Absorption Spectrum Of Water Vapor Research Articles

Laser Absorption Spectroscopy of H<sub>2</sub>O in the 12 252-12 312 cm<sup>-1R</sup>egion Using Herriott-Type Cell

We study the absorption spectra of water vapor by the 899-29 Ti:sapphire laser in the region between 12 252-12 312 cm-1. Due to the weak absorption of H2O, a folded multi-pass optical path cell of Herriott-type is used to increase the sensitivity of detection. Totally, forty-three lines with intensity ranging around 10-24cm-1/molecule are recorded and the centre frequency of transitions is derived by fitting observed lines using Voigt profile.

초소형의 광섬유 결합형 테라헤르츠 모듈을 이용한 시간영역에서의 분광 및 이미징

본 논문에서는 초소형의 광섬유 결합형 테라헤르츠 모듈을 이용하여 테라헤르츠 시간영역 분광 및 영상 시스템을 구성하였다. 구성된 THz 분광 시스템을 이용하여 3 THz 이상의 자유공간에 분포되어 있는 수분의 고유 흡수 스펙트럼을 관측하였고 테라헤르츠 대역에서의 Si, <TEX>$Al_2O_3$</TEX>, GaAs기판에 대한 굴절률을 측정하였으며 측정을 위해 다중 반사를 고려한 전달 함수를 이용한 굴절률 측정 방법을 이용하였다. 또한, 테라헤르츠 영상 시스템을 이용하여 의료용 칼과 클립을 측정하여 250 <TEX>${\mu}m$</TEX> 간격으로 <TEX>$192{\times}89$</TEX> 픽셀의 영상을 얻었다. We have demonstrated a terahertz (THz) time-domain spectroscopy and imaging system using compact fiber-coupled THz modules. Using this THz spectroscopy system we have measured the absorption spectrum of water vapor in free space over 3 THz, as well as the refractive indices of various substrates such as Si, <TEX>$Al_2O_3$</TEX>, and GaAs using the transfer-function method. Through the THz imaging system we have observed a high-quality THz image of a medical knife and metal clip sample, with a resolution of <TEX>$192{\times}89$</TEX> pixels using a step size of 250 <TEX>${\mu}m$</TEX>.

Water dimer equilibrium constant calculation: A quantum formulation including metastable states

We present a full quantum evaluation of the water second virial coefficient B(T) based on the Takahashi-Imada second order approximation. As the associated trace T r[e(-βH(AB)) - e(-βH(0)(AB))] is performed in the coordinate representation, it does also include contribution from the whole continuum, i.e., resonances and collision pairs of monomers. This approach is compared to a Path Integral Monte Carlo evaluation of this coefficient by Schenter [J. Chem. Phys. 117, 6573 (2002)] for the TIP4P potential and shown to give extremely close results in the low temperature range (250-450 K) reported. Using a recent ab initio flexible potential for the water dimer, this new formulation leads to very good agreement with experimental values over the whole range of temperatures available. The virial coefficient is then used in the well known relation Kp(T) = -(B(T) - bM)/RT where the excluded volume bM is assimilated to the second virial coefficient of pure water monomer vapor and approximated from the inner repulsive part of the interaction potential. This definition, which renders bM temperature dependent, allows us to retrieve the 38 cm(3) mol(-1) value commonly used, at room temperature. The resulting values for Kp(T) are in agreement with available experimental data obtained from infrared absorption spectra of water vapor.

Accounting for humidity of exhaled air for retrieving gaseous biomarkers

In this work, we use numerical simulation to estimate errors of the differential-absorption retrieval of concentrations of such gaseous biomarkers as CH4, CO, NH3, N2O, C2H6, and H2S from the absorption spectra of a three-component gas mixture in the 2–4 μm spectral region. The gas mixture is supposed to simulate exhaled air. The absorption spectra were calculated with a resolution of 2 cm−1 using the HITRAN database. The influence of subtraction of the water vapor absorption spectrum from the simulated spectrum on the retrieval error is studied. The water vapor concentration in the mixture in calculations of its contribution to the spectrum was determined from the absorption measured at 3800 cm−1.

