Absorption Spectra Of H2O Research Articles

Reduced Density Matrix Formulation of Quantum Linear Response.

The prediction of spectral properties via linear response (LR) theory is an important tool in quantum chemistry for understanding photoinduced processes in molecular systems. With the advances of quantum computing, we recently adapted this method for near-term quantum hardware using a truncated active space approximation with orbital rotation, named quantum linear response (qLR). In an effort to reduce the classic cost of this hybrid approach, we here derive and implement a reduced density matrix (RDM) driven approach of qLR. This allows for the calculation of spectral properties of moderately sized molecules with much larger basis sets than so far possible. We report qLR results for benzene and R-methyloxirane with a cc-pVTZ basis set and study the effect of shot noise on the valence and oxygen K-edge absorption spectra of H2O in the cc-pVTZ basis.

A multi-laser hybrid absorption sensor for simultaneous measurement of NH3, NO, and temperature in denitrification flue gas

The real-time monitoring of NH3, NO, and flue gas temperatures is critical to controlling NOx emissions from coal-fired power plants, reducing ammonia slip, and realizing accurate ammonia injection. However, few previous studies have utilized laser absorption sensors to measure these three indicators simultaneously. In this paper, a multi-laser hybrid sensor is designed based on tunable diode laser absorption spectroscopy (TDLAS) for simultaneous measurement of NH3, NO, and flue gas temperature. The sensor uses a distributed feedback (DFB) laser to target the NH3 and the H2O lines, and a quantum cascade laser (QCL) is used to target the NO line. In the measurements of NH3 and NO using calibration-free wavelength-modulated spectroscopy (CF-WMS), we employ a method to obtain the laser wavelength response by fitting the demodulated signal of a standard gas. Additionally, temperature measurements are obtained using the time-division multiplexing (TDM) strategy and direct absorption spectroscopy (DAS) techniques with the help of the absorption spectrum of H2O. Under static conditions, the relative accuracy of NH3 and NO detected by the sensor is 4.2% and 2%, respectively, and the maximum relative standard deviation of temperature is 1.3%. When tested under flowing conditions, the sensor can accurately capture NH3, NO, and temperature changes. The relative accuracy of NH3 and NO is 4.7% and 2.2%, and the relative standard deviation of temperature is 0.9%. The sensor has great potential in optimizing denitrification processes in thermal power plants.

Measurements and calculations of CO2-broadening and shift coefficients of water vapor transitions in the 5150–5550 cm−1 spectral region

The high-resolution H2O absorption spectra induced by CO2 pressure have been recorded using a Bruker IFS 125 HR FTIR spectrometer at room temperature in the 5150–5550 cm–1 spectral region. A multispectrum fitting procedure has been applied to these spectra to recover the spectral line parameters using the speed-dependent Voigt profile. The water vapor line broadening and shift coefficients for lines of two vibrational bands ν2+ν3 and ν1+ν2 were obtained. An uncertainty of the broadening coefficients for the unblended H2O absorption lines was estimated to be 2–3%. The calculations of line-broadening and line-shifting parameters were performed using the semi-empirical method which is based on the impact theory and enables a realistic prediction modified by introducing additional parameters obtained by using empirical data. The root mean square deviations of measured and calculated line widths and shifts were 0.0086 and 0.0053 cm−1 atm−1, respectively.

Development of a broadband cavity-enhanced absorption spectrometer for simultaneous measurements of ambient NO3, NO2, and H2O

Abstract. We describe the characteristics and performances of our newly built broadband cavity-enhanced absorption spectrometer for measurements of nitrate radical (NO3), nitrogen dioxide (NO2), and water vapor (H2O). A customized vibration-resistance cavity layout incorporated with N2 purging on high-reflection mirror surfaces was implemented with a red light-emitting diode (LED) as a light source. In general, this system achieved over 40 km (up to 101.5 km) of effective light path length at 662 nm from a 0.52 m long cavity. For accurate NO3 measurement, the measured absorption spectrum of H2O was used for simultaneous concentration retrievals with the other species instead of being treated as interferences to be removed or corrected prior to NO3 detection. Synthesized N2O5 crystals under atmospheric pressure were used for performance tests of linear response and transmission efficiency. From the standard injection experiments of NO3, NO2, and H2O, high linearities were observed (R2≥0.9918). The total NO3 transmission efficiency through the system was determined to be 81.2 % (±2.9, 1σ) within the residence time of 2.59 s. The precisions (1σ) of NO3, NO2, and H2O in 1 Hz measurement from a single pixel on the charge-coupled device (CCD) were 1.41 pptv, 6.92 ppbv, and 35.0 ppmv with uncertainties of 10.8 %, 5.2 %, and ≥20.5 %, respectively, mainly from the errors in the literature absorption cross-section. The instrument was successfully deployed aboard the Korean icebreaker R/V Araon for an expedition conducted in the remote marine boundary layer in the Arctic Ocean during the summer of 2021.

