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Title: Magnetic Trapping and Zeeman Relaxation of NH (X {sup 3}{sigma}{sup -})

Abstract

NH radicals are magnetically trapped and their Zeeman relaxation and energy transport collision cross sections with helium are measured. Continuous buffer-gas loading of the trap is direct from a room-temperature molecular beam. The Zeeman relaxation (inelastic) cross section of magnetically trapped electronic, vibrational, and rotational ground state NH molecules in collisions with {sup 3}He is measured to be 3.8{+-}1.1x10{sup -19} cm{sup 2} at 710 mK. The NH-He energy transport cross section is also measured, indicating a ratio of diffusive to inelastic cross sections of {gamma}=7x10{sup 4}, in agreement with recent theory [R. V. Krems, H. R. Sadeghpour, A. Dalgarno, D. Zgid, J. Klos, and G. Chalasinski, Phys. Rev. A 68, 051401 (2003)].

Authors:
; ;  [1];  [2];  [3];  [2];  [4];  [2]
  1. Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States)
  2. (United States)
  3. Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 (United States)
  4. Harvard-MIT Center for Ultracold Atoms, Cambridge, Massachusetts 02138 (United States)
Publication Date:
OSTI Identifier:
20951396
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 98; Journal Issue: 21; Other Information: DOI: 10.1103/PhysRevLett.98.213001; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; CROSS SECTIONS; GROUND STATES; HELIUM; HELIUM 3; MOLECULAR BEAMS; RELAXATION; TEMPERATURE RANGE 0273-0400 K; TRAPPING; TRAPS; ZEEMAN EFFECT

