*2+ F2 can be relaxed.

Kinetics of excited B3Π(0+) states of BrF, ICland IF. Fluorescence decay lifetimes and quenching cross-sections

The fluorescence excited by 8 ns pulses from a tunable dye laser has been used to determine collisional and non-collisional lifetimes of selected vibrational-rotational levels of the B3Π(0+) states of BrF and ICl. Less extensive data on IF are also reported.The results for the non-collisional lifetimes τ0 and the quenching rate constants kM are summarized as follows. [graphic omitted].

The quenching of chlorine fluorescence in the gas phase

Laser induced fluorescence has been observed from the B3Π(O+u) state of chlorine. Lifetimes have been measured from 19 to 208 Pa, but the radiative lifetime is too long to be extracted from the data. A rate coefficient of 3.2 × 10[su13] cm3 mol−1 s−1 was measured for quenching by Cl2 or Ar, the removal process being collision induced predissociation of the 3Π(O+u) state.

B3Π(0+) states of IF, ICl and IBr. Part 2.—Observation and analysis of the excitation spectra of IF and ICl

Narrow band tunable radiation from a nitrogen pumped dye laser has been used to excite fluorescence in the B3Π(0+)–X1∑+ systems of IF (430 to 500 nm) and of ICI (568 to 650 nm). The kinetically labile IF molecules were produced in a fast flow system by the rapid elementary reaction F + ICl → IF + Cl. No laser excitation or absorption spectrum of IF has been described previously. Onset of pre-dissociation has been observed at J′= 12, v′= 10 of IF B3Π(0+), and a new value for the dissociation energy of IF, D″0(IF)⩽(22 700 ± 15) cm–1, is reported. Criteria for the commencement of pre-dissociation in IF spectra are discussed. The mechanism of formation of the B and A states of IF in F2+ I2 systems is considered to arise from initial production of IIF, in the elementary step, I2+ F2→ IIF + F. Laser fluorescence of ICI from the excited B3Π(0+) state (v′= 0, 1, 2) has been observed. The 0–2 band of the B–X system of I35CI has been analysed, providing the first spectro-scopic constants for the level v′= 0 of the B state. A complete evaluation of constants for this shallow, weakly-bound state, has thus been possible. The onset of predissociation in ICI B3Π(0+) near J′= 70 of v′= 2 is discussed in the light of linewidth measurements of other workers.

The a3Σ+ → X1Σ+ and b3Π → X1Σ+ band systems of SiO and the a3Σ+ → X1Σ+ band system of GeO observed in chemiluminescence

Chemiluminescence from SiO and GeO has been produced in a flowing gas system utilizing the reactions Si(3P) + N2O → SiO(b3Π,a3Σ+) + N2 ΔH = −150 kcal/mole Ge(3P) + N2O → GeO(a3Σ+) + N2 ΔH = −130 kcal/mole. An analysis of the chemiluminescence spectrum has shown that the emission originates in the b3Π and a3Σ+ states and terminates in the ground electronic state of SiO. The measured value of the spin–orbit coupling constant for the b3Π state was 75 cm−1. No vibrational constants for either the a3Σ+ or b3Π states could be determined. T0 for the b3Π state was found to be 33 853 cm−1 while that for the a3Σ+ state was found to be 33 409 cm−1. An analysis of the chemiluminescence of GeO was found to originate from the a3Σ+ state and terminate in the electronic ground state. T0 for the a1Σ+ state of GeO was found to be 27 552 cm−1. Good agreement between the experimentally observed vibronic band intensities and those calculated using the Rydberg–Klein method has been obtained.

