Nonstationary spectroscopy of the 1–2.5 THz frequency band with the use of solid-state devices

We develop the principles of construction of a gas spectrometer based on nonstationary effects (freely decaying polarization, fast sweep, etc.) with the use of solid-state devices in the terahertz frequency band. A spectrometer based on quantum semiconductor superlattices (QSSLs), which is operated at up to 2.5 THz and meets the requirements of high and ultra-high resolution spectroscopy is implemented. As the radiation source in this spectrometer, we use a frequency synthesizer which was developed by the authors of this paper. The device is based on a phase-shift keyed Gunn oscillator and a QSSL frequency multiplier. As the receiving system, a QSSL mixer operated in harmonic mode was employed. The possibilities of harmonic generation by using the radiation of a spectrally pure Gunn oscillator and a QSSL frequency multiplier are studied with the help of the IR Fourier spectrometer “BOMEM” DA3.002 with Si-composite bolometer operated at a temperature of 4.2 K. The 45th harmonic at a frequency of about 6.5 THz was reached in the experiment. The spectral absorption lines of NH3 and CO at 2400017.632 and 1841345.506 MHz, respectively, were measured.     

Laser stark spectroscopy of the ν2 fundamental band of 15NH3

The ν₂ fundamental band of ¹⁵NH₃ has been observed with a laser Stark spectrometer in Doppler-limited resolution. A set of 38 band constants including the electric dipole moment and its rotational dependence are determined from 416 Stark resonances observed in the present work and three submillimeter lines reported in the literature. The ν₂-band absorption line frequencies in the region 800–1160 cm⁻¹ and their relative absorption intensities are estimated from the band constants.     

Stark modulation infrared diode laser spectroscopy of the ν6 + ν8 band of diacetylene

The infrared diode laser spectrum of the ν₆ + ν₈ band of diacetylene (HCCCCH), i.e., a combination band of symmetric π_g (ν₆) and antisymmetric π_u (ν₈) CCH bending vibrations, was recorded by the Stark and source modulation techniques. The analysis of the Stark modulation spectrum allowed us to locate the 2ν₆ (Σ_g⁺) and 2ν₈ (Σ_g⁺) vibrational states, which are inaccessible by infrared transitions from the ground state. It is also shown that the Stark modulation spectrum can be used to confirm the rotational assignment of the ν₆ + ν₈ band.     

CO2 pressure broadening and shift coefficients for the 1–0 band of HCl and DCl

CO₂ broadened spectra of the 1–0 band of H³⁵Cl and H³⁷Cl, observed near 2886 cm^?1, and the 1–0 band of D³⁵Cl and D³⁷Cl, located near 2089 cm^?1, have been recorded at room temperature and five total pressures between 150 and 700 Torr, using a Bruker IFS125HR Fourier transform spectrometer. Spectra of pure HCl were also recorded. CO₂ broadening and shift coefficients of HCl and DCl have been measured using multi-spectrum non-linear least squares fitting of Voigt profiles. The analysis of the 1–0 band of DCl was complicated by the presence of overlapping CO₂ bands, which were included in the treatment as absorption coefficients calculated taking line-mixing effects into account.     

High-resolution inverse Raman spectroscopy of the ν1 band of water vapor

The Raman spectrum of the ν₁ band of water vapor at 7 Torr and 296 K, and at 84 Torr and 404 K, has been measured using high-resolution inverse Raman spectroscopy. The frequencies and relative intensities of the observed transitions are compared to a spectral model based on infrared data. Self-broadening coefficients have been determined for 22 lines from J = 0 to J = 8.     

High-resolution spectroscopy of the v2 = 2 a ← v2 = 1 s band of 14NH3

Twenty-one transitions of the v₂ = 2 a ← v₂ = 1 s hot band of ¹⁴NH₃ have been observed by an infrared microwave sideband laser spectrometer with an absolute accuracy of 0.00002 cm⁻¹. One hundred and seventeen transitions of the band have been obtained by a Fourier transform infrared spectrometer at a resolution of 0.005 cm⁻¹. A weighted least-squares analysis of these data has been carried out to yield 17 molecular parameters for the v₂ = 2 a state. These parameters reproduce the experimental frequencies with a root mean square deviation of 0.000123 cm⁻¹. To calculate the frequencies to this accuracy it was necessary to take into account the Δ(K − l) = ±3 interaction between the v₂ = 2 a and v₄ = 1 a states.     

