Minimal and complete set of descriptors for IR-absorption spectra of liquid H2–D2 mixtures

Robin Grössle,Alexander Kraus,Sebastian Mirz,Sebastian Wozniewski,Beate Bornschein

doi:10.1063/1.5111000

Abstract

The IR spectra of liquid hydrogen isotopologues (Q2 = H2, D2, T2, HD, HT, DT) are dominated by the interaction induced absorption. Therefore, the complexity tremendously increases with the number of different isotopologues in the sample. As we aim for a system independent calibration of IR absorption spectroscopy against all six isotopologues and three ortho–para ratios, we need a minimal and complete set of descriptors to predict the spectra and to decrease the needed calibration effort. For this, we grouped the absorption lines into three groups: absorption on monomers, phonons, and molecular dimers. In particular, molecular dimers contribute to the absolute number of absorption lines in the spectra of mixed isotopologues. To develop and test the set of descriptors, we make use of three spectra: a pure H2 sample, a pure D2 sample, and a mixed H2–D2 sample. We show a detailed analysis of these three spectra in the first and second vibrational branch in the range from 2000 cm−1 to 9000 cm−1. The set of descriptors found within this work can be used to identify and predict all lines in this range for liquid H2–D2mixtures.

Highlights

The development of analytic systems and methods for tritium and other hydrogen isotopologues is a main research field at the Tritium Laboratory Karlsruhe (TLK)
As we aim for a system independent calibration of IR absorption spectroscopy against all six isotopologues and three ortho–para ratios, we need a minimal and complete set of descriptors to predict the spectra and to decrease the needed calibration effort
We are aiming for a full calibration of the IR absorption spectra of liquid hydrogen isotopologue mixtures against all six concentrations (Q2 = H2, D2, T2, HD, HT, DT) and the three ortho/para ratios

Summary

Introduction

The development of analytic systems and methods for tritium and other hydrogen isotopologues is a main research field at the Tritium Laboratory Karlsruhe (TLK). Previous studies of absorption spectra of liquid H2 and D2 for different ortho/para ratios and temperatures show a strong influence of these parameters on the first vibrational branch.. Previous studies of absorption spectra of liquid H2 and D2 for different ortho/para ratios and temperatures show a strong influence of these parameters on the first vibrational branch.5,6 This limits the trueness of our calibration. For the interpretation of the experimental data, we aim for a minimal and complete set of descriptors for the IR spectra of liquid hydrogen isotopologue mixtures This will be crucial for the upcoming measurement campaigns with the tritium compatible setup that is under construction at the TLK, where we plan to extend this calibration to all six hydrogen isotopologues and variable ortho/para ratios. To extract the minimal and complete set of descriptors, we studied the IR absorption spectra of pure H2 and D2 liquid samples, and a H2–D2 mixture

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Discussion

Conclusion