Rotation–vibrational analysis for three states of NaH and NaD

We have carried out a rotation–vibrational analysis for the X1Σ+, A1Σ+, and b3Π states of NaH and NaD using accurate ab initio calculated potential curves. The calculated values of Be, αe, Re, ωe, and ωexe (with known experimental values in parentheses) are NaH X1Σ+ : Be = 4.748 (4.886) cm−1, αe = 0.126 (0.129) cm−1, Re = 3.625 (3.562) bohr, ωe = 1183.17 (1172.2) cm−1, and ωexe = 21.23 (19.72) cm−1; NaD X1Σ+ : Be = 2.475 (2.5575) cm−1, αe = 0.0474 (0.0520) cm−1, Re = 3.624 (3.565) bohr, ωe = 826.60 (826.10) cm−1 and ωexe = 9.44 cm−1; NaH b3Π : Be = 3.533 cm−1, αe = 0.853 cm−1, Re = 4.202 bohr, ωe = 419.39 cm−1 and ωexe = 50.25 cm−1; NaD b3Π: Be = 1.763 cm−1, αe = 0.265 cm−1, Re = 4.294 bohr, ωe = 311.95 cm−1 and ωexe = 28.68 cm−1. The anomalous behavior of the Bv′s and ΔGv+1/2′s of the A1Σ+ state is satisfactorily reproduced by these calculations: for NaH, Bv (max ) = 1.9717 (1.941) cm−1 at v = 6 (6) and ΔGv+1/2 (max) = 381.37 (360.3) cm−1 at v = 9 (8); for NaD, Bv (max) = 1.0274 (1.012) cm−1 at v = 8 (8) and ΔGv+1/2 (max) = 275.34 (260.22) cm−1 at v = 13 (12). The wavefunctions obtained were also used to calculate average electric dipole moments resulting in the following values (for the lowest rotation–vibrational states): for NaH, μe (X1Σ+) = 2.674 a.u., μe (A1Σ+) = 0.189 a.u., and μe (b3Π) = 0.158 a.u., for NaD, μe (X1Σ+) = 2.668 a.u., μe (A1Σ+) = 0.178 a.u., and μe (b3Π) = 0.163 a.u.

Multiconfiguration self-consistent-field calculation of the dipole moment function and potential curve of NO(X2Π)

The electronic dipole moment function, potential energy curve, and other one−electron properties of the 2Π ground state of NO have been calculated from R = 1.6 to R = 3.4 bohr by the optimized valence configurations (OVC) multiconfiguration self−consistent−field method. At internuclear separations only 0.6−0.7 bohr larger than Re, the ground state wavefunction is found to exhibit a nearly equal mixing of electronic configurations corresponding to the X2Π and B2Π states of NO. This behavior and its manifestations in the OVC framework are discussed in detail. The theoretical OVC−MCSCF dipole curve is shown to be consistent with available experimental data in that (1) its first derivative near Re of 1.10 D/bohr is in excellent agreement with that deduced from observed infrared intensities, and (2) the v = 0 dipole expectation value obtained from the computed moment function and accurate vibrational wavefunctions is −0.139 D (N−O+), which is within 0.02 D of the Stark effect microwave result of ±0.158 D. A comparison of the calculated potential curve with an accurate RKR potential for NO (X2Π) indicates relative congruency to within 0.06 eV over the full range of inernuclear separations spanning the turning points of the v = 25 vibrational level. Comparisons with previous theoretical treatments of this molecule are also presented.

The Electroionization Spectrum of Nitric Oxide

Negative ion resonances having the NO+b3Π, A1Π, c3Π, and B1Π states as grandparents are observed for the first time in the electroionization spectrum of NO. Our results are compared with those from electron transmission experiments. Moreover, some Rydberg states from the series converging to the NO+b3Π state have been analyzed.

Formation of the B3Π(0+) states of BrF and IF by atom recombination in the presence of singlet (1Δg,1Σ+g) oxygen

Combination of F 2P with Br 2P or I 2P ground state atoms in the presence of singlet O21Δg, 1Σ+g, leads to formation of BrF B3Π(0+) or IF B3Π(0+), which were detected by observation of their band emission spectra (975 λ 483 nm), B3Π(0+)→X1Σ+. It was shown that formation of BrF B3Π(0+) explicitly requires energy transfer from O21Δg or 1Σ+g. The most probable excitation process is envisaged to occur by combination of Br 2P+ F 2P atoms (in the presence of a third body) to give BrF A3Π(1)(or possibly 3Π(2, 0–)), followed by collisional energy transfer from singlet oxygen with BrF A3Π(1) to BrF B3Π(0+).At least 38 new bands of the B→X system of BrF have been identified, and the previously uncertain vibrational numbering of the B3Π(0+) state has been confirmed. Vibrational constants are reported for the first time for levels of the X1Σ+ ground state up to v″= 10, corresponding to an energy of 6262 cm–1 above v″= 0. The available data on the dissociation energy of BrF are briefly surveyed, and a value of D°(BrF)= 2.384 eV is favoured.For the B→X system of IF, many new bands have been observed, and vibrational constants for levels up to v″= 19 (10 381 cm–1 above v″= 0) of the ground state are reported.

