Nuclear spin state relaxation in formaldehyde: dependence of the rate constant on pressure

Peters, Gwm Gerrit; Schramm, B.

doi:10.1016/s0009-2614(99)00042-1

Cited by 34 publications

(34 citation statements)

References 9 publications

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“…It implies that the conversion by direct process is too slow to be taken into account for the formaldehyde conversion. In fact, the authors [4] had arrived at the same conclusion.…”

Section: Direct and Indirect Conversion Mechanismsmentioning

confidence: 70%

“…This mechanism is responsible for the hydrogen isomer conversion by paramagnetic O 2 [9]. It is important for us that the hydrogen conversion induced by O 2 (the rate is equal to 8 · 10 −6 s −1 /Torr [2]) appears to be much slower than the spin conversion in formaldehyde [4],…”

Section: Direct and Indirect Conversion Mechanismsmentioning

confidence: 99%

“…In notations of [4] this rate is equal to k 1 + k 2 , where k 1 and k 2 are the ortho-to-para and para-to-ortho conversion rates, respectively.…”

Section: Direct and Indirect Conversion Mechanismsmentioning

confidence: 99%

“…An experimental arrangement in [4] corresponds to "nonmagnetic" collision partner having a magnetic moment on the order of nuclear magneton, µ n , thus by 10 3 times smaller. The conversion rate by direct mechanism depends on magnetic moment as µ 2 [10].…”

Section: Direct and Indirect Conversion Mechanismsmentioning

confidence: 99%

“…But it is worthwhile to perform new analysis in order to account new important information. First, the formaldehyde spin conversion was recently investigated experimentally and the gas phase conversion rate was measured for the first time [4]. Second, formaldehyde molecular structure and molecular spectroscopic parameters have been determined very accurately [5][6][7].…”

Section: Introductionmentioning

confidence: 99%

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Nuclear spin conversion in formaldehyde

Chapovsky¹

2001

Journal of Molecular Structure

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Theoretical model of the nuclear spin conversion in formaldehyde (H 2 CO) has been developed. The conversion is governed by the intramolecular spinrotation mixing of molecular ortho and para states. The rate of conversion has been found equal γ/P = 1.4 · 10 −4 s −1 /Torr. Temperature dependence of the spin conversion has been predicted to be weak in the wide temperature range T = 200 − 900 K.

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“…It implies that the conversion by direct process is too slow to be taken into account for the formaldehyde conversion. In fact, the authors [4] had arrived at the same conclusion.…”

Section: Direct and Indirect Conversion Mechanismsmentioning

confidence: 70%

Section: Direct and Indirect Conversion Mechanismsmentioning

confidence: 99%

“…In notations of [4] this rate is equal to k 1 + k 2 , where k 1 and k 2 are the ortho-to-para and para-to-ortho conversion rates, respectively.…”

Section: Direct and Indirect Conversion Mechanismsmentioning

confidence: 99%

Section: Direct and Indirect Conversion Mechanismsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Nuclear spin conversion in formaldehyde

Chapovsky¹

2001

Journal of Molecular Structure

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Comparative study of degenerate four‐wave mixing and cavity ringdown signal intensities of formaldehyde in a molecular beam

Tulej¹,

Meisinger²,

Knopp³

et al. 2006

J Raman Spectroscopy

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A comparison of degenerate four-wave mixing (DFWM) and cavity ring-down (CRD) spectroscopy is made on jet-cooled formaldehyde under identical expansion conditions. We show that both methods are applicable to the low-density environment of a molecular beam. However, a slightly superior signalto-noise ratio for the background-free DFWM method is observed for our experimental configurations. Absorption spectra simulated by applying an asymmetric rotor model are used to deduce Boltzmann temperatures of the rotational population distribution by a nonlinear least-squares fit to the experimental data. In addition, partial interconversion of the nuclear spin upon supersonic expansion is observed. Consequently, a second fit parameter, describing the para/ortho concentration ratio in the molecular beam, is introduced. The resulting simulated spectra are in favorable agreement with the relative CRD intensities. A simple model for the reduction of the DFWM signal intensities to population is applied yielding absorption-like spectra in accordance with both the simulations and the CRD measurements. We conclude that DFWM spectroscopy is applicable to deduce population distributions of an asymmetric rotor molecule under free-jet conditions.

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