Hot Band Lines Research Articles

First high resolution infrared spectra of 1-13C-Propane analyses of the ν26 (B2) C-Type, ν8 (A1) and ν9 (A1) B-Type bands

This paper presents the first high resolution (Δν = 0.00096 cm−1) IR investigation of 1-13C - propane. Spectra of the ν9 (A1) CCC skeletal bending mode near 366.40365 cm−1 (B-type band) and the ν26 (B2) methylene (CH2) rocking mode near 748.470 cm−1 (C-type band) were recorded at the Canadian Light Source (CLS) synchrotron. The spectra were assigned both traditionally and with the aid of the PGOPHER program [1]. As only limited MW data are available for this molecule, we had to use the present data to determine a new set of ground state constants that included centrifugal distortion terms. Upper state constants for both bands have been determined that provide a good simulation of the spectra. The analysis also included the strong a-Type Coriolis resonance between the ν26 and 2ν9 states that causes strong perturbation allowed transitions to appear in the spectrum. Hot band lines of the 2ν9-ν9 band were also assigned and included in our analysis of the bending region. In addition, the v8 (A1) CC stretching band at 862.076 cm−1 (B-type band) which somewhat overlapped v26 was included in the analysis as well. The hope is that this data and the derived molecular constants will be useful in identifying isotopic propane lines in Titan and other astrophysical objects.

Accurate quantum dynamics simulation of the photodetachment spectrum of the nitrate anion (NO3 -) based on an artificial neural network diabatic potential model.

The photodetachment spectrum of the nitrate anion (NO3 -) is simulated from first principles using wavepacket quantum dynamics propagation and a newly developed accurate full-dimensional fully coupled five state diabatic potential model. This model utilizes the recently proposed complete nuclear permutation inversion invariant artificial neural network diabatization technique [D. M. G. Williams and W. Eisfeld, J. Phys. Chem. A 124, 7608 (2020)]. The quantum dynamics simulations are designed such that temperature effects and the impact of near threshold detachment are taken into account. Thus, the two available experiments at high temperature and at cryogenic temperature using the slow electron velocity-map imaging technique can be reproduced in very good agreement. These results clearly show the relevance of hot bands and vibronic coupling between the X̃ 2A2 ' ground state and the B̃ 2E' excited state of the neutral radical. This together with the recent experiment at low temperature gives further support for the proper assignment of the ν3 fundamental, which has been debated for many years. An assignment of a not yet discussed hot band line is also proposed.

Pure rotation spectrum of CF4 in the v3 = 1 state using THz synchrotron radiation

Spherical-top tetrahedral species like CH4, SiH4, CF4, …possess no permanent dipole moment. Therefore, probing their pure rotation spectrum is very challenging since only a very weak dipole moment can be induced by centrifugal distortion and/or rovibrational interaction. If some Q branch lines have been recorded thanks to microwave techniques, R branch lines in the THz region have been poorly explored until recently. In previous studies, we have reported the pure rotation THz spectrum of cold and hot band lines of methane recorded at the SOLEIL Synchrotron facility. Here, we present the first recorded THz spectrum of the R branch of CF4, a powerful greenhouse gas, in its v3=1 state. This Fourier transform spectrum covers the R(20) to R(37) line clusters, in the 20–37cm−1 spectral range. It was recorded thanks to a 150m multiple path cell at room temperature. We could estimate the vibration-induced dipole moment value and also include the recorded line positions in a global fit of many CF4 transitions.

