observed. From the near-infrared spectrum, we determined an ortho-to-para ratio, the rotational and vibrational excitation temperatures, and the dominant excitation mechanism of the 2 for many objects surveyed. One unexpected result from this analysis is that the 2 is excited by absorption of ultraviolet photons in most of the PNe surveyed, although for several PNe in our survey collisional excitation in moderate velocity shocks plays an important role. The correlation between bipolar morphology and 2emission has been strengthened with the new detections of 2 in this survey. We discuss the role of winds and photons to the excitation of 2 in PNe, and consider some implications to the utility of 2 as a nebular diagnostic and to our understanding of PNe structure and evolution.
author:
- 'Joseph L. Hora'
- 'William B. Latter'
- 'Lynne K. Deutsch'
title: |
    Investigating the Near-Infrared Properties of Planetary Nebulae\
    II. Medium Resolution Spectra
---

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Introduction
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This is the second of two papers describing the results of surveys examining the properties of planetary nebulae (PNe) as observed in the near-infrared ($\lambda = 1 - 2.5$ ). The first paper 