ABSTRACT
This paper presents a statistical evaluation of the responsivity data on a number of heat-flux sensors, calibrated using an electrical substitution radiometer as a transfer standard up to 5 W·cm(-2). The sensors, furnished by the customers, were of circular-foil or thermopile type. Comparison of the NIST and the customer measured responsivity values showed that the measurements agree within 3 % for more than half the number of sensors tested, so far. Considering the variation in the customer calibration techniques and the wide measuring range of the sensors used in the calibration, the agreement is encouraging.
ABSTRACT
A global fit of microwave and millimeter-wave rotational transitions in the ground and first excited torsional states (v(t) = 0 and 1) of acetic acid (CH(3)COOH) is reported, which combines older measurements from the literature with new measurements from Kharkov, Lille, and NIST. The fit uses a model developed initially for acetaldehyde and methanol-type internal rotor molecules. It requires 34 parameters to achieve a unitless weighted standard deviation of 0.84 for a total of 2518 data and includes A- and E-species transitions with J
ABSTRACT
We report what we believe to be the first systematic study of Doppler-free, nonlinear absorption by use of cavity ringdown spectroscopy. We have developed a variant of cavity ringdown spectroscopy for the mid-infrared region between 9 and 11 microm, exploiting the intracavity power buildup that is possible with continuous-wave lasers. The infrared source consists of a continuous-wave CO2 laser with 1-mW tunable infrared sidebands that couple into a high-finesse stable resonator. We tune the sideband frequencies to observe a saturated, Doppler-free Lamb dip in the nu7, 11(1,10) <-- 11(2,10) rovibrational transition of ethylene (C2H4). Power studies of the Lamb dip are presented to examine the intracavity effects of saturation on the Lamb-dip linewidth, the peak depth, and the broadband absorption.
ABSTRACT
We measured at 296 K the rotational line strengths and pressure-broadening coefficients for the 1.27-mum, a (1)D(g)-X (3)?(g)(-), v = 0-0 band of O(2) with a Fourier transform infrared spectrometer using an optical path length of 84 m, a spectral resolution of 0.01 cm(-1), and sample pressures between 13 and 104 kPa. The integrated band strength is 7.79(17) x 10(-6) m(-2) Pa(-1) [7.89(17) x 10(-5) cm(-2) atm(-1)], and the Einstein Acoefficient for spontaneous emission is 2.237(51) x 10(-4) s(-1), which corresponds to an upper-state1/e lifetime of 1.24(3) h. The pressure-broadening coefficients decrease with increasing N and range from 19 to 38 MHz/kPa (FWHM). The mean value for the transitions studied is 30.3(21) MHz/kPa [0.1024(71) cm(-1)/atm] (FWHM). The Einstein A coefficient determined here is in good agreement with the widely accepted value of 2.58 x 10(-4) s(-1) initially obtained by Badgeret al. [J. Chem. Phys. 43, 4345 (1965)] more than 30 years ago. The standard uncertainties given above are one standard deviation.
ABSTRACT
Spectroscopic characterizations of the stereochemistry of complexes of ammonia (NH(3)) have strongly confirmed some long-held ideas about the weak interactions of NH(3) while casting doubt on others. As expected, NH(3) is observed to be a nearly universal proton acceptor, accepting hydrogen bonds from even some of the weakest proton donors. Surprisingly, no evidence has been found to support the view that NH(3) acts as a proton donor through hydrogen bonding. A critical evaluation of the work that has been done to gather such evidence, as well as of earlier work involving condensed-phase observations, suggests that NH(3) might well be best described as a powerful hydrogen-bond acceptor with little propensity to donate hydrogen bonds.
