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A modified dual-slope method for heat capacity measurements of condensable gases (2000)

Pilla, S. ; Hamida, J. A. ; Sullivan, N. S.

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 71 (2000), S. 3841-3845

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ISSN: 1089-7623

Source: AIP Digital Archive

Topics: Physics , Electrical Engineering, Measurement and Control Technology

Notes: A high resolution nonadiabatic method for measuring the heat capacity (CP) of bulk samples of condensable gases in the range of 7.5–70 K is described. In this method CP is evaluated by directly comparing the heating and cooling rates of the sample temperature for two algebraically independent heat pulse sequences without explicit use of the thermal conductance between sample and thermal bath. A fully automated calorimeter for rapid measurement of CP of molecular solids utilizing this technique is presented. The technique along with the automated calorimeter with a provision to apply external electric and magnetic fields is particularly useful for the study of continuous phase transitions in molecular solids as well as field induced changes in the heat capacity. © 2000 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.1290040

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The Orientational Ordering of Molecular Hydrogen in 2D (2000)

Sullivan, N. S. ; Kim, K.

Springer

Journal of low temperature physics 120 (2000), S. 89-106

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ISSN: 1573-7357

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract The orientational ordering of ortho-hydrogen molecules on a triangular lattice is calculated as a function of ortho concentration using the method of restricted traces. The calculated temperatures for the transitions from the disordered phase to the long range pinwheel ordered phase show a strong concentration dependence with a critical concentration X c=73% below which the long range ordering is not realized in this model. The results are consistent with recent NMR studies of ortho-para hydrogen mixtures adsorbed as a commensurate $$\sqrt 3 $$ × $$\sqrt 3 $$ structure on hexagonal boron nitride for which X c=69±4%. The values of the observed transition temperatures can only be understood if there is a large renormalization of the effective quadrupolar interaction constant in 2D.