Evaluation of the effect of the 2011 Tsunami on coastal forests by means of multiple isotopic analyses of tree-rings

The March 2011 Mega-Tsunami in eastern Japan damaged at different degrees the black pine (Pinus thunbergii) forests along the coast. In order to evaluate the recovery of black pine four years later, tree-ring samples from 9 trees for the period 2002–2014 were analyzed for ring growth and stable isotopes (δ¹³C, δ¹⁵N and δ¹⁸O). The results showed that annual tree-ring width decreased approximately 70?% from the year 2011 to 2014 compared to the period previous to the tsunami (2002–2010). The multiple isotopic analyses showed that the reduction in growth was caused by soil salinity that prompted stomatal closure and an abrupt increase of tree-ring δ¹³C. Sea water deposition in the soil did not affect tree-ring δ¹⁸O values. Two years after the tsunami, decreasing tree-ring δ¹³C values caused by apparently photosynthetic recovery did not translate into radial tree-growth, indicating a possible shift in carbon allocation to foliage and mainly roots as a defense mechanism to sodium toxicity. The dual δ¹³C-δ¹⁸O model explains neither the limited growth nor the subsequent recovery in δ¹³C. Similarly tree-ring δ¹⁵N indicated that there was no difference in nitrogen availability before and after the tsunami, suggesting that nutrients were not a limitation but rather soil salinity.     

In situ measurement of CO2 and water vapour isotopic compositions at a forest site using mid-infrared laser absorption spectroscopy

We conducted continuous, high time-resolution measurements of CO₂ and water vapour isotopologues (¹⁶O¹²C¹⁶O, ¹⁶O¹³C¹⁶O and ¹⁸O¹²C¹⁶O for CO₂, and H₂¹⁸O for water vapour) in a red pine forest at the foot of Mt. Fuji for 9 days from the end of July 2010 using in situ absorption laser spectroscopy. The δ¹⁸O values in water vapour were estimated using the δ²H–δ¹⁸O relationship. At a scale of several days, the temporal variations in δ¹⁸O-CO₂ and δ¹⁸O-H₂O are similar. The orders of the daily Keeling plots are almost identical. A possible reason for the similar behaviour of δ¹⁸O-CO₂ and δ¹⁸O-H₂O is considered to be that the air masses with different water vapour isotopic ratios moved into the forest, and changed the atmosphere of the forest. A significant correlation was observed between δ¹⁸O-CO₂ and δ¹³C-CO₂ values at nighttime (r²≈0.9) due to mixing between soil (and/or leaf) respiration and tropospheric CO₂. The ratios of the discrimination coefficients (Δ_a/Δ) for oxygen (Δ_a) and carbon (Δ) isotopes during photosynthesis were estimated in the range of 0.7–1.2 from the daytime correlations between δ¹⁸O-CO₂ and δ¹³C-CO₂ values.     

Seasonal variation of oxygen-18 in precipitation and surface water of the Poyang Lake Basin,China

Based on the monthly δ¹⁸O value measured over a hydrology period in precipitation, runoff of five tributaries and the main lake of the Poyang Lake Basin, combined with hydrological and meteorological data, the characteristics of δ¹⁸O in precipitation (δ¹⁸O_PPT) and runoff (δ¹⁸O_SUR) are discussed. The δ¹⁸O_PPT and δ¹⁸O_SUR values range from?2.75 to?14.12 ‰ (annual mean value=?7.13 ‰ ) and from?2.30 to?8.56 ‰, respectively. The seasonal variation of δ¹⁸O_PPT is controlled by the air mass circulation in this region, which is dominated by the Asian summer monsoon and the Siberian High during winter. The correlation between the wet seasonal averages of δ¹⁸O_SUR in runoff of the rivers and δ¹⁸O_PPT of precipitation at the corresponding stations shows that in the Poyang Lake catchment area the river water consists of 23% direct runoff (precipitation) and 77% base flow (shallow groundwater). This high proportion of groundwater in the river runoff points to the prevalence of wetland conditions in the Poyang Lake catchment during rainy season. Considering the oxygen isotopic composition of the main body of Poyang Lake, no isotopic enrichment relative to river inflow was found during the rainy season with maximum expansion of the lake. Thus, evaporation causing isotopic enrichment is a minor component of the lake water balance in the rainy period. During dry season, a slight isotopic enrichment has been observed, which suggests a certain evaporative loss of lake water in that period.     