Molecular constants of the B3Π and A3Σ states of N 2

Molecular constants of the B3Π and A3Σ states of N 2

Population of the higher-lying vibrational levels of the nitrogen B3π state in a glow discharge

The absolute populations of the higher-lying vibrational levels of the B3π state of the nitrogen molecule in a glow discharge have been determined for pressures from 0.1 to 1.0 torr and current densities from 80 to 200 mA/cm2. The absolute concentrations of molecules at levels v′ = 5, 6, ..., 12 under these conditions are of the order of 109–1011 cm−3. The most probable processes leading to a population of the B3π state are thought to be direct electronic impact, cascade transitions, and collisions of normal molecules with molecules in the singlet state.

Electronic excitation of bromine to the B 3?(0 + u ) state in the recombination of ground state Br2 P ? atoms

Emission has been observed from v′⩽ 9 of the B3Π(0+u) state of Br2 formed in the recombination of two ground-state Br(2P) atoms at 298 K and near 1 Torr total pressure of argon. Measurements of relative band intensities of the Br2(B→X) system have been combined with Franck-Condon factors to show that the vibrational population distribution is thermal for 298 K in the range 5 ⩽v′⩽ 9, but that the lower levels 0 ⩽v′⩽ 4 are populated to only a small extent under these conditions. The results suggest that recombination of two Br(2P) atoms into the B3II(0+u) state occurs in the vicinity of v′= 5 via a potential energy barrier of approximately 600 cm–1.

ABSORPTION SPECTRUM OF THE NO MOLECULE: VI. BAND STRUCTURES BELOW 1 600 Å, RYDBERG STATES C2Π, D2Σ+, K2Π, M2Σ+, S2Σ+, NON-RYDBERG STATES B2Π, L2Π AND THEIR INTERACTIONS

The study of the absorption spectrum of the NO molecule has been continued on plates taken in the fourth order of a 10.5-m vacuum spectrograph. The spectra of 14N16O, 15N16O, 14N18O, and 15N18O gases, each kept at liquid-oxygen temperature, were photographed separately. Rotational analyses were carried out for many bands observed below 1 600 Å. Constants for levels of the Rydberg complexes 3p, 4s, 4p, and 5s have been derived. These levels include ν = 5 and ν = 6 of the C2Π state, levels that interact with the levels ν = 21 and 24 respectively of the configurationally different B2Π state. It is shown that the vibrational levels, now well established above the energy where the potential curves of the C and B states cross, are to be attributed to "crossing" curves.The level ν = 4 of the L2Π state, which was discerned in the spectra of the heavier isotopes only, coincides in 14N16O with the level ν = 6 of C2Π and produces a strong three-level perturbation. The level, perturbed in this way, has the appearance of a separate electronic state in 14N16O and at one time was so identified.Many interaction energies are determined, and the new systems of "deper-turbed" levels are thoroughly discussed.

STRUCTURE OF THE BAND SPECTRUM OF CuCl MOLECULE: III. ROTATIONAL STRUCTURE OF THE B AND C SYSTEMS OF Cu65Cl35

The B and C band systems of Cu65Cl35 lying in the region 4600–5200 Å have been photographed in emission under high resolution. Rotational analysis of the (1,0), (0,0), and (0,1) bands of each system has been made. The analysis shows that the B and C systems involve transitions 1Π(B1Π)–X1Σ and 1Σ (C1Σ)–X1Σ respectively. Due to the influence of the closeby C1Σ state, the B1Π state shows appreciable Λ-type doubling. It is found that the B1Π and C1Σ states provide an instance closely resembling the case of Van Vleck's "pure precession". The principal molecular constants obtained for the initial states of the B and C systems of Cu65Cl35 are as follows (cm−1 units):[Formula: see text]