Evaluation of spectral radiative properties of gases in high-pressure combustion

Radiative heat transfer affects local flame temperatures, and thus pollutant formation in high-pressure diffusion flames but the radiation properties of major gas species at pressures and temperatures relevant for combustion engines are not well known. In order to facilitate radiative transfer calculations in these types of flames, new and already published CO2 and H2O absorption spectra at high pressure and temperatures have been used to validate their modelled spectra based on the HITEMP 2010 database. Corrections for non-Lorentzian behavior of collisional-broadened lines have been evaluated, where an adjustable pseudo-Lorentzian line profile has been correlated for CO2 − N2 mixtures over a wide range of pressure, temperature and concentration. A fixed pseudo-Lorentzian line profile was found to give similar performance to previous empirical line corrections when comparing to available experimental H2O data over a relatively wide pressure and temperature range. The work has led to the release of an in-house MATLAB code, named RadISpeC freely available for download. The code efficiently produces spectra for radiation calculations for both soot and gas at high pressures and temperature.

Spectral analysis of H2O near 7180 cm–1 to accurately measure trace moisture in N2 gas: evaluation of line shape profiles using Akaike Information Criterion

The absorption spectra of H2O in N2 gas were measured at atmospheric pressure and room temperature near 7180 cm–1 in the moisture range of 9.7–148.7 nmol mol−1 in mole fraction using cavity ring-down spectroscopy. The line shape profiles used for the spectral analysis for the trace moisture measurement were evaluated based on the Akaike Information Criterion as well as the fitting residuals. The optimal line shape profile in this study was the speed-dependent asymmetric Voigt profile (SDAVP). From the comparison of the fitting results calculated using the Lorentzian profile (LP) with those calculated using the SDAVP, the relative difference in the integrated line area between the two line shape profiles was found to be systematic and constant. The measurement error due to the use of the LP could be corrected using a correction factor of 1.00479 ± 0.00077.

Impact of Residual Water Vapor on the Simultaneous Measurements of Trace CH4 and N2O in Air with Cavity Ring-Down Spectroscopy

Methane (CH4) and nitrous oxide (N2O) are among the most important atmospheric greenhouse gases. A gas sensor based on a tunable 7.6 μm continuous-wave external-cavity mode-hop-free (EC-MHF) quantum cascade laser (from 1290 to 1350 cm−1) cavity ring-down spectroscopy (CRDS) technique was developed for the simultaneous detection of CH4 and N2O in ambient air with water vapor (H2O) mostly removed via molecular sieve drying to minimize the impact of H2O on the simultaneous measurements. Still, due to the broad and strong absorption spectrum of H2O in the entire mid-infrared (mid-IR) spectral range, residual H2O in the dried ambient air due to incomplete drying and leakage, if not properly accounted for, could cause a significant influence on the measurement accuracy of the simultaneous CH4 and N2O detection. In this paper, the impact of residual H2O on the simultaneous CH4 and N2O measurements were analyzed by comparing the CH4 and N2O concentrations determined from the measured spectrum in the spectral range from 1311 to 1312.1 cm−1 via simultaneous CH4 and N2O measurements and that determined from the measured spectrum in the spectral range from 1311 to 1313 cm−1 via simultaneous CH4, N2O, and H2O measurements. The measured dependence of CH4 and N2O concentration errors on the simultaneously determined H2O concentration indicated that the residual H2O caused an under-estimation of CH4 concentration and over-estimation of N2O concentration. The H2O induced CH4 and N2O concentration errors were approximately linearly proportional to the residual H2O concentration. For the measurement of air flowing at 3 L per min, the residual H2O concentration was stabilized to approximately 14 ppmv, and the corresponding H2O induced errors were −1.3 ppbv for CH4 and 3.7 ppbv for N2O, respectively.