δ2H and δ18O of human body water: a GIS model to distinguish residents from non-residents in the contiguous USA

An understanding of the factors influencing the isotopic composition of body water is important to determine the isotopic composition of tissues that are used to reconstruct movement patterns of humans. The δ²H and δ¹⁸O values of body water (δ²H_bw and δ¹⁸O_bw) are related to the δ²H and δ¹⁸O values of drinking water (δ²H_dw and δ¹⁸O_dw), but clearly distinct because of other factors including the composition of food. Here, we develop a mechanistic geographical information system (GIS) model to produce spatial projections of δ²H_bw and δ¹⁸O_bw values for the USA. We investigate the influence of gender, food, and drinking water on the predicted values by comparing them with the published values. The strongest influence on the predicted values was related to the source of δ²H_dw and δ¹⁸O_dw values. We combine the model with equations that describe the rate of turnover to produce estimates for the time required for a non-resident to reach an isotopic equilibrium with a resident population.     

Oxides of long carbon chains: Results obtained on IR and UV-vis absorptions

The IR and UV-vis absorptions of oxides of long carbon chains trapped in cryogenic matrices were investigated experimentally and theoretically. Some of the IR-lines were assigned to the oxides of certain carbon chains using the method of isotopic substitution of matrix material (¹⁶O₂/¹⁸O₂, ¹²CO/¹³CO) and the technique of selective UV-vis photo-bleaching. Our data, along with quantum chemical calculations suggest that the wavelength positions of the major UV-vis and IR absorptions of the oxides C_nO, OC_nO, and of the parent carbon chains C_n are located in close vicinity.     

Influence of air pollution and site conditions on trends of carbon and oxygen isotope ratios in tree ring cellulose

Oxygen and carbon isotopic compositions of tree ring cellulose (delta13Ccell and delta18Ocell) were measured for pines growing at four sites in east Germany. Three sites differed markedly in soil water availability within a short distance and the fourth site served as a reference. The choice of the sites was guided by the desire to detect effects of air pollution on the long-term trend of isotopic compositions and to examine the influence of soil water availability on the relationship between the carbon and oxygen isotope ratios. Locations in east Germany are particularly well suited for the study of pollution effects because there was a steady increase in environmental contamination until the German Reunification in 1990, followed by a sharp decline due to the implementation of stricter environmental standards. The long-term trend of delta13Ccell showed an extraordinary increase in the period 1945-1990 and a rapid decrease after 1990, whereas delta18Ocell remained nearly constant. The increase of delta13Ccell is explained by secondary fractionation caused by phytotoxicity of SO2. Two effects are mainly responsible for the secondary fractionation under SO2 exposure: increase of dark respiration, and changes in photosynthate allocation and partitioning. Both effects do not influence delta18Ocell. Furthermore, a significant positive correlation between the year-to-year variations of carbon and oxygen isotope ratios (delta13Cresid and delta18Oresid) has been found for all sites. The slopes of the relationship between delta13Cresid and delta18Oresid differ insignificantly. It is concluded that this relationship is not influenced by soil water availability but by climatic variables.     

