Infrared emission spectroscopy of NH: Comparison of a cryogenic echelle spectrograph with a Fourier transform spectrometer

Abstract

The high-resolution emission spectrum of NH has been observed in the near infrared using a Fourier transform spectrometer ͑FTS͒ and a cryogenic echelle spectrograph ͑called Phoenix͒ at the National Solar Observatory at Kitt Peak. By using a large format InSb array detector, the newly constructed Phoenix is calculated to offer a large increase in sensitivity over a Fourier transform spectrometer for measurements near 5 m ͑2000 cm Ϫ1 ͒. In order to test the performance of Phoenix, we recorded vibration-rotation emission spectra of the free-radical NH. The infrared bands of NH were produced in a microwave discharge of a mixture of NH 3 and He. The rotational structure of five bands, 1-0, 2-1, 3-2, 4-3, and 5-4 in the 2200-3500 cm Ϫ1 region has also been measured using two FTS spectra. An analysis of these bands combined with the previous electronic, vibrationrotation, and pure rotation measurements provides improved molecular constants for the ground electronic state. In particular, we have extended the range of measured J values so that the new constants are suitable for predicting line positions in high-temperature sources such as stellar atmospheres and flames. A comparison of the Phoenix spectra with the FTS spectra confirms the higher sensitivity of the Phoenix spectrometer. The relative advantages and disadvantages of instruments like Phoenix are discussed. Although designed for astronomical work, cryogenic echelle spectrographs have applications in the ultrasensitive detection of molecules in chemical physics.

Spectroscopic study of the 14NH radical in vibrationally excited levels of the X3Σ− state by far infrared laser magnetic resonance

“…This has allowed the determination of an accurate set of parameters in the effective Hamiltonian. These vibration-rotation levels have been studied previously through electronic spectroscopy [2] and most recently (and accurately) through its infrared spectrum [20]. The rotational and fine-structure parameters determined in the latter study are compared with those of the present work in Table 4.…”

“…For example, an accurate set of experimentally determined molecular parameters for 15 NH would permit the relative abundances of 14 N and 15 N to be determined in regions of star formation, providing information on this process. 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 [20] in the least-squares fit. d The axial dipolar interaction c is related to the hyperfine t parameter by t = c 3 [35].…”

“…Each data point was weighted as the inverse square of its experimental uncertainty, that is based on the uncertainty in the magnetic field, the tuning rate and the uncertainty in the farinfrared laser frequency. Because our measurements are confined to low N-values, we have constrained the centrifugal distortion parameters Hv and Dv to the values determined in a recent infrared study [20]. In addition, the 14 N electric quadrupole interaction had a marginal effect on the spectra; this parameter was therefore constrained to the value determined recently for the v = 0 level [27].…”

“…This study recorded the vibrational fundamental of the X 3 ground state. Recently this work has been extended by the investigation of the first five vibration-rotation bands in the v = 1 sequence [20]. In 1985 Hall et al [21] observed the vibrational fundamental of the excited a 1 state by colour centre laser kinetic spectroscopy.…”

Time-Domain Measurement of Spontaneous Vibrational Decay of Magnetically Trapped NH

“…Taking ! 3092:88 cm ÿ1 from spectroscopic constants in the literature [23,24] gives us a measured value of j 10 j 0:0540 0:0009 ÿ0:0018 D. Comparison of our experimental value of rad;exp : to theory is crucial to claim resolution of the conflicting published measured and theoretical values. To obtain a state-of-the-art calculated value we perform an ab initio calculation of the spontaneous emission lifetime of NHv 1.…”