Sub-Doppler laser-Stark and high-resolution Fourier transform spectroscopy of the ν3 band of formic acid

The 5.6-μm band of HCOOH, which is the strong carbonyl stretch mode, is analyzed using a combination of sub-Doppler resolution laser-Stark data obtained with a CO laser and Fourier transform data obtained from a Bomem interferometer. The Fourier transform data, including 647 lines with J′ ≤ 22 and K_a ≤ 11, are fit with a Watson-type Hamiltonian to determine excited state constants. The Coriolis interactions with v₅₊₉ and v₆₊₉, previously noted by Kuze et al., are included in the analysis; the former by using an exact diagonalization technique, the latter via perturbation theory. Taking the molecular parameters from this fit, the laser-Stark data are then analyzed to give ground and excited state dipole moments, yielding the following results in Debyes: μ″_a=1.4071(8)μ″_b=0.227(10)μ′_a=1.4353(9)μ′_b=0.214(9), where the errors are 3σ estimates. The laser-Stark data are limited to J′ ≤ 7 and give a ± 14 MHz fit to 191 lines.     

High-resolution spectroscopy of the v2 = 2 a ← v2 = 1 s band of 15NH3

Twenty-four transitions of the v₂ = 2 a ← v₂ = 1 s hot band of ¹⁵NH₃ have been observed by an infrared microwave sideband laser spectrometer. In addition, 149 transitions of the band have been obtained by a Fourier transform spectrometer at a resolution of 0.02 cm⁻¹. A weighted least-squares analysis has been carried out and the rms deviation of the fit is 0.00097 cm⁻¹. It was necessary to include the Δ(K − l) = ±3 interaction between the v₂ = 2 a and the v₄ = a states in the analysis.     

Electronic structure of bis(benzo)pentathienoacene in gas and solid phase: ultraviolet photoemission spectroscopy and energy band calculation

Ultraviolet photoemission spectroscopic measurements of bis (benzo)pentathienoacene were carried out in gas and solid phase. For the measurements of solid phase, vacuum deposited films in both amorphous and crystalline phase were prepared on different substrates of HOPG and polycrystalline Au, respectively. The adiabatic ionization energies were determined to be 6.8₄, 5.3₂, and 5.0₈ eV, for gas, amorphous, and crystalline phases, respectively. The spectral lineshapes were interpreted with the aid of the density functional calculations for both isolated molecule and single-crystal structure. The calculated electronic structures were further analyzed in terms of the energy band dispersion and the transport properties of charge carriers.     

Measurement of the wavelength modulation indices with selective reflection spectroscopy

The wavelength modulation indices are measured based on harmonic amplitude ratio of 4famp/6famp (4famp and 6famp are the 4- and 6-th harmonic central peak amplitudes correspondingly) with the Doppler-free selective reflection modulation spectroscopy. The experiments for the 6S1/2(F = 4) → 6P3/2(F' = 5) transition of cesium D2 line with 30-MHz linewidth were carried out. The 4f- and 6f-harmonic signals were detected with two digital lock-in amplifiers separately. The maximum error for modulation indices measurement was ±0.1 within the range of m from 3 to 6. The non-linear modulation behaviour of an external cavity diode laser induced by voltage tuning was studied with this method. The method for modulation indices measurement does not require a solid etalon as usual for measuring the wavelength modulation depth and the absorption linewidth correspondingly.     

Incoherent broad-band cavity-enhanced absorption spectroscopy for simultaneous trace measurements of NO2 and NO3 with a LED source

In the past decade, due to a growing awareness of the importance of air quality and air pollution control, many diagnostic tools and techniques have been developed to detect and quantify the concentration of pollutants such as NO _x , SO _x , CO, and CO₂. We present here an Incoherent Broad-Band Cavity-Enhanced Spectroscopy (IBB-CEAS) set-up which uses a LED emitting around 625 nm for the simultaneous detection of NO₂ and NO₃. The LED light transmitted through a high-finesse optical cavity filled with a gas sample is detected by a low resolution spectrometer. After calibration of the spectrometer with a NO₂ reference sample, a linear multicomponent fit analysis of the absorption spectra allows for simultaneous measurements of NO₂ and NO₃ concentrations in a flow of ambient air. The optimal averaging time is found to be on the order of 400 s and appears to be limited by the drift of the spectrometer. At this averaging time the smallest detectable absorption is 2×10⁻¹⁰ cm⁻¹, which corresponds to detection limits of 600 pptv for NO₂ and 2 pptv for NO₃. This compact and low cost instrument is a promising diagnostic tool for air quality control in urban environments.     

Analysis of optical properties of bio-smoke materials in the 0.25–14 μm band

At present, research into optical properties of bio-smoke materials mostly concentrates on single band or single germplasm. Herein, we measured the spectral reflectance of three eukaryotic bio-smoke materials and three prokaryotic bio-smoke materials in the waveband from 0.25 μm to 14μm. Based on the Kramers-Kroning algorithm, the complex refractive index m(λ) was calculated and the Fourier-transform infrared(FTIR) spectra of materials were analyzed. The results show that n(λ) of bio-smoke materials varies between 1.1-2, and n(λ) values in the visible light to near-infrared wavebands are significantly larger than those in other wavebands. The k(λ) of bio-smoke materials varies between 0-0.4.At 6-6.5 μm, k(λ) of prokaryotic materials is 3 times that of eukaryotic materials, which is caused by C=O stretching vibration of amide I and C-N stretching vibration of amide Ⅱ in proteins. At 2.5-3 μm and 9.75 μm, k(λ) values of eukaryotic bio-smoke materials are nearly 2 times that of prokaryotic ones. The absorption peak at 2.5-3 μm is mainly triggered by C-H stretching vibration in lipid and O-H stretching vibration in bound water. The absorption peak at 9.75 μm is mainly caused by symmetric stretching vibration of PO2-in nucleic acids.     