Soil matrix tracer contamination and canopy recycling did not impair 13CO2 plant–soil pulse labelling experiments

When conducting ¹³CO₂ plant–soil pulse labelling experiments, tracer material might cause unwanted side effects which potentially affect δ¹³C measurements of soil respiration (δ¹³C_SR) and the subsequent data interpretation. First, when the soil matrix is not isolated from the atmosphere, contamination of the soil matrix with tracer material occurs leading to a physical back-diffusion from soil pores. Second, when using canopy chambers continuously, ¹³CO₂ is permanently re-introduced into the atmosphere due to leaf respiration which then aids re-assimilation of tracer material by the canopy. Accordingly, two climate chamber experiments on European beech saplings (Fagus sylvatica L.) were conducted to evaluate the influence of soil matrix ¹³CO₂ contamination and canopy recycling on soil ¹³CO₂ efflux during ¹³CO₂ plant–soil pulse labelling experiments. For this purpose, a combined soil/canopy chamber system was developed which separates soil and canopy compartments in order to (a) prevent diffusion of ¹³C tracer into the soil chamber during a ¹³CO₂ canopy pulse labelling and (b) study stable isotope processes in soil and canopy individually and independently. In combination with laser spectrometry measuring CO₂ isotopologue mixing ratios at a rate of 1 Hz, we were able to measure δ¹³C in canopy and soil at very high temporal resolution. For the soil matrix contamination experiment, ¹³CO₂ was applied to bare soil, canopy only or, simultaneously, to soil and canopy of the beech trees. The obtained δ¹³C_SR fluxes from the different treatments were then compared with respect to label re-appearance, first peak time and magnitude. By determining the δ¹³C_SR decay of physical ¹³CO₂ back-diffusion from bare soils (contamination), it was possible to separate biological and physical components in δ¹³C_SR of a combined flux of both. A second pulse labelling experiment, with chambers permanently enclosing the canopy, revealed that ¹³CO₂ recycling at canopy level had no effect on δ¹³C_SR dynamics.     

Stable carbon isotopes in dissolved inorganic carbon: extraction and implications for quantifying the contributions from silicate and carbonate weathering in the Krishna River system during peak discharge

We present a comparative study of two offline methods, a newly developed method and an existing one, for the measurement of the stable carbon isotopic composition (δ¹³C) of dissolved inorganic carbon (DIC; δ¹³C_DIC) in natural waters. The measured δ¹³C_DIC values of different water samples, prepared from laboratory Na₂CO₃, ground and oceanic waters, and a laboratory carbonate isotope standard, are found to be accurate and reproducible to within 0.5 ‰\ (1σ). The extraction of CO₂ from water samples by these methods does not require pre-treatment or sample poisoning and can be applied to a variety of natural waters to address carbon cycling in the hydrosphere. In addition, we present a simple method (based on a two-end-member mixing model) to estimate the silicate-weathering contribution to DIC in a river system by using the concentration of DIC and its δ¹³C. This approach is tested with data from the Krishna River system as a case study, thereby quantifying the contribution of silicate and carbonate weathering to DIC, particularly during peak discharge.     

Isotopic fractionation between gaseous and condensed carbon dioxide

The isotopic fractionation in the equilibrium liquid-vapour system of carbon dioxide has been measured for both the carbon and oxygen isotopic species in the temperature range 220–303 °K (Fig. 1). The¹²C¹⁶O¹⁸O isotopic species is somewhat less, and¹³C¹⁶O₂ slightly more volatile than¹²C¹⁶O₂, while the fractionation in both cases approaches zero at the critical temperature. The theoretical expression derived for isotopic fractionation in two phase equilibria qualitatively accounts for the observed direction of the enrichment but fails to explain its disappearance at the critical point. A temperature dependence of the binding energy and intermolecular vibration frequency is proposed to bring the theory into accordance with observation. The magnitude of the unknown term in the fractionation caused by internal effects (including hindered rotation) is obtained by subtraction. It is of the same order of magnitude as the other terms.     

