Mid-Infrared Amplified Spontaneous Emission from the f' 0g+ (1D2) Ion-Pair State and Spectroscopic Characterization of the Shallow 0g+ (ab) Valence State of I2.

In this paper, we describe amplified spontaneous emission (ASE) from the f' 0g+ (1D2) ion-pair state of I2 populated through a two-step laser excitation technique via the B 3Π(0u+) valence state. The intense infrared emission propagating in the direction of the incident laser beam is assigned to the ASE transition from the f' 0g+ (1D2) state to the F' 0u+ (1D2) ion-pair state. The subsequent ultraviolet fluorescence transition from the F' 0u+ (1D2) state to the 0g+ (bb) state as well as the 0g+ (ab) state is also reported. By Franck-Condon simulation of the cascading F' 0u+ (1D2) → 0g+ (bb) band, we determine the population distributions in the F' 0u+ (1D2) state generated by ASE, which are consistent with the intensity profile of the mid-infrared ASE spectrum. Finally, employing these vibrational distributions for the F' 0u+ (1D2) state, spectral parameters for the shallow 0g+ (ab) state are derived.

Collision induced state-to-state energy transfer dynamics between the 2u ((1)D2) and 2g ((1)D2) ion-pair states of I2.

We report the first observation of collision induced state-to-state energy transfer from the 2u ((1)D2) (v2u = 3-7) ion-pair state of I2 using a perturbation facilitated optical-optical double resonance technique through the c (1)Πg∼ B (3)Π(0) hyperfine mixed double-faced valence state as the intermediate state. The excitation of the 2u ((1)D2) state yielded the weak UV fluorescence from the wide range of vibrational levels in the nearby 2g ((1)D2) state. The vibrational distribution in the 2g ((1)D2) state derived by the Franck-Condon simulation of the UV fluorescence showed that the population in the 2u ((1)D2) state transfers mostly to the 2g ((1)D2) vibronic levels which are located energetically above the laser-prepared level. The radiative lifetimes and the self-quenching rate constants were determined to be 21.3 ± 0.1 and 44.6 ± 0.8 ns, and (1.30 ± 0.01) × 10(-9) and (2.26 ± 0.17) × 10(-9) cm(3) molecule(-1) s(-1) for the 2u ((1)D2) (v2u = 3) and 2g ((1)D2) (v2g = 5) states, respectively. The rate constant for the 2u ((1)D2) - 2g ((1)D2) collision induced state-to-state energy transfer was also evaluated to be (1.89 ± 0.01), (3.07 ± 0.07), and (3.77 ± 0.05) × 10(-10) cm(3) molecule(-1) s(-1) for the v2u = 3, 5, and 7 levels, respectively. The very large self-quenching cross sections for the ion-pair states of I2 could be explained by the harpoon mechanism.

Infrared amplified spontaneous emission from the 0 ((3)P0) and 0 ((1)D2) ion-pair states of molecular bromine.

We report the observation of amplified spontaneous emission for the first time from the 0 ((3)P0) and 0 ((1)D2) ion-pair states of Br2 by using an optical-optical double resonance technique through the B (3)Π(0) valence state as the intermediate state. The strong infrared emission propagating along the incident laser radiation is assigned to the parallel ASE transitions from the 0 ion-pair states down to the nearby 0 ion-pair states. The subsequent UV fluorescence from the 0 states to the high vibrational levels of the ground state is also observed. By the Franck-Condon simulation of the cascade UV fluorescence, we determine the vibrational distributions in the 0 states populated by ASE, which are consistent with the intensity distribution in the dispersed infrared ASE spectrum. The lifetimes of the relevant ion-pair states are evaluated by analyzing the temporal profiles of the UV fluorescence.

Dispersed fluorescence spectroscopy of the SiCN Ã2Δ - X̃2Π system: Observation of some vibrational levels with chaotic characteristics.