Application of the Hartmann–Tran profile to precise experimental data sets of 12C2H2

Self- and nitrogen-broadened line shape data for the Pe(11) line of the ν1+ν3 band of acetylene, recorded using a frequency comb-stabilized laser spectrometer, have been analyzed using the Hartmann–Tran profile (HTP) line shape model in a multispectrum fitting. In total, the data included measurements recorded at temperatures between 125K and 296K and at pressures between 4 and 760Torr. New, sub-Doppler, frequency comb-referenced measurements of the positions of multiple underlying hot band lines have also been made. These underlying lines significantly affect the Pe(11) line profile at temperatures above 240K and poorly known frequencies previously introduced errors into the line shape analyses. The behavior of the HTP model was compared to the quadratic speed dependent Voigt profile (QSDVP) expressed in the frequency and time domains. A parameter uncertainty analysis was carried out using a Monte Carlo method based on the estimated pressure, transmittance and frequency measurement errors. From the analyses, the Pe(11) line strength was estimated to be 1.2014(50)×10−20 in cmmolecule−1 units at 296K with the standard deviation in parenthesis. For analyzing these data, we found that a reduced form of the HTP, equivalent to the QSDVP, was most appropriate because the additional parameters included in the full HTP were not well determined. As a supplement to this work, expressions for analytic derivatives and a lineshape fitting code written in Matlab for the HTP are available.

HIGH-RESOLUTION NEAR-INFRARED SPECTROSCOPY OF HD 100546. II. ANALYSIS OF VARIABLE ROVIBRATIONAL CO EMISSION LINES

We present observations of rovibrational CO in HD 100546 from four epochs spanning January 2003 through December 2010. We show that the equivalent widths of the CO lines vary during this time period with the v=1-0 CO lines brightening more than the UV fluoresced lines from the higher vibrational states. While the spectroastrometric signal of the hot band lines remains constant during this period, the spectroastrometric signal of the v=1--0 lines varies substantially. At all epochs, the spectroastrometric signals of the UV fluoresced lines are consistent with the signal one would expect from gas in an axisymmetric disk. In 2003, the spectroastrometric signal of the v=1-0 P26 line was symmetric and consistent with emission from an axisymmetric disk. However, in 2006, there was no spatial offset of the signal detected on the red side of the profile, and in 2010, the spectroastrometric offset was yet more strongly reduced toward zero velocity. A model is presented that can explain the evolution of the equivalent width of the v=1-0 P26 line and its spectroastrometric signal by adding to the system a compact source of CO emission that orbits the star near the inner edge of the disk. We hypothesize that such emission may arise from a circumplanetary disk orbiting a gas giant planet near the inner edge of the circumstellar disk. We discuss how this idea can be tested observationally and be distinguished from an alternative interpretation of random fluctuations in the disk emission.

CH2 b̃1B1−ã1A1 Band Origin at 1.20 μm

The origin band in the b̃(1)B(1)-ã(1)A(1) transition of CH(2) near 1.2 μm has been recorded at Doppler-limited resolution using diode laser transient absorption spectroscopy. The assignments of rotational transitions terminating in upper state levels with K(a) = 0 and 1, were confirmed by ground state combination differences and extensive optical-optical double resonance experiments. The assigned lines are embedded in a surprisingly dense spectral region, which includes a strong hot band, b̃(0,1,0) K(a) = 0 - ã(0,1,0) K(a) = 1 sub-band lines, with combination or overtone transitions in the ã(1)A(1) state likely responsible for the majority of unassigned transitions in this region. From measured line intensities and an estimate of the concentration of CH(2) in the sample, we find the transition moment square for the 0(00) ← 1(10) transition in the b̃(1)B(1)(0,0,0)(0)-ã(1)A(1)(0,0,0)(1) sub-band is 0.005(1) D(2). Prominent b̃(1)B(1)(0,1,0)(0)-ã(1)A(1)(0,1,0)(1) hot band lines were observed in the same spectral region. Comparison of the intensities of corresponding rotational transitions in the two bands suggests the hot band has an intrinsic strength approximately 28 times larger than the origin band. Perturbations of the excited state K(a) = 0 and 1 levels are observed and discussed. The new measurements will lead to improved future theoretical modeling and calculations of the Renner-Teller effect between the ã and b̃ states in CH(2).