Spatial and seasonal variations in the stable C isotope composition of dissolved inorganic carbon and in physico-chemical water parameters in the Plitvice Lakes system

Plitvice Lakes waters were collected at 14 sampling points, including springs, tributaries and lakes, for the period 2002–2007. The results of the physical and chemical conditions of calcite precipitation as well as the δ¹³C values of dissolved inorganic carbon (DIC) were used to study the processes influencing calcite precipitation. Significant differences between spring, lake and stream waters as well as changes in the downstream direction were observed. The correlation between δ¹³C_DIC values and physico-chemical conditions for calcite precipitation showed that calcite precipitates in lake waters which are oversaturated with respect to CaCO₃ (I _sat values 4–10) and with δ¹³C_DIC values between?11.5 and?8.5 ‰. In spring waters, the δ¹³C_DIC values were more negative, from?14 to?12 ‰, and I _sat values of 1–2 indicated that equilibrium conditions for calcite precipitation were not attained. The downstream increase in δ¹³C_DIC correlated with the increase in the δ¹³C values of calcite in the lake sediments, suggesting that the freshwater calcite was mainly of autochthonous origin and precipitated within the water column in isotopic equilibrium with DIC.     

Field-based cavity ring-down spectrometry of δ13C in soil-respired CO2

Measurement of soil-respired CO₂ at high temporal resolution and sample density is necessary to accurately identify sources and quantify effluxes of soil-respired CO₂. A portable sampling device for the analysis of δ¹³C values in the field is described herein.

CO₂ accumulated in a soil chamber was batch sampled sequentially in four gas bags and analysed by Wavelength-Scanned Cavity Ring-down Spectrometry (WS-CRDS). A Keeling plot (1/[CO₂] versus δ¹³C) was used to derive δ¹³C values of soil-respired CO₂. Calibration to the δ¹³C Vienna Peedee Belemnite scale was by analysis of cylinder CO₂ and CO₂ derived from dissolved carbonate standards. The performance of gas-bag analysis was compared to continuous analysis where the WS-CRDS analyser was connected directly to the soil chamber.

Although there are inherent difficulties in obtaining absolute accuracy data for δ¹³C values in soil-respired CO₂, the similarity of δ¹³C values obtained for the same test soil with different analytical configurations indicated that an acceptable accuracy of the δ¹³C data were obtained by the WS-CRDS techniques presented here. Field testing of a variety of tropical soil/vegetation types, using the batch sampling technique yielded δ¹³C values for soil-respired CO₂ related to the dominance of either C₃ (tree, δ¹³C=?27.8 to?31.9 ‰) or C₄ (tropical grass, δ¹³C=?9.8 to?13.6 ‰) photosynthetic pathways in vegetation at the sampling sites. Standard errors of the Keeling plot intercept δ¹³C values of soil-respired CO₂ were typically<0.4 ‰ for analysis of soils with high CO₂ efflux (>7–9 μmol m^?2 s^?1).     

Isotopic Assessment of Sources and Processes Affecting Sulfate and Nitrate in Surface Water and Groundwater of Luxembourg