Laser Stark spectroscopy; a case study in the ν2 fundamental band of 14NH3

The ν₂ fundamental band of ¹⁴NH₃ is observed with a laser Stark spectrometer in Doppler-limited resolution. A set of 41 constants including the electric dipole moment and its rotational dependence are determined from 360 Stark resonances observed in the present work and 67 millimeter- and submillimeter-wave inversion and rotation-inversion lines reported in the literature. The rms residual of the fit is 3.1 × 10⁻⁴ cm⁻¹. Field-free transition frequencies of the band in the region 800–1160 cm⁻¹ are calculated from the constants and tabulated together with their estimated uncertainties and relative absorption intensities. Rotational dependence of the electric dipole matrix elements of a C_3v molecule is presented on the basis of the conventional theory of vibration-rotation.     

Spin splittings in the ν3 band of NO2

Spin splittings for several important atmospheric lines in the ν₃ band of NO₂ have been measured by diode laser. An improved spin-splitting program has been developed which takes into account the asymmetry effects in the lower K_a splittings. The measured spin splittings and the derived spin-rotational constants are reported in this study to a much higher accuracy than previously achieved.     

Angle-resolved photoemission of chain-like molecules: the electronic band structure of sexithiophene and sexiphenyl

Here we report the electronic π-band structure of sexithiophene obtained from 6T(010) oriented films. The angle-resolved valence band photoemission results taken parallel and perpendicular to the molecular axis are compared to those of sexiphenyl and interpreted in terms of intra- and inter-molecular band dispersion. We show that the strong photoemission intensity variations with emission angle parallel to the molecular axis are well reproduced by the Fourier transforms of the molecular orbitals of the isolated molecules. These results imply that ARUPS can yield quite detailed information about molecular geometry, both in terms of molecular orientation and internal structure.     

Laser spectroscopy of sulfur dioxide: The ν1 band of 32S16O18O and the ν3 band of 32S18O2

The combination of data obtained from infrared-microwave double resonance with those from pure rotational spectroscopy has allowed a full set of constants for the ν₁ band of S¹⁶O¹⁸O to be determined. Tunable diode laser spectroscopy has been carried out on the ν₃ band of S¹⁸O₂ and 112 transitions were measured with a nominal accuracy of ±0.001 cm⁻¹. Band constants have been determined from these data.     

Infrared laser velocity modulation spectrum of the ν3 fundamental band of HBCI+

The infrared spectrum of the ν₃ fundamental band of HBC1⁺ has been observed using the velocity modulation detection technique. The ion was produced in an ac glow discharge containing a mixture of H₂ and BC1₃. Thirty-two transitions of the fundamental band of the most naturally abundant isotopomer, H¹¹B³⁵C1⁺, between 1105 and 1170cm^?1 have been assigned. The ν₃ band origin and rotational constants have been determined to be ν₀ = 1121.5677(20)cm^?1, B ₀ = 0.63089(23)cm^?1 and B ₁ = 0.62699(21)cm^?1. A second series of lines have been attributed to the H¹¹B³⁷C1⁺ isotopomer, although it has not been possible to make an unambiguous J assignment of these lines.     

Tunneling of Charged and Magnetized Fermions from the Kerr-Newman-Ads Black Hole with Magnetic Charges

Tunneling of charged and magnetized Dirac particles from the Kerr-Newman-Ads black hole with magnetic charges is discussed in this paper. Owing to the electric and magnetic fields would couple with gravity field, we introduce the Dirac equation of charged and magnetized particles. Then by redefining the equivalent charge and gauge potential corresponding to the source with electric and magnetic charges, we discuss this tunneling once and obtain the same Hawking temperature. Both results show that the fermions tunneling formalism also come into existence in the charged and magnetized background space time.     

Tunneling of Charged and Magnetized Fermions from the Reissner-Nordström Black Hole with Magnetic Charges

The Kerner-Mann fermions tunneling framework is extended to the spin particles with electric and magnetic charges in this paper. We rewrite the electromagnetic field tensor and the Lagrangian of the field corresponding to the source with electric and magnetic charges to redefine an equivalent charge. We only consider the case that the ratio of the electric charge and magnetic charge of the emission is constant and equal to the source. The result shows that when the energy conservation together with the electric charge and magnetic charge conservations are taken into account in the dynamical background space time, the emission rate agrees with the underlying unitary theory and the actual radiation spectrum of charged and magnetized fermions also derivates from the pure thermal one.