The laser induced fluorescence (LIF) spectrum of the à 2Δ - X̃ 2Π transition was obtained for SiCN generated by laser ablation under supersonic free jet expansion. The vibrational structures of the dispersed fluorescence (DF) spectra from single vibronic levels (SVL's) were analyzed with consideration of the Renner-Teller (R-T) interaction. Analysis of the pure bending (ν2) structure by a perturbation approach including R-T, anharmonicity, spin-orbit (SO), and Herzberg-Teller (H-T) interactions indicated considerably different spin splitting for the µ and κ levels of the X̃ 2Π state of SiCN, in contrast to identical spin splitting for general species derived from the perturbation approach, where µ and κ specify the lower and upper levels, respectively, separated by R-T. Further analysis of the vibrational structure including R-T, anharmonicity, SO, H-T, Fermi, and Sears interactions was carried out via a direct diagonalization procedure, where Sears resonance is a second-order interaction combined from SO and H-T interactions with Δ K = ± 1, ΔΣ = ∓1, and Δ P = 0, and where P is a quantum number, P = K + Σ. The later numerical analysis reproduced the observed structure, not only the pure ν2 structure but also the combination structure of the ν2 and the Si-CN stretching (ν3) modes. As an example, the analysis demonstrates Sears resonance between vibronic levels, (0110) κ Σ(+) and (0200)µΠ12, with Δ K = ± 1 and Δ P = 0. On the basis of coefficients of their eigen vectors derived from the numerical analysis, it is interpreted as an almost one-to-one mixing between the two levels. The mixing coefficients of the two vibronic levels agree with those obtained from computational studies. The numerical analysis also indicates that some of the vibronic levels show chaotic characteristics in view of the two-dimensional harmonic oscillator (2D-HO) basis which is used as the basis function in the present numerical analysis; i.e., the eigen vectors for some of the observed levels have several components of the basis, and we have not been able to give precise vibronic assignments for the levels, but just vibronically labeled, referring the largest component in their vectors. (To emphasize this situation, we do not use the word "assignment," but prefer to use "label" as the meaning of just "label," but not "assign," throughout this paper.) The latter shows that the vibronic labels of the levels are meaningless, and the P quantum number and the order of their eigen states in the P matrix block derived in the numerical analysis only characterize the vibronic levels. Comparing the constants obtained for all of the interactions with those of species showing Sears resonance and studied previously, it is found that none of them are strong, but are moderate. It is thus concluded that the chaotic appearance is not derived by any strong interaction, but is induced by complex and accidental proximities of the vibronic levels caused by the moderate interactions.

Electronic spectrum of jet cooled SiCN.

We have generated SiCN in a supersonic free expansion, and measured the laser induced fluorescence (LIF) spectrum. Prior to the experiments, ab initio calculations were carried out to obtain the information necessary for searching for the LIF signals. In addition to the X̃ 2Π state, the optimized structures of three excited states, 2Δ, 2Σ+, and 2Σ-, have been obtained. Guided by the predictions, the LIF excitation spectrum of SiCN was observed in the UV region. The rotational structure of the 000 band with the origin, 29 261.639 cm-1, indicated that the electronic transition is à 2Δ-X̃ 2Π. The spin-orbit (SO) constants of the X̃ 2Π and à 2Δ states were determined to be 140.824 and 4.944 cm-1, respectively. In the à 2Δ state, the Fermi resonance between the (0, 20, 0) 2Δ and (0, 00, 1) 2Δ vibronic levels was identified. The molecular constants of the X̃ 2Π state were determined through the simultaneous analysis of the combination differences derived from the present LIF data with the previously reported rotational transitions. The spectroscopic parameters of the à 2Δ state were also obtained from the analysis where the constants of the X̃ 2Π state, derived above, were fixed at those values.

Infrared radiative decay dynamics from the γ 1u ((3)P2), H 1u ((3)P1), and 1u ((1)D2) ion-pair states of I2 observed by a perturbation facilitated optical-optical double resonance technique.

We report the spectroscopic and temporal analyses on the amplified spontaneous emission (ASE) from the single rovibrational levels of the Ω = 1u ion-pair series, γ 1u ((3)P2), H 1u ((3)P1), and 1u ((1)D2), of I2 by using a perturbation facilitated optical-optical double resonance technique through the c (1)Πg ∼ B (3)Π(0u (+)) hyperfine mixed valence state as the intermediate state. The ASE detected in the infrared region was assigned to the parallel transitions from the Ω = 1u ion-pair states down to the nearby Ω = 1g ion-pair states. The subsequent ultraviolet (UV) fluorescence from the Ω = 1g states was also observed and the relative vibrational populations in the Ω = 1g states were derived through the Franck-Condon simulation of the intensity pattern of the vibrational progression. In the temporal profiles of the UV fluorescence, an obvious delay in the onset of the fluorescence was recognized after the excitation laser pulse. These results revealed that ASE is a dominant energy relaxation process between the Ω = 1u and 1g ion-pair states of I2. Finally, the lifetimes of the relevant ion-pair states were evaluated by temporal analyses of the UV fluorescence. The propensity was found which was the longer lifetime in the upper level of the ASE transitions tends to give intense ASE.

High-resolution laser spectroscopy and magnetic effect of the B̃(2)E(')←X̃(2)A2(') transition of the (15)N substituted nitrate radical.