Abstract

Surface water and deep and shallow groundwater samples were taken from selected parts of the Grand-Duchy of Luxembourg to determine the isotopic composition of nitrate and sulfate, in order to identify sources and/or processes affecting these solutes. Deep groundwater had sulfate concentrations between 20 and 40mg/L, δ³⁴S_sulfate values between ?3.0 and ?20.0‰, and δ¹⁸O_sulfate values between +1.5 and +5.0‰ nitrate was characterized by concentrations varying between <0.5 and 10mg/L, δ¹⁵N_nitrate values of ～?0.5‰, and δ¹⁸O_nitrate values ～+3.0‰. In the shallow groundwater, sulfate concentrations ranged from 25 to 30mg/L, δ³⁴S_sulfate values from ?20.0 to +4.5‰, and δ¹⁸O_sulfate values from ～+0.5 to +4.5‰ nitrate concentrations varied between ～10 and 75mg/L, δ¹⁵N_nitrate values between +2.5 and +10.0‰, and δ¹⁸O_nitrate values between +1.0 and +3.0‰. In surface water, sulfate concentrations ranged from 10 to 210mg/L, δ³⁴S_sulfate values varied between ?9.3 and +10.9‰, and δ¹⁸O_sulfate values between +3.0 and +10.7‰ were observed. Nitrate concentrations ranged from 10 to 40mg/L, δ¹⁵N_nitrate values from +6.5 to +12.0‰, and δ¹⁸O_nitrate values from ?0.4 to +4.0‰. Based on these data, three sulfate sources were identified controlling the riverine sulfate load. These are soil sulfate, dissolution of evaporites, and oxidation of reduced S minerals in the bedrock. Both groundwater types were predominantly influenced by sulfate from the two latter lithogenic S sources. The deep groundwater and a couple shallow groundwater samples had nitrate derived mainly from soil nitrification. All other sampling sites were influenced by nitrate originating from sewage and/or manure. A decrease in nitrate concentration observed along one of the rivers was attributed to denitrification. It appears that sulfate within Luxembourg's aquatic ecosystem is mainly of lithogenic origin, whereas nitrate is often derived from anthropogenic activities.     

Reliability of stable carbon and oxygen isotope compositions of pedogenic needle fibre calcite as environmental indicators: examples from Western Europe

Stable carbon and oxygen isotope analyses were conducted on pedogenic needle fibre calcite (NFC) from seven sites in areas with roughly similar temperate climates in Western Europe, including the Swiss Jura Mountains, eastern and southern France, northern Wales, and north-eastern Spain. The δ¹³C values (?12.5 to?6.8 ‰ Vienna Pee Dee Belemnite (VPDB)) record the predominant C₃ vegetation cover at the sites. A good correlation was found between mean monthly climatic parameters (air temperature, number of frost days, humidity, and precipitation) and δ¹⁸O values (?7.8 to?3.4‰ VPDB) of all the NFC. Similar seasonal variations of δ¹⁸O values for monthly NFC samples from the Swiss sites and those of mean monthly δ¹⁸O values of local precipitation and meteorological data point out precipitation and preferential growth/or recrystallisation of the pedogenic needle calcite during dry seasons. These covariations indicate the potential of stable isotope compositions of preserved NFC in fossil soil horizons as a promising tool for palaeoenvironmental reconstructions.     

Continuous measurements of stable isotopes of carbon dioxide and water vapour in an urban atmosphere: isotopic variations associated with meteorological conditions

Isotope ratios of carbon dioxide and water vapour in the near-surface air were continuously measured for one month in an urban area of the city of Nagoya in central Japan in September 2010 using laser spectroscopic techniques. During the passages of a typhoon and a stationary front in the observation period, remarkable changes in the isotope ratios of CO₂ and water vapour were observed. The isotope ratios of both CO₂ and water vapour decreased during the typhoon passage. The decreases can be attributed to the air coming from an industrial area and the rainout effects of the typhoon, respectively. During the passage of the stationary front, δ¹³C–CO₂ and δ¹⁸O–CO₂ increased, while δ²H–H₂Ov and δ¹⁸O–H₂Ov decreased. These changes can be attributed to the air coming from rural areas and the air surrounding the observational site changing from a subtropical air mass to a subpolar air mass during the passage of the stationary front. A clear relationship was observed between the isotopic CO₂ and water vapour and the meteorological phenomena. Therefore, isotopic information of CO₂ and H₂Ov could be used as a tracer of meteorological information.     