The high-resolution far-infrared spectrum of methane at the SOLEIL synchrotron

As a tetrahedral molecule, methane has no permanent dipole moment. Its spectrum, however, displays faint absorption lines in the THz region, due to centrifugal distorsion effects. This is important for planetary applications since this region is used to measure methane concentration in some planetary atmospheres, in particular on Titan. Up to now, all measurements relied either on some old low resolution infrared absorption spectra, or on high resolution Stark measurements for low J values only. Even if these results have been reexamined recently [Wishnow EH, Orton GS, Ozier I, Gush HP. The distorsion dipole rotational spectrum of CH 4: a low temperature far-infrared study. J Quant Spectrosc Radiat Transfer 2007;103:102–17], it seemed highly desirable to obtain much more precise laboratory data. The high-intensity synchrotron radiation, combined with a 151.75±0.1 m optical path in a White cell and a Bruker IFS 125 HR FTIR spectrometer at the AILES beamline of SOLEIL, enabled us to record this very weak spectrum at high resolution for the first time. Spectra were obtained in the 50–500 cm −1 wavenumber range at 296 K and 9.91, 20, 50 and 100 mbar with a resolution of 0.00074, 0.00134, 0.0034 and 0.0067 cm −1 (FWHM of the sinc function), respectively. The rotational clusters are fully resolved and the good signal-to-noise ratio has enabled precise measurements of transition intensities (92 cold band lines and 96 Dyad–Dyad hot band lines, with normal abundance intensities in the range 2×10 −26–1×10 −24 cm −1/(mol cm −2)), yielding an accurate determination of the dipole moment derivatives. Such results should allow a better determination of CH 4 concentration in planetary objects.

Absorption by CS2 molecules on “hot” band emission lines from a TEA CO2 laser

We have measured absorption of emission from a TEA CO2 laser, lasing on hot band lines, in pure CS2 and a mixture of CS2 with air, and we have determined the optimal lines for optical excitation. Numerical modeling has shown that as the peak intensity of the pump radiation is increased, we observe absorption saturation, the extent of which decreases as the pressure increases. The major factor responsible for absorption saturation is the “rotational bottleneck” effect. Depending on the peak intensity of the radiation, addition of a buffer gas can lead to an increase or decrease in the absorption.

Global fit analysis including the ν9 + ν4 − ν4 hot band of ethane: Evidence of an interaction with the ν12 fundamental

The ν 9 fundamental band of ethane occurs in the 12 μm region. It is the strongest band of ethane in a terrestrial window and is commonly used for the identification of ethane in the Jovian planets. The ν 9 + ν 4 − ν 4 band occurs in the same region; neither can be analysed as an isolated band, since both are embedded in the torsional bath of the ground vibrational state. We report here two global fit models including data from both of these bands as well as the ν 3 fundamental and the ν 4, 2 ν 4 − ν 4, and 3 ν 4 torsional transitions. The first is restricted to −5 ⩽ KΔ K ⩽ 15 in the hot band and gives an excellent fit to the included data. Three resonant interactions are identified in this fit—a Coriolis interaction with two resonant cases between the ν 9 torsional stack and that of the ground vibrational state (gs) and a resonant Fermi interaction between the ν 3 fundamental and the gs. Hot band lines with KΔ K < −5 are influenced by a fourth perturbation, with a crossing at −11 < KΔ K < −10, which has been attributed to an interaction with the ν 12 fundamental. A second fit, demonstrating a promising treatment of this interaction, is also presented.

Water Production Rates, Rotational Temperatures, and Spin Temperatures in Comets C/1999 H1 (Lee), C/1999 S4, and C/2001 A2