Rotationally resolved high-resolution fluorescence excitation spectra of the 0-0 band of the B̃(2)E(')←X̃(2)A2(') transition of the (15)N substituted nitrate radical were observed for the first time, by crossing a jet-cooled molecular beam and a single-mode dye laser beam at right angles. Several thousand rotational lines were detected in the 15 080-15 103 cm(-1) region. We observed the Zeeman splitting of intense lines up to 360 G in order to obtain secure rotational assignment. Two, nine, and seven rotational line pairs with 0.0248 cm(-1) spacing were assigned to the transitions from the X̃(2)A2(') (υ″ = 0, k″ = 0, N″ = 1, J″ = 0.5 and 1.5) to the (2)E3/2(') (J' = 1.5), (2)E1/2(') (J' = 0.5), and (2)E1/2(') (J' = 1.5) levels, respectively, based on the ground state combination differences and the Zeeman splitting patterns. The observed spectrum was complicated due to the vibronic coupling between the bright B̃(2)E(') (υ = 0) state and surrounding dark vibronic states. Some series of rotational lines other than those from the X̃(2)A2(') (J = 0.5 and 1.5) levels were also assigned by the ground state combination differences and the observed Zeeman splitting. The rotational branch structures were identified, and the molecular constants of the B̃(2)E1/2(') (υ = 0) state were estimated by a deperturbed analysis to be T0 = 15 098.20(4) cm(-1), B = 0.4282(7) cm(-1), and DJ = 4 × 10(-4) cm(-1). In the observed region, both the (2)E1/2(') and (2)E3/2(') spin-orbit components were identified, and the spin-orbit interaction constant of the B̃(2)E(') (υ = 0) state was estimated to be -12 cm(-1) as the lower limit.

High-resolution laser spectroscopy and magnetic effect of the B̃2E' ← X̃2A2' transition of 14NO3 radical.

Rotationally resolved high-resolution fluorescence excitation spectra of (14)NO3 radical have been observed for the 662 nm band, which is assigned as the 0-0 band of the B̃(2)E' ←X̃(2)A2' transition, by crossing a single-mode laser beam perpendicularly to a collimated molecular beam. More than 3000 rotational lines were detected in 15,070-15,145 cm(-1) region, but it is difficult to find the rotational line series. Remarkable rotational line pairs, whose interval is about 0.0246 cm(-1), were found in the observed spectrum. This interval is the same amount with the spin-rotation splitting of the X̃(2)A2' (υ = 0, k = 0, N = 1) level. From this interval and the observed Zeeman splitting up to 360 G, seven line pairs were assigned as the transitions to the (2)E'(3/2) (J' = 1.5) levels and 15 line pairs were assigned as the transitions to the (2)E'(1/2) (J' = 0.5) levels. From the rotational analysis, we recognized that the (2)E' state splits into (2)E'(3/2) and (2)E'(1/2) by the spin-orbit interaction and the effective spin-orbit interaction constant was roughly estimated as -21 cm(-1). From the number of the rotational line pairs, we concluded that the complicated rotational structure of this 662 nm band of (14)NO3 mainly owes to the vibronic interaction between the B̃(2)E' state and the dark Ã(2)E″ state through the a2″ symmetry vibrational mode.

Vibrationally hot bands of the SiCN à 2Δ - X̃ 2Π system.

We have generated SiCN in supersonic free jet expansions and observed the laser induced fluorescence (LIF) spectrum. In addition to the vibronic bands from the vibrationless level of the X̃ (2)Π state, the hot bands from the bending vibrational level, à (01(1)0) (2)Φ - X̃ (01(1)0) (2)Δ and à (01(1)0) (2)Π - X̃ (01(1)0) (2)Σ((-)), have been measured. The rotational energy levels were reasonably analyzed as those of the (2)K' - (2)K″ transitions, but their line intensities calculated from the Hönl-London factors derived in the intermediate case between Hund's case (a) and (b) could not reproduce the observed spectra. The Hönl-London factors derived in the (2)Λ' - (2)Λ″ ((2)Δ - (2)Π) transition reasonably reproduced the spectra. It indicates that coupling between the electronic orbital and vibrational angular momenta is weak in the SiCN (2)Δ - (2)Π system, and a basis set of |Λ v2 l Σ;J P MJ>, the so-called "l-basis", better describes the system than that of |Λ v2 K Σ;J P MJ>.

FTIR spectroscopy of NO3: perturbation analysis of the ν3+ν4 state.

High-resolution Fourier transform infrared spectra of the 15NO3 ν3+ν4 and ν3+ν4-ν4 bands were observed in the 1472 and 1112 cm(-1) regions. Compared with the case of 14N species, large effects of perturbations were recognized in many rotational levels of the 15NO3 ν3+ν4 state, and it was found that the ν2+2ν4 state is responsible for the perturbation. Although a direct Coriolis interaction (Δν2 = 1, Δν3(or Δν4)=1) is not present between these two vibrational levels, anharmonic terms including Φ344 and Φ444 mix ν3+ν4 and 3ν4, ν2+2ν4, and ν2+2ν4 mixes with ν2+ν4 to produce Coriolis interaction between ν3+ν4 and ν2+2ν4. An analysis gave the energy difference of 7.274 cm(-1) between two levels, and interaction parameters were determined. Similar perturbation analysis was applied for the 14N species, and the previous (p)P(N,K) assignment of the ν3+ν4 A'-ν4 E' band was changed for giving one A2' state. Spectral lines to another A1' state were not assigned because of weak intensity, which is explained by intensity anomaly through vibronic interaction, reflecting the transition moment of the B2E'-X2A2' electronic band.