An improved line list for water vapor in the 1.5 µm transparency window by highly sensitive CRDS between 5852 and 6607 cm−1

The absorption spectrum of water vapor in “natural” isotopic abundance has been recorded by high sensitivity Continuous Wave Cavity Ring Down Spectroscopy (CW-CRDS) between 5852 and 6607cm−1. The investigated region covers the 1.5µm transparency window of major importance for atmospheric applications. The achieved sensitivity of the recordings varies from αmin ∼2×10−11 to 2×10−10cm−1 and allows for a significant amount of new or more accurate observations compared to previous studies. Measured line intensities cover a range of six orders of magnitude (2×10−30−2×10−24cm/molecule at room temperature). The vibration–rotation assignments were performed using known experimental energy levels and calculated spectra based on variational calculations by Schwenke and Partridge.Five thousand seven hundred and twenty seven lines were assigned to 6379 transitions of six water isotopologues (H216O, H218O, H217O, HD16O, HD18O and HD17O). The first detection of lines due to HD17O in “natural” water (relative abundance on the order of 1.1×10−7) illustrates the sensitivity of the recordings. Most of the 1842 newly reported transitions belong to the main isotopologue (1022 transitions) and to the HD16O isotopologue (684 transitions). Sixty-three levels are newly determined and 22 are corrected by more than 0.015cm−1 compared to those recommended by the water IUPAC task group.Overall, a list of 6589 transitions was constructed for the studied region. The present CRDS line list complemented with 210 strong transitions from the literature is believed to be the most complete empirical list of the region. The obtained results are critically compared to recent IUPAC task group compilations. Overall the agreement between variational and measured intensities is very satisfactory. We nevertheless point out a number of important disagreements for some lines of the highly excited bending bands, mainly 4ν2 of H216O.

CRDS of water vapor at 0.1 Torr between 6886 and 7406 cm−1

The absorption spectrum of water vapor in “natural” isotopic abundance has been recorded by high sensitivity CW-Cavity Ring Down Spectroscopy (CW-CRDS) between 6885.79 and 7405.91cm−1. This strong absorbing region includes the first hexad of interacting vibrational bands which was previously studied by Fourier Transform Spectroscopy. The achieved sensitivity of the recordings varies from αmin∼2×10–11 to 2×10−10cm−1 allowing us to use a sample pressure of 0.1Torr, making pressure broadening of the line profile mostly negligible. Weak lines in the vicinity of much stronger lines could then be accurately measured. The weakest lines have intensity on the order of 5×10–28cm/molecule at 296K. A set of 4471 lines were assigned to 4916 transitions of five water isotopologues (H216O, H218O, H217O, HD16O and HD18O). A small number of new energy levels was determined mostly for the H217O isotopologue. The previous investigations and existing databases are critically evaluated. In particular, a number of corrections and new assignments are proposed for the water list provided by the HITRAN database in the considered region. As a result, a complete list of 12,700 transitions for water in “natural” isotopic abundance is provided as Supplementary Material for the 6885–7408cm−1 region.

Intracavity sensing via compliance voltage in an external cavity quantum cascade laser

We demonstrate a technique for gas phase spectroscopy and sensing by detecting changes in compliance voltage of an external cavity quantum cascade laser due to intracavity absorption. The technique is characterized and used to measure the absorption spectrum of water vapor and Freon-134a.

High resolution Fourier transform spectroscopy of HD16O: Line positions, absolute intensities and self broadening coefficients in the 8800–11,600 cm−1 spectral region

High-resolution water vapor absorption spectra have been measured at room temperature in the 8800–11,600cm−1 spectral region. They were obtained using the mobile BRUKER IFS 120M Fourier transform spectrometer (FTS) from ULB-SCQP coupled to the 50m base long multiple reflection White type cell in GSMA laboratory. The absorption path was 600m and different H2O/HDO/D2O mixtures were used. Measurements of line positions, intensities and self-broadening coefficients were performed for the HD16O isotopologue. 6464 rovibrational assignment of the observed lines was made on the basis of global variational predictions and allowed the identification of new energy levels. 3ν3, 2ν1+ν3, 3ν1+ν2, ν1+2ν3 and 2ν2+2ν3 are the five strongest bands. The present paper provides a complementary data set on water vapor for atmospheric and astrophysical applications.

Absorption spectrum of deuterated water vapor enriched by 18O between 6000 and 9200 cm−1

The absorption spectrum of water vapor enriched by deuterium and oxygen-18 is analyzed in the 6000–9200cm−1 region. The spectrum has been recorded at room temperature with a Bruker IFS 120h Fourier transform spectrometer. More than 14,000 absorption lines were measured in the recorded spectrum. The vibration–rotation assignments were performed on the basis of previously published experimental energies and of variational calculations. Nine water species (H216O, HD16O, D216O, H218O, HD18O, D218O, H217O, HD17O and D217O) were found to contribute to the observed absorption. More than 3600 lines of 19 vibrational bands of D218O and about 4700 lines of 16 bands of HD18O with J as high as 19 and Ka as high as 11 were assigned. The main part of the HD18O and D218O lines and all lines of HD17O and D217O were observed in the laboratory for the first time. The obtained vibration–rotation energy levels are compared with previous experimental studies and the results of variational calculations.

