**Previous
abstract** **Next
abstract**

**Session 12 - Cosmology, Large-Scale Structure and Distance Scales.**

*Display session, Monday, June 10*

*Great Hall, *

## [12.09] The H/D/He Chemistry of the Early Universe

*P. C. Stancil (UNLV), A. Dalgarno (CfA), B. Zygelman, S. Lepp (UNLV)*
We present a comprehensive H/D/He chemistry of the
postrecombination epoch of the early universe. Fractional abundances of
e^-, H, H^+, H^-, D, D^+, D^-, He, He^+, H_2, H_2^+, HD,
HD^+, He_2^+, HeH^+, HeD^+, H_3^+, and H_2D^+ are calculated
for redshifts z between 4000 and 10. 90 reactions are included
with their rate coefficients
taken from the most recent theoretical or experimental evaluations.
Enhancements to the formation of HeH^+ and HeD^+ through
stimulated radiative association are also included. Rate coefficients for
this process will be presented.

We find the isotope abundance ratios
[D^-]/[H^-], [HD^+]/[H_2^+], [HD]/[H_2], and
[H_2D^+]/[H_3^+] to be enhanced
compared to the primordial abundance ratio
[D]/[H]=4\times 10^-5 by factors of up to
\sim 50. Conversely, the [D^+]/[H^+] and
[HeD^+]/[HeH^+] ratios are reduced by a factor of about 10^5
since for z<40, D^+ is significantly depleted due to
D^+ + H \to D + H^+. The reverse reaction
is endothermic by 43 K. HeD^+ is reduced since it is formed through
He + D^+ \to HeD^+ + \nu.

The calculations
are in fair agreement with Palla et al. (1995, ApJ, 451, 44)
for H, H^+, H^-, H_2, and HD.
Palla et al. appear to have overestimated the asymptotic
(i.e., for z\to 0) fractional abundances
of H_2^+, H_3^+, and H_2D^+ by factors ranging from 10^2
to 10^7 while HD^+ was underestimated by about a factor of 10^4.
The ratios [HD]/[H_2] and [H_2D^+]/[H_3^+] are in fair
agreement, but the HD^+ discrepancy persists for [HD^+]/[H_2^+].

Dubrovich (1993, Astron. Lett., 19, 53) has suggested that if the abundance
of H_2D^+ is large enough, it may be detected by Thomson scattering of
cosmic background
radiation (CBR) photons.
Palla et al. found the H_2D^+ fractional abundance to be to small
(\sim 10^-16) to have an effect on the CBR spectrum; we confirm
this result by calculating an even smaller H_2D^+ fractional abundance.

This work was supported by NSF grants OSR-9353227 and AST 93-01099.

**Program
listing for Monday**