Influence of Y2O3/Al2O3 ratio on structure and enhanced emission properties of Ho3+-doped sol-gel high silica glasses

In this work, we have reported on enhanced emission in Ho3+-doped sol-gel high silica glasses by doped Y2O3. Effects of Y2O3/Al2O3 ratio on the structural and optical properties of Ho3+-doped glasses were investigated. According to the analysis of Si 2p3/2 XPS, 27Al NMR, FTIR, it can be concluded that the Y2O3 has greatly changed the structure of the high silica glass. The 27Al NMR spectra showed that the population of Ho3+ ions in the vicinity of Al3+ decreased with an increase in the Y2O3/Al2O3 ratio. Judd–Ofelt parameters have been evaluated from absorption spectrum of Ho3+-doped glass and predicted the high asymmetric coordination environment around Ho3+ when incorporating Y3+ into the glass network. The 2.0-μm fluorescence intensity, fluorescence lifetime and σems × τrad of Ho3+-doped glasses steadily increase with the increase in the ratio of Y2O3/Al2O3. These results suggest that Y2O3 has a good dispersion homogeneity for Ho3+ ions in high silica glass.

Two-Dimensional Temperature Measurement in a High-Temperature and High-Pressure Combustor Using Computed Tomography Tunable Diode Laser Absorption Spectroscopy (CT-TDLAS) with a Wide-Scanning Laser at 1335-1375 nm.

Tunable diode laser absorption spectroscopy (TDLAS) technology is a developing method for temperature and species concentration measurements with the features of non-contact, high precision, high sensitivity, etc. The difficulty of two-dimensional (2D) temperature measurement in actual combustors has not yet been solved because of pressure broadening of absorption spectra, optical accessibility, etc. In this study, the combination of computed tomography (CT) and TDLAS with a wide scanning laser at 1335-1375 nm has been applied to a combustor for 2D temperature measurement in high temperature of 300-2000 K and high pressure of 0.1-2.5 MPa condition. An external cavity type laser diode with wide wavelength range scanning at 1335-1375 nm was used to evaluate the broadened H2O absorption spectra due to the high-temperature and high-pressure effect. The spectroscopic database in high temperature of 300-2000 K and high pressure of 0.1-5.0 MPa condition has been revised to improve the accuracy for temperature quantitative analysis. CT reconstruction accuracy was also evaluated in different cases, which presented the consistent temperature distribution between CT reconstruction and assumed distributions. The spatial and temporal distributions of temperature in the high-temperature and high-pressure combustor were measured successfully by CT-TDLAS using the revised spectroscopic database.

A broadband Tm/Ho-doped fiber laser tunable from 1.8 to 2.09 µm for intracavity absorption spectroscopy

A broadband tunable Tm/Ho-doped fiber laser is developed for sensitive in situ measurements of intracavity absorption spectra in the spectral range of 4780–5560 cm−1. This spectral range includes an atmospheric transmission window enabling sensitive measurements of various species. The spectral bandwidth of laser emission varies from 20 to 60 cm−1 and is well suitable for multicomponent spectroscopy. The sensitivity achieved in cw operation corresponds to an effective absorption path length of Leff = 20 km, with a spectral noise of less than 1%. The spectroscopic system is applied for measurements of absorption spectra of H2O, NH3 and for simultaneous in situ detection of three isotopes of CO2 in human breath, which is important for medical diagnostics procedures.

Superconducting integrated terahertz receiver for spectral analysis of gas compounds

A new highly sensitive device for analysis of gas compounds in terahertz frequency range based on the superconducting integrated receiver is being developed. Such receiver for spectral research of Earth atmosphere from balloon-borne instrument was developed earlier in Kotel'nikov Institute of Radio Engineering and Electronics and successfully operated during several flight missions. In this work, the laboratory setup for gas spectroscopy in the range of 450-700 GHz with the noise temperature below 150 K and spectral resolution better than 0.5 MHz is presented. First results of measurements of NH3 and H2O absorption spectra are obtained.

Supercontinuum based absorption spectrometer for cycle-resolved multiparameter measurements in a rapid compression machine.