E132 12パス半導体レーザ光吸収を用いた2次元温度・濃度計測技術(OS-18: 熱・物質移動の計測および現象解析(3))

Exhaust gas temperature is an important factor in NO_x, THC and PM emissions of engines. Especially 2D temperature and concentration distribution plays an important role for the engine efficiency. A thermocouple is intrinsically a point temperature measurement method and noncontact 2D temperature distribution cannot be attained by thermocouples. In this study, the experimental research has been conducted in order to develop the noncontact and fast response 2D temperature and concentration distribution measurement method. The method is based on a computed tomography(CT) method using absorption spectra of water vapor at 1388nm. It has been demonstrated that the method has been successfully applied to engine exhausts to measure 2D temperature distributions using the 12-path measurement cell.

The absorption spectrum of water in the 1.25 μm transparency window (7408–7920 cm −1)

The absorption spectrum of water vapor in “natural” isotopic abundance has been recorded between 7408 and 7920 cm −1 by high sensitivity cw-cavity ring down spectroscopy (CW-CRDS). This region covers the low energy part of the 1.25 μm transparency window and corresponds to weak water absorption of the first hexad of interacting vibrational bands. The achieved sensitivity – on the order of α min ∼ 2 × 10 −10 cm −1 – has allowed one to newly measure 2028 weak transitions with intensities down to 2 × 10 −29 cm/molecule at 296 K i.e. more than two orders of magnitude lower than previous observations. Three hundred and fourty-one new and corrected energy levels belonging to 26 vibrational states of H 2 16O, H 2 18O, H 2 17O, and HD 16O could be determined from the vibration–rotation analysis based on variational calculations by Schwenke and Partridge. The previous investigations in the studied region by Fourier Transform Spectroscopy and existing databases have been critically evaluated. The most complete list for water in the region is provided as Supplementary Material.

PCF-Based Cavity Enhanced Spectroscopic Sensors for Simultaneous Multicomponent Trace Gas Analysis

A multiwavelength, multicomponent CRDS gas sensor operating on the basis of a compact photonic crystal fibre supercontinuum light source has been constructed. It features a simple design encompassing one radiation source, one cavity and one detection unit (a spectrograph with a fitted ICCD camera) that are common for all wavelengths. Multicomponent detection capability of the device is demonstrated by simultaneous measurements of the absorption spectra of molecular oxygen (spin-forbidden b-X branch) and water vapor (polyads 4v, 4v + δ) in ambient atmospheric air. Issues related to multimodal cavity excitation, as well as to obtaining the best signal-to-noise ratio are discussed together with methods for their practical resolution based on operating the cavity in a “quasi continuum” mode and setting long camera gate widths, respectively. A comprehensive review of multiwavelength CRDS techniques is also given.

The absorption spectrum of water between 13 540 and 14 070 cm −1: ICLAS detection of weak lines and a complete line list

The absorption spectrum of water vapor has been investigated by Intracavity Laser Absorption Spectroscopy (ICLAS) between 13 540 and 14 070 cm −1. This spectrum is dominated by relatively strong transitions of the 4 δ polyad of vibrational states. The achieved sensitivity – on the order of α min ∼ 10 −9 cm −1 – has allowed one to newly measure 222 very weak transitions with intensities down to 5 × 10 −28 cm/molecule at 296 K. Fifty new or corrected H 2 16O energy levels belonging to a total of 13 vibrational states could be determined from the rovibrational analysis based on variational calculations by Schwenke and Partridge. The previous investigations in the region by Fourier Transform Spectroscopy were critically evaluated and used to construct the best to date set of energy levels accessed by transitions in the considered region. All the rovibrational transitions reaching these upper energy levels and having intensities larger than 4.0 × 10 −28 cm/mol were calculated. In the resulting line list, the positions at the level of experimental accuracy were augmented with variational intensities leading to the most complete line list for water in normal isotopic abundance in the 13 500–14 100 cm −1 region.

In situ absorption sensor for NO in combustion gases with a 5.2 μm quantum-cascade laser

A new mid-infrared absorption sensor for in situ detection of nitric oxide in combustion exhaust gases has been developed and demonstrated for temperatures up to 700K. A novel external-cavity quantum-cascade diode laser, which can be wavelength-tuned over the R-branch of the fundamental absorption band near 5.2μm, was utilized, enabling critical evaluation of the interference absorption by H2O in combustion exhaust gases. The water vapor absorption spectrum was measured over the range 1880cm−1 to 1951cm−1 at 633K (680F), typical of conditions in the economizer region of coal-fired power plants. Based on the data for water vapor interference and laser performance, four candidate fundamental-band transitions (R10.5 (1/2, 3/2) and R15.5 (1/2, 3/2)) were selected as optimum and subsequently investigated in detail. A laboratory combustion exhaust rig with a 1.79m constant-temperature line-of-sight path was then used to validate the sensor for NO concentrations between 20 and 95ppm at 600K; an NO detection limit of <60ppbm(Hz)−1/2 was obtained. The sensor was subsequently applied in successful real-time measurements of NO across a 3m path in the exhaust of a pulverized-coal-fired power plant, including capture of a 30% transient change in NO concentration at the economizer exit that occurred during the shutdown and recovery of the SNCR NOx control system. The sensor shows excellent promise for monitoring NO in practical combustion exhausts of coal-fired power plants at temperatures up to at least 700K.