Water hot-band lines were detected in comets C/1999 H1 (Lee), C/1999 S4 (LINEAR), and C/2001 A2 (LINEAR) in the 2.9 � m spectral region using high-dispersion (k=� k � 2 ; 10 4 ) infrared spectroscopy with NIRSPEC at the W. M. Keck Observatory. The density of H2O emissions in this spectral region, the spectral coverage and resolution of NIRSPEC, and fluorescence models developed for these hot bands enabled the determination of H2O production rates, rotational temperatures, and ortho-to-para ratios (OPRs) in these comets. Previous studies revealed clear diversity in the volatile organic chemistries of these comets, suggesting that they may have formed in different regions of the early solar nebula. The nuclear spin temperature of H2O as derived from its OPR is another possible indicator of cometary formation temperature and region. Nuclear spin temperatures for H2O were derived on one date in comet S4 and two dates in Lee and A2. Derived spin temperatures for H2O in these comets are � 30, 30 þ15 � 6 ,a nd 23 þ4 � 3 K for S4, Lee, and A2, respectively. Measurements are consistent with a possible link between nuclear spin temperatures and volatile abundances, but studies of more comets and continued improvements in water hot-band fluorescence models are needed to more stringently test this. Subject headingg comets: general — comets: individual (C/1999 S4, C/2001 A2, Lee (C/1999 H1)) — infrared: solar system — techniques: spectroscopic

Dual-mode CO2-laser/microwave-sideband spectrometer with broadband and saturation dip detection for CH3OH

This work reports dual-mode operation of a broadly tunable CO2-laser/microwave-sideband spectrometer employing a Cheo waveguide modulator and a CO2 laser that can operate on hot and sequence band lines as well as low- and high-J regular band lines. The spectrometer has a broadband scanning mode at Doppler-limited resolution for spectral searching and assignment, and a narrow-band sub-Doppler mode for precision measurements. In broadband mode, a 6.7–18.5 GHz (∼0.4 cm−1) window can be covered for each sideband in a single microwave sweep with a tracking Fabry–Perot etalon filter under computer control. In sub-Doppler mode, saturation-dip spectra are obtained at sub-MHz resolution with absolute frequency measurement accuracy of the order of ±200 kHz. The instrumental performance is demonstrated via spectra of the C–O stretching fundamental vibrational band of methanol. Doppler-limited broadband scans have been recorded with good signal-to-noise ratio in both the low- and high-J regions of the 9.6-μm-CO2 laser band, while narrow-band sub-Doppler scans have permitted clean separation of very close-lying lines in the CH3OH spectrum. The measurement precision is confirmed for several CH3OH transition systems through closure of combination loops. Our results illustrate the wide coverage and excellent resolution obtainable with CO2-sideband infrared laser radiation in a broadly tunable and convenient infrared source with high potential for spectroscopic applications.

Fourier transform spectra and torsion–rotation structure of the CO-stretching 2 ν8 overtone and 2 ν8– ν8 hot band of CH 3OH

The Fourier transform infrared (FTIR) spectrum of the 2 ν 8 overtone band of the CO-stretching vibrational mode of CH 3OH has been investigated in the 5-μm region at a spectral resolution of 0.0048 cm −1 (1/MOPD) and a higher pressure-path-length product than heretofore. Assignments are reported for high- K 2 ν 8 subbands in the ground state ( n=0) of the ν 12 torsion, and for 2ν 8+ν 12−ν 12 (n=1) and 2 ν 8+2 ν 12−2 ν 12 ( n=2) torsionally excited combination subbands. Upper-state υ 8=2 term values have been fitted to series expansions in powers of J( J+1) to obtain J-independent substate origins defining the torsion- K-rotation structure of the overtone state. Perturbations due to Coriolis and asymmetry resonances have been observed and characterized, as well as J-localized level-crossing resonances arising principally from interactions with the υ 7=2 overtone state of the in plane CH 3-rocking mode and the ( υ 7, υ 8)=(1,1) combination state. Differences between υ 8=2 and υ 8=1 term values have been used to generate a predicted map of the weak 2 ν 8– ν 8 CO-stretching hot band. The hot band underlies the main ν 8 fundamental in the 10-μm region, so is of significance to the determination of the fundamental line intensities. A number of the weak hot-band lines have been observed in the 10-μm FTIR spectrum.