A (nearly) complete experimental linelist for CO2, OCO, OCO, CO2 and OCO by high-sensitivity CW-CRDS spectroscopy between 5851 and 7045 cm

An experimental database for the ¹³C¹⁶O₂, ¹⁶O¹³C¹⁸O, ¹⁶O¹³C¹⁷O, ¹³C¹⁸O₂ and ¹⁷O¹³C¹⁸O isotopologues of carbon dioxide has been constructed on the basis of the high-sensitivity absorption spectrum of carbon dioxide with 99% enrichment in ¹³C recorded by CW-cavity ring down spectroscopy (CW-CRDS) between 5851 and 7045 cm⁻¹. As a result of the achieved sensitivity (typical noise equivalent absorption α_min∼2-5×10⁻¹⁰ cm⁻¹) combined with the high linearity and dynamics (more than four decades) of the CW-CRDS technique, the amount of spectroscopic information contained in these spectra was considerable. A total of 8639 transitions of the ¹³C¹⁶O₂, ¹⁶O¹³C¹⁸O, ¹⁶O¹³C¹⁷O, ¹³C¹⁸O₂ and ¹⁷O¹³C¹⁸O isotopologues with line strength as low as 5×10⁻²⁹ cm/molecule were assigned. They belong to a total of 150 bands, while less than 20 bands were previously reported by Fourier transform spectroscopy. The excellent agreement between the predictions of the effective operators model and the observations has allowed using an automatic search program to assign the weaker lines observed in the congested spectrum. The spectroscopic parameters of the vibrational upper levels were obtained from a fit of the measured line positions. A number of resonance interactions were observed; in particular, several occurrences of interpolyad anharmonic couplings not included in the polyad model of effective Hamiltonian, were found to affect a few bands of the ¹⁶O¹³C¹⁸O and ¹⁶O¹³C¹⁷O isotopologues. In the list of 8639 transitions, which are provided as Supplementary material, line positions are experimental values (typical uncertainty in the order of 1×10⁻³ cm⁻¹), while line strengths were calculated at 296 K by using the effective operators approach (typical uncertainty in the order of 5%). In the case of the ¹³C¹⁶O₂ isotopologue, the reported transitions represent 99.65% of the total absorbance in the region considered.     

High sensitivity CW-Cavity Ring Down Spectroscopy of five CO2 isotopologues of carbon dioxide in the 1.26-1.44 μm region (I): Line positions

The absorption spectrum of highly enriched ¹³C carbon dioxide has been investigated by CW-Cavity Ring Down Spectroscopy with a setup based on fibered distributed feedback (DFB) laser diodes. By using a series of 30 DFB lasers, the CO₂ spectrum was recorded in the 7029-7917 cm⁻¹ region with a typical sensitivity of 3×10⁻¹⁰ cm⁻¹. The uncertainty on the determined line positions is on the order of 8×10⁻⁴ cm⁻¹. More than 3800 transitions with intensities as low as 1×10⁻²⁹ cm/molecule were detected and assigned to the ¹³C¹⁶O₂, ¹⁶O¹³C¹⁷O, ¹⁶O¹³C¹⁸O, ¹⁷O¹³C¹⁸O and ¹³C¹⁸O₂ isotopologues. For comparison, only 104 line positions of ¹³C¹⁶O₂ were previously reported in the literature in the considered region. The band-by-band analysis has led to the determination of the rovibrational parameters of a total of 83 bands including 56 bands of the ¹³C¹⁶O₂ species. The measured line positions of ¹³C¹⁶O₂ and ¹⁶O¹³C¹⁸O were found in good agreement with the predictions of the respective effective Hamiltonian (EH) models but the agreement degrades for the minor isotopologues. Several cases of resonance interactions were found and discussed. In the 20033-10002 band of ¹³C¹⁶O₂, an anharmonic resonance interaction leads to deviations on the order of 0.05 cm⁻¹ compared to the EH predictions. The existence of interpolyad interactions affecting the non-symmetric isotopologues of carbon dioxide is confirmed by the observation of two occurrences in ¹⁶O¹³C¹⁷O and ¹⁶O¹³C¹⁸O. The obtained results improve significantly the knowledge of the spectroscopy of the ¹³C isotopologues of carbon dioxide. They will be valuable to refine the sets of effective Hamiltonian parameters used to generate the CDSD database.     