Citation Formats

Campbell, Wesley C., Tsikata, Edem, Buuren, Laurens D. van, Harvard-MIT Center for Ultracold Atoms, Cambridge, Massachusetts 02138, Lu, H.-I, Harvard-MIT Center for Ultracold Atoms, Cambridge, Massachusetts 02138, Doyle, John M., and Department of Physics, Harvard University, Cambridge, Massachusetts 02138. Magnetic Trapping and Zeeman Relaxation of NH (X {sup 3}{sigma}{sup -}). United States: N. p., 2007. Web. doi:10.1103/PHYSREVLETT.98.213001.
Campbell, Wesley C., Tsikata, Edem, Buuren, Laurens D. van, Harvard-MIT Center for Ultracold Atoms, Cambridge, Massachusetts 02138, Lu, H.-I, Harvard-MIT Center for Ultracold Atoms, Cambridge, Massachusetts 02138, Doyle, John M., & Department of Physics, Harvard University, Cambridge, Massachusetts 02138. Magnetic Trapping and Zeeman Relaxation of NH (X {sup 3}{sigma}{sup -}). United States. doi:10.1103/PHYSREVLETT.98.213001.
Campbell, Wesley C., Tsikata, Edem, Buuren, Laurens D. van, Harvard-MIT Center for Ultracold Atoms, Cambridge, Massachusetts 02138, Lu, H.-I, Harvard-MIT Center for Ultracold Atoms, Cambridge, Massachusetts 02138, Doyle, John M., and Department of Physics, Harvard University, Cambridge, Massachusetts 02138. Fri . "Magnetic Trapping and Zeeman Relaxation of NH (X {sup 3}{sigma}{sup -})". United States. doi:10.1103/PHYSREVLETT.98.213001.
@article{osti_20951396,
title = {Magnetic Trapping and Zeeman Relaxation of NH (X {sup 3}{sigma}{sup -})},
author = {Campbell, Wesley C. and Tsikata, Edem and Buuren, Laurens D. van and Harvard-MIT Center for Ultracold Atoms, Cambridge, Massachusetts 02138 and Lu, H.-I and Harvard-MIT Center for Ultracold Atoms, Cambridge, Massachusetts 02138 and Doyle, John M. and Department of Physics, Harvard University, Cambridge, Massachusetts 02138},
abstractNote = {NH radicals are magnetically trapped and their Zeeman relaxation and energy transport collision cross sections with helium are measured. Continuous buffer-gas loading of the trap is direct from a room-temperature molecular beam. The Zeeman relaxation (inelastic) cross section of magnetically trapped electronic, vibrational, and rotational ground state NH molecules in collisions with {sup 3}He is measured to be 3.8{+-}1.1x10{sup -19} cm{sup 2} at 710 mK. The NH-He energy transport cross section is also measured, indicating a ratio of diffusive to inelastic cross sections of {gamma}=7x10{sup 4}, in agreement with recent theory [R. V. Krems, H. R. Sadeghpour, A. Dalgarno, D. Zgid, J. Klos, and G. Chalasinski, Phys. Rev. A 68, 051401 (2003)].},
doi = {10.1103/PHYSREVLETT.98.213001},
journal = {Physical Review Letters},
number = 21,
volume = 98,
place = {United States},
year = {Fri May 25 00:00:00 EDT 2007},
month = {Fri May 25 00:00:00 EDT 2007}
}
  • The rate coefficient of the reaction NH(X {sup 3}{sigma}{sup -})+D({sup 2}S){yields}{sup k{sub 1}}products (1) is determined in a quasistatic laser-flash photolysis, laser-induced fluorescence system at low pressures. The NH(X) radicals are produced by quenching of NH(a {sup 1}{delta}) (obtained in the photolysis of HN{sub 3}) with Xe and the D atoms are generated in a D{sub 2}/He microwave discharge. The NH(X) concentration profile is measured in the presence of a large excess of D atoms. The room-temperature rate coefficient is determined to be k{sub 1}=(3.9{+-}1.5)x10{sup 13} cm{sup 3} mol{sup -1} s{sup -1}. The rate coefficient k{sub 1} is the summore » of the two rate coefficients, k{sub 1a} and k{sub 1b}, which correspond to the reactions NH(X {sup 3}{sigma}{sup -})+D({sup 2}S){yields}{sup k{sub 1a}}ND(X {sup 3}{sigma}{sup -})+H({sup 2}S) (1a) and NH(X {sup 3}{sigma}{sup -})+D({sup 2}S){yields}{sup k{sub 1b}}N({sup 4}S)+HD(X {sup 1}{sigma}{sub g}{sup +}) (1b), respectively. The first reaction proceeds via the {sup 2}A{sup ''} ground state of NH{sub 2} whereas the second one proceeds in the {sup 4}A{sup ''} state. A global potential energy surface is constructed for the {sup 2}A{sup ''} state using the internally contracted multireference configuration interaction method and the augmented correlation consistent polarized valence quadrupte zeta atomic basis. This potential energy surface is used in classical trajectory calculations to determine k{sub 1a}. Similar trajectory calculations are performed for reaction (1b) employing a previously calculated potential for the {sup 4}A{sup ''} state. The calculated room-temperature rate coefficient is k{sub 1}=4.1x10{sup 13} cm{sup 3} mol{sup -1} s{sup -1} with k{sub 1a}=4.0x10{sup 13} cm{sup 3} mol{sup -1} s{sup -1} and k{sub 1b}=9.1x10{sup 11} cm{sup 3} mol{sup -1} s{sup -1}. The theoretically determined k{sub 1} shows a very weak positive temperature dependence in the range 250{<=}T/K{<=}1000. Despite the deep potential well, the exchange reaction on the {sup 2}A{sup ''} ground-state potential energy surface is not statistical.« less