Water production and release in Comet 153P/Ikeya–Zhang (C/2002 C1): accurate rotational temperature retrievals from hot-band lines near 2.9-μm

Multiple non-resonance fluorescence lines of water (H 2O) were detected in Comet 153/P Ikeya–Zhang (2002 C1) between UT 2002 March 21.9 ( R h =0.51 AU) and April 13.9 ( R h =0.78 AU), using the Cryogenic Echelle Spectrometer (CSHELL) at the NASA Infrared Telescope Facility. Analysis of 2.9-μm water lines enabled accurate determination of rotational temperatures on three dates. The derived H 2O rotational temperatures were 138 +6 −5, 141 +10 −9, and 94±3 K on UT 2002 March 22.0, March 23.0, and April 13.8, respectively. Water production rates were retrieved from spectral lines measured in nineteen separate grating settings over seven observing periods. The derived heliocentric dependence of the water production rate was Q=(9.2±1.1)×10 28[ R h (−3.21±0.26)] molecules s −1. The spatial distribution of H 2O in the coma was consistent with its release directly from the nucleus (as a native source) on all dates.

Precision Tunable Infrared Source at 10 μM: CO 2 -Laser/Microwave-Sideband System with an Evenson CO 2 Laser and a Cheo Waveguide Modulator

A CO2-laser/microwave-sideband tunable infrared source system has been newly built at the University of New Brunswick (UNB) in Canada. The system employs a high-resolution CO2 laser of Evenson design that lases on a wide range of lines including hot and sequence band lines as well as high-J lines of the regular 9.6 and 10.6 μm bands. The frequency of the CO2 laser is stabilized to the Lamb dip in the 4.3 μm fluorescence signal in an external CO2 cell. Microwave (MW) sidebands are generated in a Cheo-type infrared waveguide modulator driven by a synthesized sweeper and a traveling wave tube (TWT) amplifier. The MW sidebands appear on either side of the CO2 laser line, and are individually separated from the carrier by a tunable Fabry-Perot etalon. The sidebands currently have a typical power of about 1.4 mW and a continuous frequency tuning range of 22 GHz (from ± to ±18 GHz) when 5 W laser power and 15 W microwave power are delivered to the modulator. Details are given on the source construction and measured performance characteristics. Features of the source and its planned applications are discussed.

Optically Pumped Far-Infrared Laser Lines in Hydrazine, Methanol, Heavy Water, and Ammonia: New Laser Lines and Frequency Measurements,

A far-infrared laser cavity designed to favor short-wavelength laser lines was used to generate optically-pumped far-infrared laser radiation. New far-infrared laser lines were discovered in hydrazine, heavy water, ammonia, and several short-wavelength lines previously discovered in methanol were observed. Wavelength, frequency, and relative intensity measurements were performed on laser lines in the wavelength range 42.4 to 253.7 μm. Each far-infrared frequency measurement was obtained by mixing the far-infrared radiation with radiation from two reference CO2 lasers and from a microwave synthesizer in a metal-insulator-metal diode. The pump laser was a high-Q Fabry Perot resonator oscillating on 275 grating-selected laser lines including regular, sequence, and hot band lines.

C-13 Methanol Far-Infrared Laser: Newly Discovered Lines, Predictions, and Assignments

We report 25 new laser lines from 13CH3OH methanol when pumped by a cw CO2 laser. The majority of the lines are pumped by the 10R (regular) and 10SR (sequence) bands of the CO2 laser. Two are pumped by the 9HP(20) hot-band CO2 line. We measured 22 laser frequencies in this molecule, 19 from new lines and three from previously reported lines. We also remeasured and corrected the frequency of the 9P(44) pumped line as 3 378 404.87 MHz (88.738 μm). We assigned two lines-10SR(17), 77.5758 cm-1 and 10R(50), 119.3020 cm-1-and predicted other potential far-infrared laser lines with these two pumps. Copyright 1998 Academic Press.