Off-axis integrated cavity output spectroscopy and its application

Based upon the property of optical cavity and the principle of signals and systems, the measural theory and signal expression of off-axis integrated cavity output spectroscopy (Off-axis ICOS) have been analyzed and deduced. A compact and low-cost Off-axis ICOS apparatus, which used a special circuit to integrate the cavity output signal, was then described and experimented. The absorption spectrum of water vapor in the spectral range of 6587∼6595.5 cm −1 was measured with this Off-axis ICOS system, and the measured spectral parameters were compared with the results of continuous-wave cavity ring down spectroscopy (CW-CRDS) and HITRAN2004 database. The detectable sensitivity of the system was achieved as ∼2.8 × 10 −9 cm −1.

Rapid-scanning terahertz precision spectrometer with more than 6 THz spectral coverage

We report a terahertz time-domain spectrometer with more than 6 THz spectral coverage and 1 GHz resolution based on high-speed asynchronous optical sampling. It operates at 2 kHz scan rate without mechanical delay stage. The frequency error of the system at 60 s acquisition time is determined by comparing a measured water vapor absorption spectrum to data reported in the HITRAN database. The mean error of 87 evaluated absorption lines is 142 MHz.

Intracavity spectroscopy of water vapor in the 1.06-micrometer range

Using an intracavity spectrometer with a neodymium glass laser with a spectral resolution of 0.035 cm−1 and threshold absorption sensitivity of 10−8 cm−1, water vapor absorption spectra have been studied. The H2O and HDO absorption spectra have been recorded in the temperature interval of 300–1000 K. The spectra have been identified, and many new energy levels of the H2O and HDO molecules have been determined. Coefficients of line center shifts induced by pressures of H2, O2, Ar, Xe, and Kr buffer gases and of the atmospheric air have been measured. For all buffer gases, a linear dependence of the shift magnitude on the pressure was observed. For a proper measurement of the coefficients of the line center shift, a technique employing a temperature-stabilized Fabry-Perot interferometer has been proposed.

Plasmon-resonant Microchip Emitters and Their Applications to Terahertz Spectroscopy

This paper reviews recent advances in emission of THz radiation from our original dual-grating gate high-electron mobility transistors (HEMT's) originated from two-dimensional plasmons. The dual grating gates can alternately modulate the 2D electron densities to periodi- cally distribute the plasmonic cavities along the channel, acting as an antenna. The sample was fabricated with standard GaAs-based heterostructure material systems, succeeding in emission of broadband (0.5 to 6.5THz) radiation even at room temperature from self-oscillating 2D plas- mons under appropreate DC-bias conditions. Currently maximum available THz output power is estimated to be on the order of 1 to 10W from a single die active area of 75 £ 75m 2 with an excellent power conversion e-ciency of 10 i3 . The fabricated device was introduced to the Fourier-transform infrared spectroscopy as a microchip THz source. Water-vapor absorption spectrum was successfully observed at 300K, which is proven to the standard data provided by NASA.

ICLAS of water in the 770 nm transparency window (12 746–13 558 cm −1). Comparison with current experimental and calculated databases

The absorption spectrum of water vapor has been investigated by intracavity laser spectroscopy (ICLAS) in the 12 746–13 558 cm −1 spectral region corresponding to an interesting transparency window of the atmosphere, partly obscured by the A band of molecular oxygen. The achieved sensitivity—in the order of α min∼10 −9 cm −1—has allowed one to measure 1062 water lines with intensities ranging from 1.6×10 −28 to 2.35×10 −24 cm/molecule at 296 K. A total of 169 new and improved energy levels belonging to 21 vibrational states could be determined from 374 newly measured transitions. The retrieved experimental line list is compared with the spectra calculated by Schwenke and Partridge, and Barber and Tennyson. Comparison with the available experimental databases shows that the obtained results represent a significant improvement of the knowledge of the water absorption in the considered region, in particular in the region of the oxygen A band.

Intracavity Absorption Spectroscopy of Atmospheric Water Vapor Using a Multimode Traveling-Wave Ring Dye Laser

The intracavity absorption spectra of water vapor in the atmosphere were observed in situ using a multimode unidirectional traveling-wave ring dye laser. Water vapor lines with absolute absorption coefficients of 10-7 to 10-9 cm-1 were measured with uncertainties of a few percents and their values were consistent with those in the HITRAN database within 10%. The sensitivity of the present apparatus was estimated to be 1 ×10-10 cm-1.