  • We present a theoretical study of the Zeeman relaxation of the magnetically trappable lowest field seeking state of MnH ({sup 7{Sigma}}) in collisions with {sup 3}He. We analyze the collisional Zeeman transition mechanism as a function of the final diatomic state and its variation as a function of an applied magnetic field. We show that as a result of this mechanism the levels with {Delta}M{sub j}>2 give negligible contributions to the Zeemam relaxation cross section. We also compare our results to the experimental cross sections obtained from the buffer-gas cooling and magnetic trapping of this molecule and investigate the dependencemore » of the Zeeman relaxation cross section on the accuracy of the three-body interaction at ultralow energies.« less
  • The rate constant for the reactions NH{sub 2}({sub x}{sup 2}B{sub 1}) + NH(X{sup 3}{Sigma}{sup -}) and NH{sub 2}({sub x}{sup 2}B{sub 1}) + H({sup 2}S) were measured over a pressure range from 2 to 10 Torr in CF{sub 4}, or Ar gases at 293 {+-} 2 K. The radicals were produced by the 193 nm photolysis of NH{sub 3} dilute in the carrier gas. Both radicals were monitored simultaneously following the photolysis laser pulse using high-resolution time-resolved absorption spectroscopy. The NH{sub 2} radical was monitored using the {sup 1}2{sub 21} {l_arrow} {sup 1}3{sub 31} rotational transition of the (0,7,0){sub A}{sup 2}A{submore » 1} {l_arrow} (0,0,0) {sub x}{sup 2}B{sub 1} vibronic band near 675 nm, and the NH radical was monitored using the {sup 1}R{sub 3}(4) rotational transition on the 1?0 vibrational transition near 3084 nm. The data was analyzed using model simulations of the NH{sub 2} and NH temporal concentration profiles. The rate constants for the NH{sub 2} + NH and NH{sub 2} + H reactions were found to be (9.6 {+-} 3.2) x 10{sup -11} and (7.7 {+-} 14) x 10{sup -15} cm{sup 3} molecule{sup -1} s{sup -1}, respectively, where the uncertainty includes an estimate of both systematic and random errors. The measurements were independent of the nature of the diluents, CF{sub 4} or Ar, and total pressure.« less
  • The direct hydrogen abstraction mechanisms on {sup 3}A{double{underscore}prime} potential surfaces for the reactions of NH({sup 3{Sigma}{sup {minus}}}) with CH{sub 4}, CH{sub 3}F, CH{sub 2}F{sub 2}, and CHF{sub 3} have been studied systematically using ab initio molecular orbital theory. The G2(MP2) calculations reveal that all reactions involve significant energy barriers. The effect of fluorine substitution was examined. The NH + CHF{sub 3} reaction was found to possess the highest barrier among the four reactions. The barriers for both NH + CH{sub 3}F and NH + CH{sub 2}F{sub 2} reactions are about 2 kcal/mol lower than that for the NH + CH{submore » 4} reaction. The rate constants for the four reactions have been deduced using transition-state theory with asymmetric Eckart tunneling correction and hindered rotor approximation over the temperature range 200--3000 K. The following least-squares-fitted expressions for the rate constants were obtained: {kappa}{sup H}{sub 1}(NH+CH{sub 4}) = (9.41 x 10{sup {minus}18})T{sup 2.28} e{sup {minus}10233/T}, {kappa}{sup H}{sub 2}(NH+CH{sub 3}F) = (1.69 x 10{sup {minus}18})T{sup 2.31} e{sup {minus}9217/T}, {kappa}{sup H}{sub 3}(NH+CH{sub 2}F{sub 2}) = (1.52 x 10{sup {minus}18})T{sup 2.32} e{sup {minus}9080/T}, {kappa}{sup H}{sub 4}(NH+CHF{sub 3}) = (2.12 x 10{sup {minus}18})T{sup 2.29} e{sup {minus}10750/T}, in cm{sup 3}molecule{sup {minus}1} s{sup {minus}1}. The deuterium kinetic isotope effects have also been investigated. All reactions show the significant and normal kinetic isotope effects.« less
  • The reaction of the cyano radical (CN) with methane was studied by time-resolved infrared absorption spectroscopy by monitoring individual rovibrational states of the HCN and CH{sub 3} products. The initial vibrational level distribution of the bendless vibrational levels of HCN({ital v}{sub 1},0,{ital v}{sub 3}) was determined by plotting the time dependence of the fractional population of a vibrational level and extrapolating these curves to the origin of time. About 20{percent} of the HCN products were observed to be initially produced in the HCN({ital v}{sub 1},0,{ital v}{sub 3}) vibrational levels, with {ital v}{sub 1} and {ital v}{sub 3}=0,1,2. The CN radicalmore » was created by laser photolysis of three different precursors. Each photolyte provided a different initial vibrational level distribution of CN; however, similar initial HCN({ital v}{sub 1},0,{ital v}{sub 3}) vibrational level distributions were obtained independent of the CN radical precursor. This may indicate that the CN radical does not act as a spectator bond during the course of a reactive encounter for this system. The time dependence of the CH{sub 3} (000{sup 0}0) ground state was also followed using time-resolved infrared absorption spectroscopy. Preliminary data indicates that a large fraction, if not all, the CH{sub 3} radicals are produced in their ground state in the title reaction. {copyright} {ital 1996 American Institute of Physics.}« less