A broadband supercontinuum (SC) based absorption spectrometer capable of cycle-resolved multiparameter measurements at internal combustion (IC) engine conditions is presented. Three parameters, temperature, pressure and water mole fraction, were extracted from broadband near-infrared H2O absorption spectra, spanning the wavelength-range from 1340 to 1405.5 nm, which exhibits a large number of specific H2O transitions. The spectrometer is based on spatial domain detection and features a near-infrared line scan camera as a detector. Measurements were performed during a compression cycle of a rapid compression machine comprising a pressure and temperature range from 2.5 to 65 bar and 300 to 900 K, respectively. With the new spectrometer, we are for the first time, based on the authors' knowledge, able to perform measurements based on SC radiation over a complete compression and expansion stroke at measurement rates up to 50 kHz. A detailed overview is provided about the best match algorithm between theory and experiments, including parameters from two different spectral databases, namely the Barber-Tennyson database (BT2) and HITRAN2012. The results indicate that spectral broadening effects are not properly described by theory, especially at pressure levels exceeding 20 bar, which culminates in a clear underestimation of the derived pressure data by SC absorption spectroscopy. Nevertheless, temperature can be determined accurately by performing a three-parameter fit based on water mole fraction, temperature, and pressure. In contrast, making use of pressure transducer data as look-up values and varying only temperature and H2O mole fraction to find the best match leads to a clear overestimation of temperature at elevated pressures.

New features of an FT spectrometer using LED sources

The efficiency of LED emitters in high resolution Fourier spectroscopy with a small multipass cell has been shown. Such aspects of Fourier spectroscopy as intensity of the light sources, their stability, and spectral range were considered. Using a 2.5W LED emitter as a light source for the spectrometer with a 60-cm multipass cell during a 24-h measurement time and by optimizing a number of passes in the cell, we have achieved a signal-to-noise ratio of 1×105 which corresponds to a minimal detectable absorption coefficient of 6×10−9cm−1. This made it possible to determine the parameters of water vapor lines with the intensity of 2×10−28cm/molecule. The absorption spectra of H2O and CO2 isotopologues in the range of 10,000 to 23,000cm−1 were recorded using high sensitivity Fourier spectrometer.

2D Temperature Detection Characteristics of Engine Exhaust Gases Using CT Tunable Diode Laser Absorption Spectroscopy

Two dimensional (2D) temperature and concentration distribution is related to the combustion structure, the combustor efficiency in engines, burners, gas turbines and so on. Recently, tunable diode laser absorption spectroscopy (TDLAS) as a multi-species measurement technique with high sensitivity and high response has been developed and applied to industrial process monitoring and control technologies in combustion environments. With these engineering developments, transient phenomena such as start-ups and load changes in engines have been gradually elucidated in various conditions. This paper discusses a study of the fast response 2D temperature distribution measurement method based on the combination of TDLAS and Computed Tomographic (CT) reconstruction using absorption spectra of water vapor at 1388nm. The computed tomography tunable diode laser absorption spectroscopy (CTTDLAS) method was appliedtoengine exhausts for 2D temperature distribution measurements. The measured 2D temperature showed better characteristics compared with the temperature measured by a thermocouple. Theoretical H2O absorption spectra in the 1388 nm near-infrared region calculated by the revised HITRAN database were used for temperature measurement. For accurate measurement of temperature in combustion gases, the spectroscopic databases were modified using experimentally measured spectral parameters that are not found in the databases. Accuracy of temperature measurement using TDLAS have also been discussed to demonstrate its applicability to various types of combustor.

Structural and Optical Properties of Ho<sup>3+</sup> Doped ZnO-Bi<sub>2</sub>O<sub>3</sub>-B<sub>2</sub>O<sub>3</sub> Glasses

Ho3+ doped zinc bismuth borate glasses of the composition 10ZnO : 30Bi2O3 : (60-x)B2O3 : xHo2O3 (where x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 mol%) were fabricated by conventional melt quenching technique. In order to understand the role of Ho2O3 in these glasses, the density, molar volume and optical spectra were investigated. The molar volume decreases with an increase in Ho2O3 content, which is attributed to the structure becomes more compacted. The absorption spectra of Ho3+ doped in zinc bismuth borate glass correspond to several bands, which are assigned from the ground state, 5I8 to 5G5 (420 nm), 5G6 + 5F1 (451 nm), 5F2 + 5F4 (538 nm), 5F5 (643 nm) and 5I5 (1152 nm). Moreover, the optical basicities were also theoretically determined.

