Interference effects in the spectrum of HD: IV: the pure rotational band at room temperature

1986 ◽  
Vol 64 (3) ◽  
pp. 227-231 ◽  
Author(s):  
A. R. W. McKellar
Keyword(s):  
Spectral Resolution ◽  
Rotational Band ◽  
Path Length ◽  
Room Temperature ◽  
Dipole Transition ◽  
Rotational Spectrum ◽  
Density Range ◽  
Interference Effects ◽  
Fundamental Band ◽  
Line Strengths

The rotational spectrum of HD has been studied in absorption at room temperature for a density range of 6–57 amagat. Spectra were obtained in the 170- to 360-cm−1 region, including the R0(1), R0(2), and R0(3) transitions, with a 1-m path length and a spectral resolution varying from 0.05 to 0.20 cm−1. The observed line strengths were used to determine values for the dipole transition moments of HD in the range of 7.4 to 7.8 × 10−4 D, which is somewhat lower than currently accepted theoretical values of about 8.3–8.4 × 10−4 D. Only very small effects (≈0.2% per amagat) were found due to collisional interference on the line strengths; this result contrasts with much larger interference effects observed in the fundamental band, and it also casts some doubt on other recent studies of the rotational spectrum where larger interference effects were reported.

Further studies on the collision-induced absorption of the fundamental band of hydrogen at room temperature

1969 ◽  
Vol 47 (24) ◽  
pp. 2745-2751 ◽  
Author(s):  
G. Varghese ◽  
S. Paddi Reddy
Keyword(s):  
Binary Mixture ◽  
Infrared Absorption ◽  
Path Length ◽  
Room Temperature ◽  
Absorption Coefficients ◽  
Fundamental Band ◽  
Induced Absorption ◽  
Two Peaks

The collision-induced infrared absorption of the fundamental band of hydrogen in H2–O2 and H2–Xe mixtures was studied at room temperature at a path length of 105.2 cm at pressures up to 250 atm for different base pressures of hydrogen. The enhancement absorption profiles of the band in H2–O2 mixtures show the usual features of collision-induced absorption. However, the enhancement profiles in H2–Xe mixtures show some interesting new features. These are: the separation between the peaks of the two components of the Q branch remains almost constant with increasing density of the mixture; at all densities, the intensities of these two peaks are almost equal; and the lines of the quadrupolar branches O and S are more pronounced than those in any other binary mixture of hydrogen studied previously. Integrated absorption coefficients were measured for each of the mixtures and the binary and ternary absorption coefficients were derived. The values of the binary coefficients are 6.12 × 10−35 cm6 s−1 for H2–O2, and 11.34 × 10−35 cm6 s−1 for H2–Xe. The ternary coefficient is zero for H2–O2, whereas it has a large negative value for H2–Xe.

scholarly journals Pressure-induced infrared absorption of the fundamental band of hydrogen in H2–Ne and H2–Kr mixtures at room temperature

1968 ◽  
Vol 46 (12) ◽  
pp. 1373-1379 ◽  
Author(s):  
S. Paddi Reddy ◽  
W. F. Lee
Keyword(s):  
Infrared Absorption ◽  
Path Length ◽  
Room Temperature ◽  
Absorption Coefficients ◽  
Fundamental Band ◽  
Low Pressures

The pressure-induced infrared absorption of the fundamental band of hydrogen in H2–Ne and H2–Kr mixtures was studied at room temperature at a path length of 25.8 cm at pressures up to 400 atmospheres for different base pressures of hydrogen. In the enhancement absorption profiles of the band in H2–Ne mixtures, the S(1) line at all pressures and the QP component at low pressures show doublet structures. In the enhancement contours in H2–Kr mixtures, there is an indication of the QQ component between the QP and QR maxima at higher pressures, and the O and S lines are much stronger than the corresponding lines in H2–Ne mixtures. Integrated absorption coefficients were measured for each of the mixtures studied, and the binary and ternary absorption coefficients were derived. The values of the binary coefficients are 2.37 × 10−35 cm6 s−1 for H2–Ne and 7.56 × 10−35 cm6 s−1 for H2–Kr.

Interference effects in the spectrum of HD: VI: HD–HD, and HD–Kr at room temperature

1994 ◽  
Vol 72 (5-6) ◽  
pp. 215-224 ◽  
Author(s):  
A. R. W. McKellar
Keyword(s):  
Absorption Spectrum ◽  
Fourier Transform ◽  
High Resolution ◽  
Room Temperature ◽  
Dipole Transition ◽  
Interference Effects ◽  
Hydrogen Deuteride ◽  
Interference Phenomenon ◽  
Infrared Spectrometer ◽  
Line Positions

The absorption spectrum of the fundamental band of hydrogen deuteride (λ ≈ 2.7 μm) has been studied in pure HD and in mixtures with krypton at moderate densities (1–45 amagat) and room temperature, using a high-resolution Fourier transform infrared spectrometer. The effects that arise from interference between the allowed dipole transition moments of free HD and the dipoles induced during collisions were studied. For HD–HD collisions, the eight transitions from P1(3) to R1(4) were analyzed to determine line positions, intensities, shift and broadening coefficients, and the phase shift parameters that govern the interference effects. Thus the interference phenomenon was studied over a wider range of initial- and final-J values than previously possible, and the systematic dependence of the phase shifts on transition was determined. For HD–Kr collisions, the R1(0) and R1(1) transitions were examined in detail. The spectrum in the region of R1(1) exhibited a realtively broad underlying "plateau" feature that was shown to be due to the presence of impurity CF4 molecules in the Kr sample.

