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.

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.

Far-infrared amplified spontaneous emission and collisional energy transfer between the E 0(g)⁺ (³P2) and D 0(u)⁺ (³P2) ion-pair states of I2.

We report direct observation of far-infrared amplified spontaneous emission from the E 0(g)⁺ ((3)P2) (v(E) = 0 - 3) ion-pair state of I2 by using an optical-optical double resonance technique with the B (3)Πu (0(u)⁺) (v(B) = 19) valence state as the intermediate state. The directional far-infrared emission detected in the wavelength range from 19 to 28 µm was assigned to the vibronic transitions from the E 0(g)⁺ ((3)P2) ion-pair state to the D 0(u)⁺ ((3)P2) ion-pair state. The subsequent UV fluorescence from the D 0(u)⁺ ((3)P2) state was also observed, which consists not only from the vibrational levels populated by the amplified spontaneous emission but also from those populated by collisional energy transfer. Analyses of the vibrational distribution in the D 0(u)⁺ ((3)P2) state revealed that the population transfer through the amplified spontaneous emission was dominant under our experimental conditions.

Far infrared stimulated emission from the ns and nf Rydberg states of NO.

We report directional far-infrared emission from the υ = 0 vibrational levels of the 9sσ, 10sσ, 11sσ, 9f, and 10f Rydberg states of NO in the gas phase. The emission around 28 and 19 µm from the 9f state was identified as the downward 9f → 8g and subsequent 8g → 7f cascade transitions, respectively. The emission around 38 and 40 µm from the 10f state was identified as the 10f → 9g and 10f → 9dσπ transition, respectively. Following the excitation of the 9sσ, 10sσ, and 11sσ states, the emission around 40, 60, and 83 µm was assigned as the 9sσ → 8pσ, 10sσ → 9pσ, and 11sσ → 10pσ transitions, respectively. In addition to these emission systems originated from the laser-prepared levels, we found the emission bands from the 8f, 9f, and 10f states which are located energetically above the 9sσ, 10sσ, and 11sσ states, respectively. This observation suggests that the upward 8f ← 9sσ, 9f ← 10sσ, and 10f ← 11sσ optical excitation occurs. Since the energy differences between nf and (n + 1)sσ states correspond to the wavelength longer than 100 µm, the absorption of blackbody radiation is supposed to be essential for these upward transitions.

Laser induced amplified spontaneous emission from the f 0(g)(+) (3P0) ion-pair state of I2.

Laser induced amplified spontaneous emission (ASE) from the f 0g (+) ((3)P0) (vf = 1-7) ion-pair state of I2 was directly observed using an optical-optical double resonance technique with the B 0u (+) (vB = 21) valence state as the intermediate state. The emission detected at ~1660 nm was assigned to transitions from the f 0g (+) state to the D 0u (+) ((3)P2) ion-pair state. The transitions observed in the dispersed IR emission spectra were found to be between vibrational levels having the same vibrational quantum numbers in both electronic states, vf = vD. This is due to the almost parallel nature of the potential energy functions of the f 0g (+) and D 0u (+) states, leading to almost unit values for the Franck-Condon factors for vf = vD. That the observed infrared emission is due to ASE is shown by the facts that it propagated in a limited range of solid angles, exhibited a clear threshold against the input-laser power, and had different polarization to that of laser induced fluorescence.

Antimicrobial effect of blue light using Porphyromonas gingivalis pigment.

The development of antibiotics cannot keep up with the speed of resistance acquired by microorganisms. Recently, the development of antimicrobial photodynamic therapy (aPDT) has been a necessary antimicrobial strategy against antibiotic resistance. Among the wide variety of bacteria found in the oral flora, Porphyromonas gingivalis (P. gingivalis) is one of the etiological agents of periodontal disease. aPDT has been studied for periodontal disease, but has risks of cytotoxicity to normal stained tissue. In this study, we performed aPDT using protoporphyrin IX (PpIX), an intracellular pigment of P. gingivalis, without an external photosensitizer. We confirmed singlet oxygen generation by PpIX in a blue-light irradiation intensity-dependent manner. We discovered that blue-light irradiation on P. gingivalis is potentially bactericidal. The sterilization mechanism seems to be oxidative DNA damage in bacterial cells. Although it is said that no resistant bacteria will emerge using aPDT, the conventional method relies on an added photosensitizer dye. PpIX in P. gingivalis is used in energy production, so aPDT applied to PpIX of P. gingivalis should limit the appearance of resistant bacteria. This approach not only has potential as an effective treatment for new periodontal diseases, but also offers potential antibacterial treatment for multiple drug resistant bacteria.

Microwave spectrum of the H2DO+ ion: inversion-rotation transitions and inversion splitting.

Inversion-rotation spectral lines of the monodeuterated hydronium ion, H(2)DO(+), have been observed by a source-modulation spectrometer in the millimeter- to submillimeter-wave region. The ion was generated by a hollow-cathode discharge in a gas mixture of H(2)O and D(2)O. Nine inversion-rotation lines were measured precisely for the lowest pair of inversion doublets in the frequency region from 210 to 720 GHz. The measured lines were analyzed to derive rotational constants in the inversion-doublet states and inversion splitting. The inversion splitting in the ground state was determined to be 1,215,866(410) MHz, that is, 40.5569(137) cm(-1), where the numbers in parentheses give probable uncertainties estimated from the Jacobian matrix of the assumed centrifugal distortion constants of the inversion-doublet states. The determined inversion splitting is off by -0.58 cm(-1) from the predicted value of 41.14 cm(-1) by Rayamaki et al. using high-order coupled cluster ab initio calculations [J. Chem. Phys. 118, 10929 (2003)], and by 0.039 cm(-1) from the observed value of 40.518(10) cm(-1) by Dong and Nesbitt using high-resolution jet-cooled infrared spectroscopy [J. Chem. Phys. 125, 144311 (2006)] beyond the quoted uncertainty. The most astronomically important transition 0(00)(-)-1(0)(+) for the ortho species was measured at 673,257.024(31) MHz, which could be used as a radioastronomical probe investigating interstellar chemistry of deuterium fractionation in space.

Electronic absorption spectrum of a nonlinear carbon chain: trans-C6H4+.

The 2Bg-X2Au transition of a nonlinear carbon chain trans-C6H4+, and trans-C6D4+, has been observed in the gas phase. The spectra were detected in the 580 nm region by direct absorption with a cavity ringdown technique through a supersonic planar discharge. Though the rotational structure is not resolved, the band profiles were analyzed using a "total spectral fitting" procedure using ground-state constants calculated by the CASSCF and CASPT2 methods. The molecular constants in the upper state could thus be determined.