Calibration-free sensor for pressure and H2O concentration in headspace of sterile vial using tunable diode laser absorption spectroscopy

Tunable diode laser absorption measurements of pressure and H2O concentration in the headspace of vials using a distributed-feedback (DFB) diode laser near 1.4 μm are reported. A H2O line located near 7161.41 cm(-1) is selected based on its strong absorption strength and isolation from interference of neighboring transitions. Direct absorption spectra of H2O are obtained for the measurement path as well as the reference path by scanning the laser wavelength. The pressure and H2O vapor concentration in the headspace of a vial are inferred from a differential absorption signal, which is the difference between the measured and the referenced absorbance spectra. This sensor is calibration-free and no purge gas is needed. The demonstrated capability would enable measurements of pressure and H2O concentration in the headspace of vials within 2.21% and 2.86%, respectively. A precision of 1.02 Torr and 390 ppm is found for the pressure and H2O concentration, respectively. A set of measurements for commercial freeze-dried products are also performed to illustrate the usefulness of this sensor.

A Study of the Physical and Optical Properties of Ho<sup>3+</sup> in Soda-Lime-Silicate Glass Systems

Soda-lime-silicate glasses in the compositions of (65-x)SiO2-25Na2O-10CaO-xHo2O3 (where x = 0.0, 0.50, 1.00, 1.50, 2.00 and 2.50 mol % ) were prepared by melt-quenching technique and characterized. The results show that, the absorption spectra of Ho3+ doped in soda-lime-silicate glass correspond with several bands, which are assigned from the ground state, 5I8 to 3H6 (360 nm), 5G4 (380 nm), 5G5 (417 nm), 5G6 (453 nm), 5F3 (479 nm), 5F4 (538 nm), 5F5 (639 nm), and 5I5 (880 nm). The refractive index and density of glasses were increase with increasing of Ho2O3 concentration. The color of glass samples is light amber with doped Ho2O3 in glass matrix.

Infrared molar absorption coefficient of H2O stretching modes in SiO2

Infrared absorption of the H2O stretching modes around 3400cm−1 is commonly used to detect the presence of H2O inside SiO2. Obtaining the exact concentration of water remains difficult since the molar absorption coefficient (ε) is not known. In this work ε is determined for H2O absorbed in sub-atmospheric chemical vapor deposited SiO2 and compared to liquid water. By integration over the whole absorption band width, ε is found to be 7.64±1.08×104M−1cm−2. When considering peak absorption at the absorption band maximum only, the value is ε=139.5±11.8M−1cm−1 which is significantly lower than the literature value of liquid water for which ε=231.66±0.05M−1cm−1. This difference is attributed to the absence of hydrogen bridges between H2O molecules, evidenced by the featureless absorption spectrum of H2O inside SiO2.

Fiber-coupled 2.7 µm laser absorption sensor for CO2 in harsh combustion environments

A tunable diode laser absorption sensor near 2.7 µm, based on 1f-normalized wavelength-modulation spectroscopy with second-harmonic detection (WMS-2f), was developed to measure CO2 concentration in harsh combustion flows. Wavelength selection at 3733.48 cm−1 exploited the overlap of two CO2 transitions in the ν1 + ν3 vibrational band at 3733.468 cm−1 and 3733.498 cm−1. Primary factors influencing wavelength selection were isolation and strength of the CO2 absorption lines relative to infrared water absorption at elevated pressures and temperatures. The HITEMP 2010 database was used to model the combined CO2 and H2O absorption spectra, and key line-strength and line-broadening spectroscopic parameters were verified by high-temperature static cell measurements. To validate the accuracy and precision of the WMS-based sensor, measurements of CO2 concentration were carried out in non-reactive shock-tube experiments (P ∼ 3–12 atm, T ∼ 1000–2600 K). The laser was then free-space fiber-coupled with a zirconium fluoride single-mode fiber for remote light delivery to harsh combustion environments, and demonstrated on an ethylene/air pulse detonation combustor at pressures up to 10 atm and temperatures up to 2500 K. To our knowledge, this work represents the first time-resolved in-stream measurements of CO2 concentration in a detonation-based engine.

A new analysis of the ν2 fundamental band of H2O+*

This paper reports that the absorption spectra of H2O+ have been measured by tunable mid-infrared diode laserspectroscopy in the spectral range of 1100–1380 cm-1. The H2O+ ions are generated in an AC glow discharge of the gaseous mixtures of H2O/He and detected with the velocity modulation technique. Forty new lines are assigned to theν2 fundamental band of H2O+(X̄2B1). The observed lines together with other data published previously are fitted to the standard effective Hamiltonian of an asymmetric top, yielding a set of improved rotational constants, spin-rotation constants and their quartic and sextic centrifugal distortion constants for the ν2=1 vibrational state of H2O+.