Interference effects in the spectrum of HD: III. The pure rotational band at 77 K for HD and HD–Ne mixtures

1984 ◽  
Vol 62 (12) ◽  
pp. 1673-1679 ◽  
Author(s):  
A. R. W. McKellar ◽  
J. W. C. Johns ◽  
W. Majewski ◽  
N. H. Rich
Keyword(s):  
Dipole Moment ◽  
Rotational Band ◽  
Reasonable Agreement ◽  
Permanent Dipole Moment ◽  
Destructive Interference ◽  
Interference Effects ◽  
Constructive Interference ◽  
Fundamental Band ◽  
A Value

The pure rotational R(0) transition of HD has been studied in pure HD and in HD–Ne mixtures at a temperature of 77 K and at densities between 3 and 123 amagat. Limited measurements of R(1) in pure HD were also made. A value of 8.18 ± 0.26 D was obtained for the R(0) permanent dipole moment of HD, in reasonable agreement with the theoretical value of 8.3 D. However, no evidence for destructive collisional interference effects at high densities was found, and in fact a slight constructive interference was noted. Thus, these results stand in contrast with those for the fundamental band, and with other recent experiments on the pure rotational band, in which destructive interference was invariably measured.

scholarly journals Broad-band high-resolution rotational spectroscopy for laboratory astrophysics

2019 ◽  
Vol 626 ◽  
pp. A34 ◽  
Author(s):  
J. Cernicharo ◽  
J. D. Gallego ◽  
J. A. López-Pérez ◽  
F. Tercero ◽  
I. Tanarro ◽  
...  
Keyword(s):  
Spectral Resolution ◽  
Accurate Determination ◽  
Broad Band ◽  
Laboratory Astrophysics ◽  
High Spectral Resolution ◽  
Rotational Spectroscopy ◽  
Rotational Spectrum ◽  
Vibrationally Excited ◽  
Radio Receivers ◽  
Cold Plasmas

We present a new experimental set-up devoted to the study of gas phase molecules and processes using broad-band high spectral resolution rotational spectroscopy. A reactor chamber is equipped with radio receivers similar to those used by radio astronomers to search for molecular emission in space. The whole range of the Q (31.5–50 GHz) and W bands (72–116.5 GHz) is available for rotational spectroscopy observations. The receivers are equipped with 16 × 2.5 GHz fast Fourier transform spectrometers with a spectral resolution of 38.14 kHz allowing the simultaneous observation of the complete Q band and one-third of the W band. The whole W band can be observed in three settings in which the Q band is always observed. Species such as CH3CN, OCS, and SO2 are detected, together with many of their isotopologues and vibrationally excited states, in very short observing times. The system permits automatic overnight observations, and integration times as long as 2.4 × 105 s have been reached. The chamber is equipped with a radiofrequency source to produce cold plasmas, and with four ultraviolet lamps to study photochemical processes. Plasmas of CH4, N2, CH3CN, NH3, O2, and H2, among other species, have been generated and the molecular products easily identified by the rotational spectrum, and via mass spectrometry and optical spectroscopy. Finally, the rotational spectrum of the lowest energy conformer of CH3CH2NHCHO (N-ethylformamide), a molecule previously characterized in microwave rotational spectroscopy, has been measured up to 116.5 GHz, allowing the accurate determination of its rotational and distortion constants and its search in space.

scholarly journals CryoSAXS as a Method for Measuring Low Resolution Macromolecular Structure

2014 ◽  
Vol 70 (a1) ◽  
pp. C408-C408
Author(s):  
Jesse Hopkins ◽  
Andrea Katz ◽  
Stephen Meisburger ◽  
Matthew Warkentin ◽  
Richard Gillilan ◽  
...  
Keyword(s):  
Radiation Damage ◽  
Path Length ◽  
Room Temperature ◽  
Structural Information ◽  
Total Sample ◽  
Free Variable ◽  
Low Resolution ◽  
X Ray ◽  
Atomic Structures ◽  
Fixed Path

Small angle X-ray scattering (SAXS) is an increasingly popular technique for obtaining low resolution structural information from macromolecules and complexes in solution. Biomolecular SAXS signals can rapidly degrade due to radiation damage, so that flow or oscillating cells and large total sample volumes may be required. For particularly sensitive or hard to produce samples, such as of light sensitive proteins, metalloenzymes, and large complexes, and studies where multiple buffer conditions are probed sample consumption may be prohibitive. We describe cryo-cooling of samples to 100 K to prevent X-ray induced radiation damage. We identify SAXS-friendly cryoprotectant conditions that suppress ice formation upon cooling, and compare cryoSAXS profiles obtained in window-free variable-path-length cells with room temperature measurements for a variety of standard molecules. We obtain data sufficient for envelope reconstructions using scattering volumes as small as 20 nL, and find good agreement between cryoSAXS data and known atomic structures. We also discuss work on developing low-volume fixed path-length sample holders for cryoSAXS. Cryo-cooled samples can withstand doses that are 2-3 orders of magnitude higher than typically used for SAXS at room temperature, comparable to those used in cryo-crystallography. While practical challenges remain, cryoSAXS opens the possibility of studies exploiting high brightness X-ray sources and mail-in high-throughput SAXS. This work is funded by the NSF (DBI-1152348).

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