A compact, highly stable CW CO2 laser without brewster windows

We describe an open resonator, quasi sealed-off; 70cm cavity length CO2 laser with very high stability of power and frequency, which lases on 96 lines from 9R42 (2W) to 10P52 (5W) with a power of >11W on 9R20, 9P20, 10R20 and 10P20, plus on 18 hotband lines with ≈2W. This laser was used successfully to pump an FIR ring laser [1] enabling an FIR power stability of ΔP/P ≈ 10−4 by use of a simple PI control loop, thus demonstrating its superb frequency stability.

The Hot Bands of Methane between 5 and 10 μm

Experimental line intensities of 1727 transitions arising from nine hot bands in the pentad–dyad system of methane are fitted to first and second order using the effective dipole moment expansion in the polyad scheme. The observed bands are ν3− ν2, ν3− ν4, ν1− ν2, ν1− ν4, 2ν4− ν4, ν2+ ν4− ν2, ν2+ ν4− ν4, 2ν2− ν2, and 2ν2− ν4, and the intensities are obtained from long-path spectra recorded with the Fourier transform spectrometer located at Kitt Peak National Observatory. For the second order model, some of the 27 intensity parameters are not linearly independent, and so two methods (extrapolation and effective parameters) are proposed to model the intensities of the hot bands. In order to obtain stable values for three of these parameters, 1206 dyad (ν4, ν2) intensities are refitted simultaneously with the hot band lines. The simultaneous fits to first and second order lead to rms values respectively of 21.5% and 5.0% for the 1727 hot band lines and 6.5% and 3.0% for the 1206 dyad lines. The band intensities of all 10 pentad–dyad hot bands are predicted in units of cm−2atm−1at 296 K to range from 0.931 (for 2ν4− ν4) to 7.67 × 10−5(for 2ν4− ν2). The total intensities are also estimated to first order for two other hot band systems (octad–pentad and tetradecad–octad) that give rise to weak transitions between 5 and 10 μm.

Spectroscopy of new CH3OH FIR laser lines pumped by new CO2 laser lines

The number of CO2 laser lines available for optical pumping of far-infrared (FIR) lasers has been significantly increased by the development of a new continuous wave (cw) CO2 laser at the Time and Frequency Division of the National Institute of Standards and Technology in Boulder, Colorado. This system operates on very high-J lines of the normal bands as well as on sequence and new hot-band lines, and has generated numerous new FIR laser transitions in CH3OH. These include the new 123 μm world-record holder, pumped by the 9HP(20) hot-band CO2 line, which is now the most efficient known FIR laser line. Assignments are given for a number of the IR pump – FIR laser energy level and transition systems, based on our high-resolution Fourier transform studies of the FIR and IR spectra of CH3OH. Features of the transition system for the 123 μm line and wave numbers for several further potential FIR laser lines are presented.

Improved Molecular Constants and Frequencies for the CO 2 Laser from New High- J Regular and Hot-Band Frequency Measurements

We dedicate this paper to the memory of F. R. Petersen, a pioneer in the field of laser frequency measurements. His meticulous attention to detail in the design and operation of the CO 2 laser and subsequent precise measurement of its transition frequencies led to his outstanding examples of stabilized laser frequency tables ( 1-3), which were the essential foundation for the present work. New frequencies are given for the 12C 16O 2, 13C 16O 2, 12C 18O 2, and 13C 18O 2 regular band laser transitions and for the hot-band transitions of 12 C 16O 2. These frequencies are based on a new least-squares analysis of all the frequency measurements of these four molecular species including new high- J measurements reported here and recent absolute frequency measurements. Fourteen new high- J transitions of the regular 12 C 16O 2 laser bands have been observed, the lasers have been stabilized with sub-Doppler saturated 4.3-μm fluorescence, and their frequencies have been measured. Nine of these transitions fill the gap between the 9.4- and 10.4-μm bands. Saturated 4.3-μm fluorescence also has been used to stabilize the 01 11[11 10,03 10] I and 01 11-[11 10,03 10] II hot-band laser lines. New frequency measurements are reported for 84 hot-band lines, which were also included in the reanalysis of the CO 2 laser transitions.