Isotopic fractionation between gaseous and dissolved carbon dioxide

The isotopic fractionation between gaseous carbon dioxide and an equilibrated aqueous solution of the gas has been measured at temperatures between 0° and 60 °C for the carbon isotopes and close to 0 °C for the oxygen isotopes. ¹³C¹⁶O₂ is slightly less, and¹²C¹⁶O¹⁸O slightly more soluble than¹²C¹⁶O₂, the actual values for the fractionation,?, being ?(1.18?0.0041 ·t)‰ (temperature,t, in °C) for the carbon isotopes and about 0.8‰ at 0°C for the oxygen isotopes. A theoretical expression is derived for the vapour-solute equilibrium system by treating it in a similar manner as the pure vapour-liquid system. The calculated isotopic fractionation for carbon dioxide, using data on the pure vapour-liquid system, is in satisfactory agreement with the experimental results.     

Characterisation of spatial variability and patterns in tree and soil δ13C at forested sites in eastern Canada

Wholistic isotopic studies provide a necessary foundation on which to build conceptual understanding of ecosystem development processes and provide the basis for further isotopic studies at a site or within an ecophysiological region. This study seeks to broadly characterise δ¹³C spatial variability and spatial patterns within soils and canopy tissues at five forest research sites in eastern Canada. We observe consistent and predictable patterns of leaf δ¹³C variation within trees and a consistent offset between woody and leafy tree tissues. Patterns are similar for both hardwoods and softwoods, but overall hardwoods had canopies that were more depleted in ¹³C. Soil carbon δ¹³C enrichment occurred with depth and appeared to vary according to site soil texture. Upper soil δ¹³C was intermediate between leaves and woody tissues, whereas deeper soil values suggested important contributions from more enriched tree tissues, such as persistent woody debris and possibly roots. The relationship between aboveground and belowground signatures suggests functional or developmental differences between study sites.     

Spectral measurements of high-temperature isotopic carbon dioxide in the 4.5- and 2.8-μm regions

High-resolution measurements have been made using the AFGL 2-m path difference Fourier transform spectrometer on isotopically enriched samples of carbon dioxide. Two regions were investigated: 2140–2320 and 3470–3770 cm⁻¹. The samples were observed in absorption at temperatures up to 800 K. Observed line positions to high rotational levels were obtained for 15 parallel bands with Δv₃ = 1 for the isotopic variants ¹³C¹⁶O₂, ¹³C¹⁶O¹⁸O, and ¹³C¹⁶O¹⁷O in the 4.5-μm region and for 23 bands of the type Δv₁ = 1, Δv₃ = 1 for the species ¹²C¹⁶O₂, ¹²C¹⁶O¹⁸O, and ¹²C¹⁸O₂ in the 2.8-μm region.     

Highly sensitive absorption spectroscopy of carbon dioxide by ICLAS-VeCSEL between 8800 and 9530 cm

The absorption spectrum of carbon dioxide has been studied between 8800 and 9530 cm⁻¹ by intracavity laser absorption spectroscopy based on a vertical external cavity surface emitting lasers (VeCSEL). Previous laboratory spectra at high resolution were nearly absent in the considered spectral region. Experiments were carried with natural carbon dioxide and with ¹³C enriched carbon dioxide leading to the determination of the rovibrational parameters of a total of 15 very weak vibrational transitions, including two bands of the ¹⁶O¹³C¹⁸O isotopologue. The observed transitions are assigned to components of the 2ν₁ + 3ν₃ triad and of the much weaker 5ν₁ + ν₃ hexad. Our measured line positions are found in excellent agreement with the predictions of the effective Hamiltonians developed for ¹²C¹⁶O₂ and ¹³C¹⁶O₂ but significant deviations were evidenced for the ¹⁶O¹³C¹⁸O minor isotopologue. The relative band intensities within each polyad are also discussed on the basis of the effective Hamiltonian model.